Midterm Prep

Chapters 1-13

1 10 / 10 pts
State what the acronym MALDI-TOF MS stands for.

Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

2

Polymerase chain reaction (PCR) includes all the following steps, except:
denaturation. primer annealing. extension. gene expression.

gene expression.
Gene expression is the activation of DNA, which is not part of PCR. One PCR cycle consists of three steps: (1) denaturation of target DNA, (2) primer annealing to the target sequence, and (3) primer extension.

3

Antibiotic mechanisms of action target all the following, except:
Bacterial cell wall synthesis DNA replication
RNA transcription Bacterial plasmid DNA

Bacterial plasmid DNA

Although the classification scheme and number of antibiotics is complex and continues to expand as new classes emerge or existing classes are modified, their mechanisms of action target bacterial cell wall biosynthesis, folate synthesis, DNA replication, RNA transcription, and mRNA translation. These are logical targets critical to the survival of the microorganism.

4

Intrinsic mechanisms of resistance are:
those that inhibit protein synthesis and RNA transcription. those that a bacterium acquires through plasmids.
also called inducible enzymes.
innate characteristics of the bacterium and transmitted to progeny.

innate characteristics of the bacterium and transmitted to progeny.
Intrinsic mechanisms of resistance are carried in the bacterial genome and transmitted from generation to generation.

5

Acquired antibiotic resistance mechanisms include:
efflux mechanisms.
acquisition of new targets.
modification of existing antibiotic targets.

all of the listed answers

all of the listed answers
This section focuses on acquired mechanisms such as efflux, modification of existing antibiotic targets, acquisition of new targets, and production of enzymes that inactivate the antibiotic.

6

When should antimicrobial susceptibility testing be performed on a bacterial isolate from a clinical specimen?
A. When the isolate is determined to be a probable cause of the patient’s infection
B. When the susceptibility of the isolate to particular antimicrobial agents cannot be reliably predicted C. When the organism is part of the normal microbiota
both A and B

Both A and B
Antimicrobial susceptibility testing should be performed on a bacterial isolate from a clinical specimen if the isolate is determined to be a probable cause of the patient’s infection and the susceptibility of the isolate to particular antimicrobial agents cannot be reliably predicted. Susceptibility tests are not performed on bacteria that are predictably susceptible to the antimicrobial agents commonly used to treat infections caused by these bacteria.

7

Important factors that must be considered when determining whether antimicrobial susceptibility testing is warranted include:
the body site from which the organism was isolated.
the presence of other bacteria and the quality of the specimen from which the organism was grown. the host’s status.
all of the listed answers

all of the listed answers
In addition to the unpredictable susceptibility of a potential pathogen, other important factors must be considered when determining whether antimicrobial susceptibility testing is warranted; these factors include the following: the body site from which the organism was isolated, the presence of other bacteria, the quality of the specimen from which the organism was grown, and the host’s status.

8

Why would normal flora isolating from immunosuppressed patients undergo antimicrobial susceptibility testing?
These are not normal flora; they are other potential pathogens that have the same colonial morphology as normal flora.
Species usually viewed as normal flora may be responsible for an infection in an immunosuppressed patient.
All bacteria isolated from immunosuppressed patients must have antimicrobial susceptibility tests performed.
Cultures from immunosuppressed patients only grow pathogenic organisms that must undergo antimicrobial susceptibility testing.

Species usually viewed as normal flora may be responsible for an infection in an immunosuppressed patient.

The host status of the patient often influences susceptibility-testing decisions. Species usually viewed as normal flora may be responsible for an infection and at times may require testing in immunosuppressed patients.

9

What is the most critical step in any susceptibility test?
Plate streaking Organism isolation Gram stain identification Inoculum preparation

Organism isolation

10

What is the most widely used method of inoculum standardization?
McFarland turbidity standards Remel inoculum standards Becton-Dickson standards Difco standards

McFarland turbidity standards

The most widely used method of inoculum standardization involves McFarland turbidity standards.

11

The minimal inhibitory concentration (MIC) is:
the lowest antibiotic concentration to slow the growth of an organism. the highest antibiotic concentration to slow the growth of an organism. the lowest antibiotic concentration to inhibit the growth of an organism. the highest antibiotic concentration to inhibit the growth of an organism.

the lowest antibiotic concentration to inhibit the growth of an organism.

Dilution antimicrobial susceptibility test methods are used to determine the MIC, or the lowest concentration of antimicrobial agent required to inhibit the growth of a bacterial isolate.

12

In this type of antimicrobial susceptibility test, a McFarland 0.5 standardized suspension of bacteria is swabbed over the surface of a Mueller-Hinton agar plate, and paper disks containing single concentrations of each antimicrobial agent are placed onto the inoculated surface. What is the name of this test?
Kirby-Bauer MIC Breakpoint Agar dilution

Kirby-Bauer

The disk diffusion test, also commonly known as the Kirby-Bauer test, has been widely used in clinical laboratories since 1966, when the first standardized method was described. A McFarland 0.5 standardized suspension of bacteria is swabbed over the surface of a Mueller-Hinton agar plate, and paper disks containing single concentrations of each antimicrobial agent are placed onto the inoculated surface. After overnight incubation, the diameters of the zones produced by antimicrobial inhibition of bacterial growth are measured, and the isolate is interpreted as either susceptible, intermediate, or resistant to a particular drug, according to preset criteria.

