Intro to Microbiology - Quiz 4 - Chapters 12 & 13

A patient is admitted to the hospital with a diagnosis of endocarditis. Two separate blood cultures grow out of viridans streptococci. The penicillin MIC of the organism is 0.12 µg/mL. What antibiotic should the physician prescribe?

a.

Penicillin

Why are aminoglycosides not an effective treatment for meningitis?

a.

They do not cross the blood-brain barrier.

Oxacillin-resistant Staphylococcus aureus is called

a.methicillin-resistant S. aureus (MRSA).

What is the principle of the Etest?

b.Establishing an antimicrobial density gradient in agar

What is the principle of the most commonly used test to detect β-lactamase production?

a.

Chromogenic cephalosporin nitrocefin

What is generated by analysis of individual susceptibility results on isolates from a particular institution in a defined period and represents the percentage of isolates of a given species that is susceptible to the antimicrobial agents commonly tested against the species?

d.

Cumulative antibiogram

On a breakpoint panel, when two concentrations are tested and no growth is present in either well, the isolate is

a.

susceptible.

These two classes of antibiotics allow initiation and mRNA translation to begin, but they act by inhibiting peptide elongation.

c.

Macrolides and tetracyclines

Important factors that must be considered when determining whether antimicrobial susceptibility testing is warranted include

d.

All the above

Relatively nontoxic antimicrobial therapeutic agents include all of the following, except

a.

heavy metals.

What concentrations of antibiotics are typically tested in MICs?

.

d. Serial twofold dilution concentrations are tested.

All of the following antibiotics target the 50S ribosomal subunit to prevent mRNA translation in the bacteria, except

b.

quinolones.

This antibiotic affects the DNA replication by targeting topoisomerases II and IV, enzymes considered important in controlling DNA replication.

d.

Quinolone

Integrons are

c.

genetic elements capable of integrating resistance genes (cassettes) by an integron-encoded, site-specific recombinase.

Transposons are

b.

DNA elements that encode transposition and excision function and can transpose from one place on the chromosome to another.

The CLSI has published methods for susceptibility testing of several agents of potential bioterrorism, including Brucella anthracis, Yersinia pestis, Burkholderia mallei, B. pseudomallei, Francisella tularensis, and Brucella spp. How does CLSI suggest clinical laboratories perform antimicrobial susceptibility testing on these isolates?

d.

Do not attempt to perform antimicrobial susceptibility on any of these isolates; refer them to a public health laboratory equipped to handle them.

If the MIC or zone size is interpreted as resistant using the latest CLSI tables

c.

the patient's infecting organism is likely to require the maximum amount of antimicrobial or more than can be achieved and for which the clinical response is likely to be less than with a susceptible strain.

A 12-year-old girl goes to the doctor complaining of a sore throat, fever, headache, and general malaise. The doctor does a quick strep test that is positive for group A β-hemolytic Streptococcus. No antibiotic testing is needed because Streptococcus is

a.universally susceptible to penicillin.

Extended β-lactamases target all the following antibiotics, except

d.

macrolides.

This type of resistance mechanism modifies the antibiotic targets and results in reduced affinity of antibiotics for their microbial targets.

c.

Enzyme alteration

Efflux pumps

d.

function as transporter proteins involved in the removal of toxic substances from the interior of the cell to the external environment.

The minimum bactericidal concentration (MBC) test differs from the MIC test because the MIC test gives the concentration needed at the site of infection to inhibit bacterial multiplications, whereas the MBC gives

c.

the amount of antimicrobial that must be achieved at the infection site to kill the organism.

What is the mechanism of action of the glycopeptides (vancomycin and teicoplanin)?

c.

The glycopeptides bind to the substrate of the transpeptidation enzyme and disrupt the cell membrane construction.

The outer membrane of gram-negative bacteria is composed of

a.

lipopolysaccharides, phospholipids, and porin proteins.

Acquired mechanisms of resistance are those that

c.

result from acquisition of DNA by acquisition of extrachromosomal DNA.

Mechanisms that mediate intrinsic antibiotic resistance include all the following, except

d.

alternate biosynthetic pathways.

How are antibiotics chosen for inclusion into laboratory antimicrobial testing protocols?

d.

Both B and C.

After the plate is incubated in the Kirby-Bauer test, what occurs?

b.

The diameter of each inhibition zone for each antibiotic is measured using a ruler or caliper.

What principle does the VITEK series use to determine antimicrobial susceptibility?

a.

Turbidimetry

The BD Phoenix system uses this principle to measure bacterial growth in the susceptibility test wells.

d.Redox indicator system

A young, healthy patient goes into the hospital for reconstructive knee surgery and spikes a fever the day after surgery. The doctor finds the patient has a nosocomial infection with methicillin-resistant Staphylococcus aureus (MRSA). What antibiotic should the doctor use to treat this patient?

d.