13

Molecular Diagnostics includes all the following except:
Nucleic acid hybridization assays Enzyme-linked immunosorbent assays Amplification techniques
Strain typing techniques

Enzyme-linked immunosorbent assays

14

Nucleic Acid Hybridization assays may be used directly on specimens.
True
False

True

Classify the Antibiotic Resistance threats from the CDC’s watchlist: Urgent Threats

Carbapenem-resistant Enterobacteriaceae (CRE)

Clostridium difficile

Drug-resistant Neisseria gonorrhoeae

Multidrug-resistant Acinetobacter

Candida auris

Carbapenem-resistant Acinetobacter

Classify the Antibiotic Resistance threats from the CDC’s watchlist: Concerning Threat

Clindamycin-resistant group B Streptococcus

Erytrhomycin-resistant group A streptococcus

Classify the Antibiotic Resistance threats from the CDC’s watchlist: Serious Threat

Drug-resistant Campylobacter

Drug-resistant Non-typhoidal Salmonella

Drug-resistant Salmonella Typhi

Drug-resistnat Shigella

Drug-resistant Streptococcus pneumoniae

Drug-resistnat tuberculosis

Extended spectrum beta-lactamase producing Enterobacteriaceae (ESBLs)

Classify the Antibiotic Resistance threats from the CDC’s watchlist: Watch List

Azole-resistant Aspergillus fumigatus

Drug-resistant Mycoplasma genitalium

Drug-resistant Bordetella pertussis

16 2 / 2 pts
On the Blood Culture Instrument the sensor changes from [blank1] color to [blank2] color in the presence of CO2 produced by growing microorganisms which causes the bottle to alarm as positive.

gray

yellow

17 2 / 2 pts
AES (microbial identification) uses [blank1] technology and AST (susceptibility testing) uses [blank2] technology.

Colorimetric

turbidimetric

18 3 / 3 pts
Match the three ways we test for MRSA with what is being detected.
PCR

lateral flow

AST

mecA

PBP2a

Oxacillin

19 1 / 2 pts
Kirby Bauer antibiotic susceptibility testing includes [blank1] that have an MIC with an interpretation and [blank2] that only have an interpretation based on the zone size.

Etests

Disks

20
Selective media:
Support the growth of one type or group of microbes, but not another
Allow the growth of fastidious microbes through the addition of certain growth enhancers Support grouping of microbes based on different characteristics demonstrated in the media Support the growth of most non-fastidious microbes

Support the growth of one type or group of microbes, but not another

21
Differential media:
Support grouping of microbes based on different characteristics demonstrated in the media Allow growth of fastidious microbes through the addition of certain growth enhancers Support the growth of most nonfastidious microbes
Support the growth of one type or group of microbes, but not another
Wrong answer

Support grouping of microbes based on different characteristics demonstrated in the media

22

An enrichment broth is:
A broth that has growth enhancers to allow fastidious organisms to flourish
Used as a supplement to agar plates to detect small numbers of most aerobes, anaerobes, and microaerophiles
A liquid medium designed to encourage the growth of small numbers of a particular organisms while suppressing other flora A broth that allows the grouping of microbes based on different characteristics demonstrated in the medium

A liquid medium designed to encourage the growth of small numbers of a particular organisms while suppressing other flora

23

The steam autoclave method of sterilization:
Uses 15 lbs of pressure for 15 minutes at 121°C and quality control vial of Bacillus stearothermophilus
Utilizes 15 lbs of pressure , dry heat for 20 minutes, 121°C and quality control vial of Bacillus stearothermophilus

Produces a maximum temperature of 100o C under 15 lbs of pressure for 15 minutes and includes quality control vial of Bacillus stearothermophilus
Requires a source of ethylene oxide and quality control vial of Bacillus stearothermophilus while using 15 lbs of pressure
Wrong answer

Uses 15 lbs of pressure for 15 minutes at 121°C and quality control vial of Bacillus stearothermophilus

24

Because cell wall-damaged bacteria, antibiotic-treated bacteria, or dead bacteria may appear falsely gram-negative, what are “critical characteristics?”
Color and cell-wall composition Growth characteristics
Shape and size
Size and color

Shape and size

25

Which of the following combination of organisms may be used as quality control for the PYR test?
Staphylococcus epidermidis / Staphylococcus saprophyticus Staphylococcus aureus / Staphylococcus epidermidis Streptococcus pyogenes / Enterococcus faecalis Enterococcus faecalis / Streptococcus bovis

Enterococcus faecalis / Streptococcus bovis

26

What is the first step that can be performed to prevent many misidentifications?
gram stain morphology colony morphology biochemicals
google

gram stain morphology

27

In the laboratory, the clinical microbiologist is responsible for all the following, except
isolating microorganisms.
selecting treatment for patients. identifying microorganisms.
analyzing bacteria that cause disease.

selecting treatment for patients.

Clinical microbiologists do not select the treatment for patients. They provide the doctor with the name of the organism and the antibiotics that can kill the bacteria, but not in the final selection of treatment protocols.

28

What enables the microbiologist to select the media for primary culture and optimize the chance of isolating a pathogenic organism?
Determining staining characteristics
Understanding the cell structure and biochemical pathways of an organism Understanding the growth requirements of potential pathogens at specific body site Knowing the differences in cell walls of particular bacteria

Understanding the growth requirements of potential pathogens at specific body site Knowing the differences in cell walls of particular bacteria

By understanding growth requirements, a microbiologist can maximize the chance of the organism being isolated from a culture. The other three choices are used to identify a bacterium once it has grown on media.

29

This constituent of a gram-positive cell wall absorbs crystal violet but is not dissolved by alcohol, thus giving the gram-positive cell its characteristic purple color.
Mycolic acid Cholesterol Carbolfuchsin Peptidoglycan

Peptidoglycan
Mycolic acid is part of the cell wall of the Mycobacterium and Nocardia spp., but does not play a part in the Gram stain. Cholesterol is also part of the cell membrane, not the cell wall, so it does not play a part in the Gram stain. Carbolfuchsin is a stain used in bacteriology.

30

When performing a Gram stain on a gram-negative organism, the crystal violet is absorbed into this outer cell wall layer, and then washed away with the acetone alcohol. What is the main component of the outer layer of the cell wall?
Peptidoglycan
Mycolic acid N-acetyl-D-muramic acid Lipopolysaccharide

Lipopolysaccharide
Peptidoglycan is a thinner layer under the lipopolysaccharide in a gram-negative organism, whereas mycolic acid is the waxy layer present in a mycobacterium’s outer cell wall, and N-acetyl-D-muramic acid is part of the peptidoglycan.
Wrong answer

31

The three regions of the lipopolysaccharide include all the following, except
antigenic O-specific polysaccharide. mycolic acid.
core polysaccharide.
endotoxin (inner lipid A).

mycolic acid.

Antigenic O-specific polysaccharide, core polysaccharide, and endotoxin are all part of the lipopolysaccharide layer.

32

The outer cell wall of the gram-negative bacteria serves three important functions, which includes all the following, except:
It provides an attachment site for the flagella, which will act in locomotion. It acts as a barrier to hydrophobic compounds and harmful substances.
It acts as a sieve.
It provides attachment sites that enhance adhesion to host cells.

It provides an attachment site for the flagella, which will act in locomotion.

The outer cell wall of gram-negative bacteria acts as a barrier to hydrophobic compounds and harmful substances, acts as a sieve, and provides attachment sites that enhance adhesion to host cells. Flagella attach to the cell membrane, not to the cell wall.

33

What is the purpose of a capsule?

Prevent osmotic rupture of the cell membrane
Make up the periplasmic space
Act as a virulence factor in helping the pathogen evade phagocytosis Provide an attachment site for somatic antigens

Act as a virulence factor in helping the pathogen evade phagocytosis

The capsule acts as a virulence factor in helping the pathogen evade phagocytosis because antibodies have difficulty attaching to the capsule of bacteria and therefore are unable to prepare the organism for ingestion. The cell membrane is not prone to osmotic rupture when inside a host; the periplasmic space is found between the peptidoglycan and the lipopolysaccharide layers of the cell wall in gram-negative organisms; and somatic antigens are found below the capsule.

34

The Gram stain is a routine stain used in bacteriology to determine gram-positive and gram-negative bacteria based on the
phenotypic characteristics of the organism. composition of the bacterial cell wall. composition of the bacterial cell membrane. composition of the bacterial pili.

composition of the bacterial cell wall.

The composition of the bacterial cell wall is routinely used in bacteriology. The peptidoglycan cell walls of the gram-positive bacteria retain the crystal violet (purple) stain, whereas crystal violet stain is washed away because of the lipopolysaccharide (outer membrane) present in the cell walls of the gram-negative cells. The outer membrane retains the Safranin (pink) with the counter stain.

35

Which of the following environmental factors influence the growth of bacteria in the laboratory?
pH
Temperature
Gaseous composition of the atmosphere

All of the above

All of the above
Most bacteria grow best at a pH between 7.0 and 7.5, at 35° C, with a requirement for the gaseous composition of the atmosphere. Some bacteria require higher than atmospheric moisture (humidity) levels for optimal growth (Neisseria sp.).

36

Some bacteria grow at 25° C or 42° C, but diagnostic laboratories routinely grow pathogenic bacteria at what temperature?
30° C 60° C 35° C 10° C

35° C

Most pathogenic bacteria grow well at 35° C because it is close to body temperature; 30° C is the temperature at which most medically important fungi grow well; 60° C is too hot for pathogenic bacteria to grow, and 10° C is too cold for pathogenic bacteria to grow.

37

Which of these bacteria cannot grow in the presence of oxygen?
Obligate aerobes Capnophilic organisms Facultative anaerobes Obligate anaerobe

Obligate anaerobe

An obligate anaerobe is a bacterium that is killed when exposed to normal atmospheric conditions of oxygen and requires strict absence of oxygen. An obligate aerobe is a bacterium that grows only in the presence of oxygen, and a capnophilic bacterium grows only in the presence of 5% to 10% carbon dioxide.

38

Diagnostic schemes in the microbiology laboratory typically analyze each unknown bacterium’s metabolic processes for all the following, except
utilization of a variety of substrates as carbon sources. energy utilization for metabolic processes.
production of specific end products from specific substrates. production of an acid or alkaline pH in the test medium.

energy utilization for metabolic processes.

The microbiologist examines production of specific end products, production of an acid or alkaline pH in the test medium, and utilization of various carbon sources for energy to identify bacteria. Identification schemes are based on the percentages of bacterial species that exhibit particular metabolic processes in vitro.