Vancomycin

The minimal inhibitory concentration (MIC) is

c.

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

Agar dilution and disk diffusion tests for Streptococcus pneumoniae and Streptococcus spp. use

d.

Mueller-Hinton agar supplemented with 5% sheep blood.

Goals of combination antimicrobial therapy include all the following, except

d.ensure that at least one antimicrobial will obtain the MBC at the infection site.

When performing disk diffusion testing with Haemophilus influenzae and H. parainfluenzae, what type of medium is used?

b.Mueller-Hinton with hematin and nicotinamide adenine dinucleotide (NAD)

This antibiotic interferes with DNA transcription by blocking of RNA chain elongation.

a.

Rifampin

A microbiology technologist is performing a β-lactamase test on a staphylococcus isolated from a hospitalized patient. The test was negative, so the technologist reported out in vitro antimicrobial susceptibility test results for β-lactam antibiotics. After 2 days, the patient was not improving and the physician changed the patient's antibiotic to an aminoglycoside. The patient showed improvement immediately. Why was the β-lactamase test on the staphylococci negative, when the organism produced β-lactamase?

b.

Staphylococci must be exposed to the β-lactam agent before it will produce a positive test result.

What is a porin?

d.

Outer membrane channels that permit the inflow of nutrients and the outflow of wastes

Streptococcus pneumoniae and Streptococcus pyogenes use efflux as an effective mechanism for acquired resistance to

a.

macrolides.

The members of the polyketide class of antibiotics include all the following, except

d.

oxycycline.

In gram-positive bacteria, this is substantially thicker and more multilayered than in gram-negative bacteria.

c.

Peptidoglycan

In this method of antimicrobial susceptibility testing, specific volumes of various concentrations of antimicrobial solutions are dispensed into premeasured volumes of molten and cooled agar, which is subsequently poured into standard Petri dishes. Organisms are inoculated onto the plate. What type of antimicrobial susceptibility testing is this?

d.

Agar dilution

What agencies develop the zone interpretive criteria?

c.

FDA and CLSI

All of the following are β-lactam antibiotics, except

d.

monoterpenes.

This is one of the first resistance mechanisms identified and is a strategy that bacteria use successfully to survive the action of many classes of antibiotics.

c.Acquisition of inactivating enzymes

What is a mechanism for ensuring the testing personnel are proficient in their tasks?

d.

All of the above

Which antibiotic inhibits folate synthesis, providing the essential precursor molecule, pyridine thymidylate, needed in DNA synthesis?

d.

Sulfamethoxazole

How do the β-lactamase inhibitors work?

c.

By acting as substrates for the β-lactamase and reducing their effect on the antibiotic

Intrinsic mechanisms of resistance are

d.

innate characteristics of the bacterium and transmitted to progeny.

Both gram-positive and gram-negative bacteria have an inner cytoplasmic membrane that is composed of

b.phospholipids and proteins.

Guidance for the development of a selective-reporting or cascade-reporting protocol for antibiotics is available from the

b.

Clinical Laboratory and Standards Institute (CLSI).

Biofilms are groups of bacteria that are irreversibly attached to surfaces and are embedded in a matrix of extracellular polymeric substances. They are most commonly found on

c.

indwelling medical devices.

What is the most widely used method of inoculum standardization?

a.

McFarland turbidity standards

Quality control of antimicrobial susceptibility tests involves

c.

testing standard reference strains that have defined antimicrobial susceptibility (or resistance) to the drugs tested.

All of the following are recently approved classes of antibiotics that target protein synthesis, except

a.sixth generation cephalosporins.

Therapy of disseminated meningococcal infections and various types of gonococcal (GC) infections are

c.generally empiric based on recommendations of CDC.

Insertion sequences are

d.

DNA elements found in bacteria that carry genes only for the enzymes needed to promote their own transposition.

What antibiotics should be reported for urinary tract infections?

c.Urinary tract active agents

How does Staphylococcus aureus acquire resistance to methicillin?

b.Mobile DNA element

Antibiotic mechanisms of action target all the following, except

a.blocking the Embden-Meyerhof pathway.

This type of pathogen may demonstrate decreases or loss of porin synthesis in combination with other resistance mechanisms, resulting in multidrug-resistant pathogens.

a.

Nosocomial

Who sets the criteria in the table of values that relates the diameter of the zone to a category of susceptibility in disk diffusion testing?

c.

CLSI

On a breakpoint panel, when there is growth in the low concentration but no growth in the high concentration, the isolate is

c.intermediate.