39

In the medical microbiology laboratory, the ability of a gram-negative bacterium to ferment this sugar is the first step in its identification.
Sucrose Mannitol Trehalose Lactose

Lactose
Media used for gram-negative bacillus that contain this sugar allow for the differentiation into lactose fermenters and nonlactose fermenters. With this characteristic, organisms can be placed into these two large groupings. This aids in the identification of gram-negative organisms.

40

A _ is a single, closed, circular piece of DNA that is supercoiled to fit inside a bacterial cell.
phenotype chromosome frame-shift mutation transposon

chromosome

Chromosomes contain the genome of a bacterial cell. The DNA in the genome must be compacted and wrapped around protein molecules to fit inside the cell nucleus. This compacting, wrapping, and supercoiling makes up the chromosome.

41

Genes that code for antibiotic resistance are often found on small, circular pieces of DNA. These DNA pieces are called
plasmids. phenotypes. chromosomes. genomes.

plasmids

Plasmids found in bacteria are small, extrachromosomal DNA. Plasmids are found in the cytoplasm and can be replicated and passed on to daughter cells. Plasmids contain the antibiotic resistance genes for some antibiotics.

42

What process involves transferring or exchanging genes between similar regions on two separate DNA molecules? IS element
Replication Recombination Transcription

Recombination

Recombination is the process described. Transcription occurs when a DNA molecule makes an RNA molecule. Replication occurs when DNA is used to make another DNA molecule. An IS element is a type of mutation that occurs when a small piece of DNA jumps from one area in a chromosome to another.

43

A microbiologist is working with two separate cultures of the same organism. The bacteria in one culture are resistant to penicillin, whereas the bacteria in the other culture are susceptible to penicillin. The bacteria from both cultures are mixed together, and all the resulting bacteria are resistant to penicillin. What caused this phenomenon?
The plasmid carrying the resistance gene was transferred to the susceptible population of bacteria.
The plasmid carrying the susceptibility gene was transferred to the resistant population of bacteria.
An IS element was inserted into the genome of the susceptible bacterial population.
A frame-shift mutation occurred that allowed the susceptible population of bacteria to develop resistance to penicillin.

The plasmid carrying the resistance gene was transferred to the susceptible population of bacteria.
Antibiotic resistance is carried by plasmids, which can easily be transferred from one bacterium to another. The receiving bacterium then displays the characteristics contained in the plasmid. IS elements and frame-shift mutations occur on the chromosomes and take longer to manifest than do plasmid transfers.

44

Organisms that participate in a biological relationship where both benefit from one another are called
parasites. symbionts. hosts. flora.

symbionts

Symbiosis is a relationship where two organisms live together and their association benefits both organisms. Organisms that live in symbiosis are said to be symbionts. Parasites are organisms that live off a host and harm the host. The host is the organism that provides the nutrients to the other organisms. Flora are described as microorganisms that inhabit the body sites of healthy individuals.

45 Parasitism is
a biological relationship between two or more organisms in which both benefit from one another.
a biological relationship between only two organisms in which there are no beneficial or harmful effects to the host. a biological relationship in which one species gains benefits at the expense of the host.
a synonym for mutualism.

a biological relationship in which one species gains benefits at the expense of the host.
When both organisms live together and one organism benefits at the expense of the host, this is parasitism. When both organisms live together and both benefit, this is symbiosis. When both organisms live together and neither benefits, this is commensalism. Mutualism and symbiosis are synonyms.

46

This bacterial state occurs when a host harbors a disease-causing organism, but does not show signs of disease.
Carrier
Transient Resident Indigenous

Carrier

Transient, resident, and indigenous refer to particular types of flora associated with the human body, whereas carrier refers to the state in which pathogenic organisms establish themselves in a host without causing disease, but the host can still transmit the infection.

47

Healthy people are colonized by many different bacteria in many different sites. These bacteria are referred to as
transient flora. carrier flora. maintenance flora. indigenous flora.

indigenous flora.

Indigenous flora are usual or normal flora, whereas transient flora are microbial flora that are present at a site temporarily. Carrier and maintenance flora are not types of microbial flora found on the human body.

48

Diabetics may sometimes be infected with their own resident flora. This type of infection is called
an opportunistic infection. a carrier state.
symbiosis.
a parasitic infection.

an opportunistic infection.

Opportunistic infections occur when the host has changes in body chemistry associated with age, disease states, and drug or antibiotic effects. Carrier states are those in which a host does not show symptoms of a disease, but it can infect other hosts with pathogenic organisms. Symbiosis is a biological relationship that benefits the host and the organism. A parasitic infection is one in which the parasite receives benefits, but at the expense of the host.
Wrong answer

49

A laboratory professional is testing a new antimicrobial soap. The tech washes her forearm then does a culture of the skin. Even though the tech washed with the antimicrobial soap, which organisms should/could she most likely expect to find growing in the culture?
Diphtheroids and Bacillus spp.
Staphylococcus epidermidis and Propionibacterium S. aureus and Propionibacterium
Diphtheroids and Propionibacterium
None of these organisms should be found.

Staphylococcus epidermidis and Propionibacterium

Superficial antisepsis of the skin does not kill the Propionibacterium and S. epidermidis that live in the hair follicles and sebaceous glands. Diphtheroids are found in moist areas such as the axillae and toes. S. aureus is typically a pathogen but can be found on healthy skin. Handwashing does not remove all bacteria from the skin.

50

What mechanism allows strict anaerobes to grow in the cervices and areas between the teeth when plaque is present?
A low oxidation-reduction potential occurs at the tooth surface under the plaque.
The bacteria secrete sugar to nourish the strict anaerobes.
The normal flora secrete antibiotics to kill all the other bacteria and allow the strict anaerobes to thrive. The plaque-causing bacteria secrete an alkaline fluid and change the pH around the tooth.

A low oxidation-reduction potential occurs at the tooth surface under the plaque.

The growth of the plaque-causing bacteria on the tooth’s surface contain as many as 1011 streptococci per gram, and this amount of bacteria lowers the oxidation-reduction potential at the tooth surface. Strict anaerobes cannot grow in the presence of oxygen, and lowering the oxidation-reduction potential lowers the amount of oxygen at the tooth surface. Normal oral flora organisms do not secrete sugar, antibiotics, or alkaline fluid.

51

The human body is constantly challenged by pathogens in the environment. It is not infected by every pathogen it encounters because the microbial flora
engulf the pathogenic bacteria.
produce conditions at the microenvironmental level that block colonization.
prime our immune system.
activate and support the action of antigen-presenting cells, cytokines, and cell-mediated immunity.

produce conditions at the microenvironmental level that block colonization.
Several mechanisms are used by microbial flora to ensure that colonization of pathogenic organisms is blocked, such as lowering the reduction- oxidation potential, lowering the pH, producing antimicrobials, and depleting the nutrients present in a particular environment.

52

The ability of an organism to produce disease in an individual is called
pathogenicity. iatrogenic infection. parasitic infection. opportunistic infection.

pathogenicity

An iatrogenic infection occurs as the result of medical treatment or procedure. A parasitic infection occurs when an organism invades a host and only the organism benefits from the biological relationship. An opportunistic infection occurs when the condition of the host changes and the resident cause an infection.

53

The smaller the number of microorganisms necessary to cause infection in a competent host, the more _ the microorganism.
opportunistic parasitic invasive virulent

virulent

Virulence refers to the relative ability of a microorganism to cause disease; more virulent organisms need fewer organisms to cause disease in a host. Opportunistic refers to a type of resident flora that causes infection when the conditions in a host change. A parasitic infection occurs when an organism invades a host and only the organism benefits from the biological relationship. Invasive refers to entering tissue, not the degree of ease with which an organism can cause disease.
Wrong answer

54

Factors that determine the pathogenicity and increase the virulence of organisms include all the following, except
an organism’s ability to avoid phagocytosis.
an organism’s ability to produce exotoxins and extracellular enzymes. an organism’s ability to produce infection when host conditions change. an organism’s ability to survive intracellularly when phagocytized.

an organism’s ability to produce infection when host conditions change.

An organism’s ability to produce infection when the host conditions change is referred to as an opportunistic pathogen. The other three statements refer to ways that a microorganism can survive the attack of a host’s immune system and produce disease.
flora

55

The most common bacterial characteristic that allows for evasion of phagocytosis by the host is called
exotoxin production. extracellular enzyme production. pili.
polysaccharide capsule.

polysaccharide capsule.
Organisms possessing a polysaccharide capsule are considered highly virulent because they can evade phagocytosis. Exotoxin and extracellular enzyme production and pili are factors that can increase an organism’s virulence. The exotoxins and extracellular enzymes may be used to survive phagocytosis, but these do not help an organism evade phagocytosis. Pili are used to transfer plasmids that may contain the genes for antimicrobial resistance and, therefore, help an organism survive in the host.

56

Changes in these host structures can result in lower virulence of a microorganism.
Pili
Adhesin receptors Surface polysaccharides Phagocytes

Adhesin receptors

Adhesin receptors are structures found on the host cell that are necessary for attachment of bacterial adhesins and the beginnings of an infection. Pili and surface polysaccharides are the main bacterial structures of attachments called adhesins. Phagocytes are white blood cells (WBCs) that engulf invading microorganisms.
Wrong answer

57

After attachment to host cells, a pathogen may use the following mechanisms to establish itself and cause disease, except:
Uses lactoferrin for iron
Produces an IgA protease that degrades the IgA at mucosal surfaces Produces lysozyme to kill the host cell
Circumvents host antibodies by shifting key cell-surface antigens

Produces an IgA protease that degrades the IgA at mucosal surfaces

After engulfing bacteria, the host cell releases lysosomal contents that kill the organism. The bacteria do not produce lysozyme.

58

Dissemination of a pathogen is
when a pathogen penetrates and grows in tissues.
when a pathogen multiplies intracellularly.
when a pathogen circumvents host antibodies by shifting key cell-surface antigens.
when infection with a pathogen spreads from the initial infection site to distant sites such as organs and tissues.

when infection with a pathogen spreads from the initial infection site to distant sites such as organs and tissues.