What McFarland standard provides turbidity comparable to that of a bacterial suspension containing approximately 1.5 × 108 colony-forming units (CFU)/mL?

c.0.5

Which enterococcus is/are the most common species demonstrating vancomycin resistance among clinical isolates?

a.

Enterococcus faecium

What type of antimicrobial susceptibility testing method does CLSI recommend for anaerobes?

b.

Agar dilution

Resistance to aminoglycosides is mediated by

d.

All of the above

Spontaneous mutations occur in the β-lactamase genes that result in extended-spectrum β-lactamases (ESBL). These ESBL inactivate

d.All of the above

What is the storage temperature for frozen panels?

b.-20° C to -70° C

Antibiotics work by targeting all of the following, except

b.

bacterial plasmid DNA.

To obtain a bactericidal effect in enterococci, ampicillin or penicillin must be given in combination with

d.

aminoglycosides.

The primary mechanism of resistance to this antimicrobial class is modification by mutations encoding single amino acid changes in these targets. What antibiotic class is this?

b.

Quinolones

A patient undergoes a colon resection. Because of the amount of bacteria present in the colon, the physician put the patient on broad-spectrum antibiotics after surgery. The patient develops a fever 2 days after surgery. He developed an infection with vancomycin-resistant enterococci (VRE). What antibiotics can be used to treat this organism?

a.Synercid

Which of the following public health issues is uniting scientists from across the world to develop strategies to address it?

c.Antibiotic resistance

What broth is recommended in the tube dilution MIC tests?

b.

Mueller-Hinton

These antibiotics are cationic carbohydrate-containing molecules, and their positive charge provides the basis for their interaction with the 30S ribosomal subunit. What class of antibiotic are these?

c.

Aminoglycosides

Plasmids are

a.circular structures present in bacteria that contain genes encoding proteins and DNA and have the capacity to self-replicate and portion into daughter cells during cellular division.

The β-lactam agents consist of all the following antibiotics, except

a.

vancomycin.

In terms of MIC microdilution trays, a skipped well occurs

c.

when there is growth at higher concentrations and no growth at one or more of the lower concentration wells.

A zone of inhibition is

b.

the area around the antibiotic disk where the bacteria cannot grow.

Acquired antibiotic resistance mechanisms include

d.

All of the above

β-Lactamases hydrolyze β-lactam antibiotics using two distinct mechanisms: those having a metallo-based mechanism of action and those with

b.a serine-based mechanism of action.

When testing Escherichia coli, Klebsiella spp., and Proteus mirabilis, which drug is mostly likely to indicate the presence of an ESBL?

b.Cefpodoxime

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?

a.Kirby-Bauer

What is a breakpoint panel?

c.An MIC panel with only one or a few concentrations of each drug.

The members of the macrolide class of antibiotics include all the following, except

a.rifamycin.

What is the most critical step in any susceptibility test?

d.Inoculum preparation

Penicillins, cephalosporins, monobactams, and carbapenems all have this ring in their structure that is responsible for inhibiting the transpeptidation reaction, resulting in bacterial lysis and cell death.

b.

β-Lactam

If the MIC or zone size is interpreted as intermediate using the latest CLSI tables

c.

the patient's infecting organism is likely to require the maximum amount of antimicrobial or more than can be achieved and for which the clinical response is likely to be less than with a susceptible strain.

What automated system was originally designed for use in outer space?

d.

VITEK

When would it be appropriate for an institution to routinely test group C agents?

b.If a particular institution routinely encounters large numbers of isolates resistant to group A and group B agents

As a general guideline, it is suggested that within a particular antimicrobial class, primary (group A) agents should be reported first and secondary (group B) agents should be reported only if

c.the patient cannot tolerate the primary agents.

A primary tenet of antimicrobial therapy is to use

d.All of the above

Because the identity of the bacterial isolate is often unknown at the time the susceptibility testing is performed, it may include drugs that are inappropriate for reporting. What does the microbiologist do when this occurs?

a.

A drug should not be indiscriminately reported because results may be misleading.

In vitro testing conditions that can be modified to enhance the expression of oxacillin resistance include all the following, except

a.use Mueller-Hinton media.

Why should antimicrobial susceptibility testing of normal flora isolates or isolates likely to represent contamination or colonization not be performed?

a.

This may encourage a physician to treat a normal condition.

What antibiotics are active against ESBL-producing strains of bacteria?

c.

Carbapenems

Note that for some antimicrobial agents, different MIC interpretive criteria exist for

a.

organisms or organism groups.

What is the approximate final concentration of organisms in each well of a microdilution tray?

d.5 × 105 CFU/mL

What is the most widely used supplementary quality control measure for antimicrobial susceptibility testing?

b.

Use of antibiograms to verify results generated on patient isolates