Invasion of a pathogen allows the microbe to take advantage of the host’s transport system (the blood) and seek out other areas that can be infected. This occurs only if the pathogen can elude the host’s immune system during this journey. Invasion is when a pathogen penetrates and grows in tissues. Intracellular multiplication of a pathogen occurs when an organism can survive phagocytosis. When a pathogen shifts key cell-surface antigens, it is evading a host’s immune system.
Wrong answer

59

A physician notices that several patients are infected with Clostridium difficile, but only a few of the patients are symptomatic for disease. The reason for this discrepancy is
only those strains of the organism carrying the extrachromosomal DNA coding for the toxin gene will produce toxin and cause the individuals to be symptomatic. only those strains of the organism carrying DNA coding for the toxin within its main DNA molecule will produce toxin and cause the individuals to be symptomatic. the exotoxin produced contains only the nontoxic portion.
the exotoxin must be produced in conjunction with extracellular enzymes to cause problems.

only those strains of the organism carrying the extrachromosomal DNA coding for the toxin gene will produce toxin and cause the individuals to be symptomatic.

The exotoxin gene is commonly encoded for by phages, plasmids, or transposons and does not normally reside within an organism’s main DNA molecule. Exotoxins are highly characterized molecules that are composed of a nontoxic subunit that binds the toxin to the host cells, allowing attachment of the toxin. Exotoxins exhibit their effects without the aid of extracellular enzymes. Extracellular enzymes are another factor that contributes to the virulence and invasiveness of organisms.
Wrong answer

60

The effects of endotoxins consist of dramatic changes in all the following, except
blood pressure. fluid imbalance. clotting.
body temperature.

blood pressure.

Unlike shock caused by fluid loss, such as that seen in severe bleeding, septic shock is unaffected by fluid administration. An increase in body temperature occurs within an hour after exposure. Severe hypotension occurs within 30 minutes after exposure. The endotoxin also initiates coagulation, which can result in intravascular coagulation.
Wrong answer

61

Healthy skin secretes these substances to help prevent colonization by transient and possibly pathogenic organisms.
Long-chain fatty acids Sebaceous glands Carbohydrates Antibodies

Long-chain fatty acids

Long-chain fatty acids produced by the sebaceous glands allow the skin environment to be acidic, leading to a low pH environment. Many pathogens prefer the near-neutral environment in the body to produce disease. Bacteriocidal substances are produced by the microbial flora that colonize the skin, and antibodies are produced by lymphocytes.

62

Pathogens can be transmitted through all the following routes, except
ingestion. handwashing. sexual contact. air.

Handwashing is a major method to prevent spread of infections. Pathogens can be transmitted by ingestion, sexual contact, and air.

63
2.5 / 2.5 pts
Thioglycolate Broth growth

top only

bottom only

throughout

gas exchange

pink in oxygen and colorless without oxygen

strict aerobes

anaerobes

facultative organisms

aerobes

resazurin

64

More ____ one species with greater than 105 colony-forming units (CFUs)/mL suggest contamination (especially in urine cultures).

two

65

All cells in a population have the mecA gene, but not all of them are actively expressing the gene at a given time.
Heteroresistance
Low Affinity Intermediate Resistance Inactive

Heteroresistance

67
2 / 2 pts
Steps of Gram Stain

crystal violet

iodine

ethanol (or acetone’alcohol)

safranin

primary stain

mordant

decolorizer

counterstain

68
1 / 2 pts
Resistance Markers

VREs

CREs

ESBLs

ORSAs

VanA, VanB, VanC

VIM, NDM-1, IMP, KPC, OXA

CTX-M, MBLs, AmpC

MecA, PBP2a

69

After using the phone, the laboratory tech sprayed the receiver with a chemical spray. This process will kill a defined scope of microorganisms. What is this process called?
Sterilization Bacteriostatic Disinfection Bactericidal

Disinfection kills a defined scope of microorganisms. Sterilization kills all organisms and spores at a site. Bacteriostatic and bactericidal are adjectives that describe the particular action of chemical agents: to inhibit bacterial growth or kill bacteria.

70

Biochemical tests are based on the _ of microorganisms.
phenotype genotype plasmid lysogeny

The colony morphology, Gram stain, and biochemical testing are based on the phenotype of the bacterium. The phenotype is the expressed characteristics in the bacteria. The genotype is the actual nucleic acid sequences present in the bacterium’s DNA. Plasmids can be responsible for antimicrobial resistance, but they do not alter colony morphology or biochemical tests. Lysogeny is infection of the bacteria with a virus.

71

Nucleic acid assays are based on the _ of the organism and are believed to be more accurate.
phenotype genotype plasmid lysogeny

The genotype is the actual nucleic acid sequences present in the bacterium’s DNA. The colony morphology, Gram stain, and biochemical testing are based on the phenotype of the bacterium. The phenotype is the expressed characteristics in the bacterium. Plasmids can be responsible for antimicrobial resistance, but they do not alter colony morphology or biochemical tests. Lysogeny is infection of the bacteria with a virus.
Wrong answer

72

Which of the following descriptions will directly facilitate identification of bacteria?
Environmental growth temperature
Physical characteristics of colony morphology Environmental growth atmosphere
Colony color

physical characteristics of colony morphology

Many specific microorganisms have characteristics that distinguish them in a crowd of genera or species. This characterization of colonies on culture media facilitates presumptive identification of commonly isolated organisms.

74

Data generated by the laboratory is directly influenced by
the quality of the specimen and its condition when received. the physician’s decision to do the test.
quality control performed on a monthly basis.
the air quality in the laboratory.

the quality of the specimen and its condition when received.

The old adage of garbage in–garbage out applies here. High-quality specimens result in high-quality laboratory results. Even though the laboratory professional does not usually perform the preanalytic process of collecting microbiology specimens, it directly affects the outcome.

75

If a test is not considered appropriate for the specimen, the following should happen:
Discipline the ward clerk for ordering the wrong test.
Discipline the nurse for ordering the wrong test.
Hold a training session to teach hospital staff about ly ordering tests.
The laboratory needs to communicate with the physician to determine exactly what needs to be done.

The laboratory needs to communicate with the physician to find out what needs to be done. Disciplining the ward clerk and the nurse is not a solution to this problem. They do not know what are and what are not appropriate tests for each specimen. Because each situation is different, there is no need for a staff training session.
Wrong answer

76

Nonselective media supports
the grouping of microbes based on different characteristics demonstrated in the media. the growth of one type or group of microbes, but not another.
the growth of most nonfastidious microbes.
the growth of fastidious microbes through the addition of certain growth enhancers.

Nonselective media support the growth of most nonfastidious microbes. Selective media support the growth of one type or group of microbes, but not another. Differential media allow grouping of microbes based on different characteristics demonstrated on that medium. Enriched media contain growth enhancers that are added to nonselective agar to allow fastidious organisms to flourish.

77

What method is used to concentrate specimens to increase recovery of pathogens in the microbiology laboratory?
Homogenization Centrifugation Mixing Anticoagulation

Using a centrifuge can help the microbiology technologist concentrate pathogenic organisms at the bottom of the tube in liquid specimens. This is usually performed when the specimen volume is large. Homogenization is used to release pathogens that may be trapped in a tissue. Mixing a specimen will spread out the pathogenic organisms as opposed to concentrating them.
Wrong answer

78

If a 0.001 mL quantitative loop is used to inoculate plate media for a urine culture, each colony of growth represents how many organisms per milliliter in the original sample?
1 organism
10 organisms 100 organisms 1000 organisms

0.001 mL of urine streaked onto a plate will give colony counts in multiples of 103. Therefore, each colony of growth represents 1000 organisms or colony-forming units per milliliter in the original sample.

Chapter 14, 15, 17

1 3 / 3 pts
How long is an urine specimen acceptable for culture?

Unpreserved and Unrefrigerated?
Unpreserved and Refrigerated?
Preserved and Refrigerated or Unrefrigerated?

2 hrs

48 hrs

72 hrs

2

All of the following staphylococci are coagulase-positive, except
S. delphini.
Staphylococcus aureus.
S. intermedius.

S. saprophyticus.

S. saprophyticus.
The staphylocoagulase-producing (coagulase-positive) staphylococci are S. aureus, S. intermedius, S. delphini, S. lutrae, and some strains of S. hyicus.

3

Staphylococcal enterotoxin B is linked to
pneumonia.
staphylococcal pseudomembranous enterocolitis. carbuncles.
middle ear infections.

staphylococcal pseudomembranous enterocolitis.

Enterotoxin B has been linked to staphylococcal pseudomembranous enterocolitis, although the mechanism is not understood. It can be a form of food poisoning. Enterotoxin B has also been linked to some cases of toxic shock syndrome (TSS).

4

What is the mechanism by which toxic shock syndrome toxin-1 (TSST-1) causes TSS?
The bacteria release the toxin into the gastrointestinal system where phagocytes engulf the bacteria, leaving a pseudomembrane that irritates the colon.
The toxin is a superantigen that stimulates T-cell proliferation with production of large amounts of cytokines.
The bacteria release the toxin into the blood and it goes to the hypothalamus to produce an extremely high fever. All of the above

TSST-1 is a superantigen stimulating T-cell proliferation and the subsequent production of a large concentration of cytokines that are responsible for the symptoms. At low concentration, TSST-1 causes leakage by endothelial cells, and at higher concentration, it is cytotoxic to these cells. TSST-1 is absorbed through vaginal mucosa, permitting the systemic effects seen in TSS.

5

What are the effects of the α-hemolysin produced by Staphylococcus aureus?
It acts on sphingomyelin in the plasma membrane of red blood cells.
It kills macrophages.
It kills polymorphonuclear leukocytes.
It lyses red blood cells, damages platelets and macrophages, and can cause severe tissue damage.

β-Hemolysin (sphingomyelinase C) acts on sphingomyelin in the plasma membrane of the erythrocytes and is also called the “hot-cold” lysin. This hemolysin is exhibited in the CAMP test performed in the laboratory to identify Group B streptococci.

6

What are the effects of the Panton-Valentine toxin produced by Staphylococcus aureus?
It acts on sphingomyelin in the plasma membrane of red blood cells.
It lyses red blood cells, damages platelets and macrophages, and can cause severe tissue damage.
It kills epithelial cells.
It kills leukocytes.

Staphylococcal leukocidin, Panton-Valentine leukocidin (PVL), is an exotoxin lethal to polymorphonuclear leukocytes, macrophages, and monocytes. It has been implicated as contributing to the invasiveness of the organism by suppressing phagocytosis and has been associated with severe cutaneous infections and necrotizing pneumonia. Although produced by relatively few strains of Staphylococcus aureus, it has been associated with some cases of community-acquired staphylococcal infections.

7

All of the following enzymes are produced by staphylococci, except
protease.
hyaluronidase.
amylase. lipase.

amylase

Several enzymes are produced by staphylococci. Examples are coagulase, protease, hyaluronidase, and lipase.

8

What is the function of protein A in the cell wall of Staphylococcus aureus?
To block the activation of the complement cascade
To bind IgG and prevent phagocytosis
To bind IgM and inactivate natural killer cells
To keep the structural integrity of the cell wall and keep out antimicrobial agents

To bind IgG and prevent phagocytosis

Protein A is one of several cellular components that have been identified in the cell wall of S. aureus. Probably the most significant role of protein A in infections caused by S. aureus is its ability to bind the Fc portion of IgG. Binding IgG in this manner can block phagocytosis.

9

The primary reservoir for staphylococci is
nares.

throat. mouth. ears.

The primary reservoir for staphylococci is the nares, with colonization also occurring in the axillae, vagina, pharynx, and other skin surfaces. Nasal carriage in patients admitted to the hospital is common. Because close contact among patients and hospital personnel is not unusual, transfer of organisms often takes place.

10

The development of staphylococcal infection is determined by
size of the inoculum.
status of host’s immune system.
virulence of the strain.
All of the above

As with most infections, the development of staphylococcal infection is determined by the virulence of the strain, size of the inoculum, and status of the host’s immune system. Infections are initiated when a breach of the skin or mucosal barrier allows staphylococci access to adjoining tissues or the bloodstream.

11

Infections caused by Staphylococcus aureus are suppurative, meaning
these infections ooze lymph fluid.
the toxins activate the coagulation system, which isolates the infection.

the infection is filled with pus and necrotic tissues.
the acute inflammatory response gorges the area with red blood cells.

Infections caused by S. aureus are suppurative. Typically the abscess is filled with pus and surrounded by necrotic tissues and damaged leukocytes.

12

This disease is an extensive exfoliative dermatitis caused by staphylococcal exfoliative toxin.
TSS
Ritter’s disease Bullous impetigo Folliculitis

Scalded skin syndrome, or Ritter’s disease, is an extensive exfoliative dermatitis that occurs primarily in newborns and previously healthy young children. This syndrome is caused by staphylococcal exfoliative or epidermolytic toxin produced by Staphylococcus aureus phage group II, probably present at a lesion distant from the site of exfoliation.

13

This is a rare but potentially fatal multisystem disease characterized by high fever, hypotension, and shock, and it is associated with highly absorbent tampons.

TSS
Scalded skin syndrome Toxic epidermal necrolysis Bullous impetigo

TSS is a rare but potentially fatal multisystem disease characterized by high fever, hypotension, and shock. It was first described by Todd in 1978 and was associated with highly absorbent tampon use. Some cases appear in men, children, and nonmenstruating women.

14

Staphylococcus aureus food poisoning is most commonly caused by these two enterotoxins.
A and B
B and C
A and D B and D

S. aureus enterotoxins, most commonly A and D, have been identified and associated with gastrointestinal disturbances. The source of contamination is usually an infected food handler. Staphylococcal food poisoning is a type of intoxication, resulting from the ingestion of a preformed toxin.

15

This infection occurs secondary to influenza A virus, has a high mortality rate, and occurs among the infants and immunocompromised patients.
Staphylococcal pneumonia Gangrene
Staphylococcal meningitis Staphylococcal peritonitis

Staphylococcal pneumonia has been known to occur secondary to an influenza A virus infection. Although rare, staphylococcal pneumonia has a high mortality rate. The pneumonia, which develops as either a contiguous lower respiratory tract infection or a complication of bacteremia, is characterized by multiple abscesses and focal lesions in the pulmonary parenchyma. Infants and immunocompromised patients, such as the elderly and patients receiving chemotherapy or immunosuppressants, are most affected.

16

Infections by this organism are predominantly hospital acquired, and some predisposing factors include catheterization, medical implantation, and immunosuppressive therapy.

S. epidermidis
S. saprophyticus Staphylococcus aureus S. intermedius

The role of S. epidermidis as an etiologic agent of disease has become increasingly evident. Infections caused by S. epidermidis are predominantly hospital acquired. Some of the predisposing factors are instrumentation procedures, such as catheterization, medical implantation, and immunosuppressive therapy. S. epidermidis is probably the most common cause of hospital-acquired urinary tract infections.

17

This staphylococcal species is associated with urinary tract infections in young, sexually active females.
S. intermedius

S. saprophyticus Staphylococcus aureus S. epidermidis

S. saprophyticus has been associated with urinary tract infections in young, sexually active females. This species is found to adhere more effectively to the epithelial cells lining the urogenital tract than other coagulase-negative staphylococci.

18

All of the following is used to describe the colony morphology of Staphylococcus epidermidis, except
β-hemolytic.
small to medium.
nonhemolytic. white.

S. epidermidis colonies are usually small- to medium-size, nonhemolytic, white colonies.

19

The presence of mecA indicates
resistance to methicillin. Staphylococcus epidermidis. vancomycin resistance. sensitivity to tetracycline.

The mecA gene codes for an altered penicillin-binding protein found in the cell wall of staphylococci. The altered protein does not bind penicillin, rendering the cell penicillin resistant.

20

How is Staphylococcus saprophyticus presumptively identified?
Latex agglutination test for clumping factor

Novobiocin susceptibility
Rabbit plasma test for coagulase All of the above

Presumptive identification of S. saprophyticus is accomplished by testing for novobiocin susceptibility using a 5 μg novobiocin disk. S. saprophyticus is resistant to novobiocin, but most other coagulase-negative staphylococci are susceptible.