MLS 2022 FALL MICRO Test 1 Review

A dense, internal structure formed by some bacteria to withstand unfavorable environmental conditions is a:

Spore

A substance added to culture media to prevent growth of certain bacteria is:

An inhibitor

A medium, which inhibits the growth of some organisms and supports the growth of others, is:

Selective

Endotoxins are usually associated with:

Gram negative bacteria

The primary safety violation when a technologist has become infected with an agent from a specimen is:

Creating an aerosol

Capsules are one of the factors controlling virulence because they:

Protect the bacterium from phagocytosis

A consideration for collection and handling of specimens would be:

Using sterile technique in collecting the specimen

Blood may be added to culture media as an enrichment and is also used as an indicator of:

Hemolysis

Which of the following statements is true:
most of the time we can live in peaceful coexistence with microorganisms capable of producing overt disease, if our normal host defenses are penetrated and bacteria gain access to tissues not normally infected, there is a significant probability of overt disease, the presence of relatively non virulent bacteria at a given body site often prevents colonization by more virulent species

All of the above

While working in the laboratory a heavy amount of infectious agent is spilled on your cloth lab coat. The appropriate action would be to:

Remove it and autoclave it

QC procedure in a microbiology laboratory must include:

Sterility testing of all media, reagents, stains, monitoring temperatures

Which of the following could be fomites: bedpans, sheets, tourniquets, tables

All of the above

Bacteria with a strict metabolic requirement for oxygen could conceivably be which of the following

Obligate aerobe

Criteria for rejection of a sample for culture is/are:

Improperly labeled or leaky specimens

A general consideration for collection and handling of specimens would be:

Collect from a site that is representative of the infection

Most blood agar media utilizes which type and concentration of blood:

5% sheep blood

When preparing direct smears, the best part of the specimen to use is:

Blood, mucus, pus

Sputum specimens must be assessed for quality by:

Counting the numbers of epithelial cells per lpf

A direct smear may assist the lab scientist to

Determine the quality of the specimen

A direct smear may assist the medical lab scientist to

Know what organisms are expected to grow

Properly preserved specimens for transport to the lab may prevent which of the following:

Loss of organisms due to drying, changes in pH or temperature

The bacterial structure that is usually composed of polysaccharides and affords protection from phagocytosis is the:

Capsule

Identify Micrococcus sp.

- Is normal flora on skin

- yellow to off-white
color colonies

- is strict anaerobe

- gram positive cocci in clusters

Tests:
Modified Oxidase - Pos
Resist. to Bacitracin- sensitive
Catalase - Pos
Coag - Neg

Identify Staphylococcus sp.

- gram positive cocci

- aerobic or facultatively anaerobic

- medium sized, cream-colored, white, or light gold, buttery-looking

Tests:
Modified Oxidase-Neg
Resist. to Bacitracin- Resistent
Catalase - Pos
Coag - Pos

Safety Hazards and Procedures

- Prevent aerosolization
- Flame loops frequently
- Don't sniff the plates directly
- Use sterile technique
- Dispose of used utensils and plates appropriately
- Autoclave contaminated materials if possible
- Soak contaminated surfaces in 10% bleach for 15-20 min

Specimen collection and rejection

- Collect from an area representative of infection
- Collect using sterile technique
- Reject if specimen is leaking, improperly labeled, improperly stored, improperly collected

Endotoxins

gn bacteria

Exotoxins

gp bacteria

Spores

protect bacteria from harsh environments

Pili and fibriae

nonflagellar, proteinaeious, hairlike appendages that adhere bacterial cells to one another and to host cells

Flagellum

locomotion

Capsules

polysaccharide polymers, may be polypeptides. Helps the pathogen evade phagocytosis. Removed by boiling suspension.

What does an inhibitor do in the media?

- Inhibitor prevents growth of certain species of bacteria, but can grow other species; not necessarily selective (able to grow one certain species)

- Use is to prevent growth of an already-identified bacteria or normal flora

Streptococcus pneumoniae

Gp cocci in pairs or short chains, lancet shaped

Alpha hemolysis on SBA, round, mucoid, dome-shaped appearance

Tests: Catalase neg, alpha hemolysis, P disk sensitive, PYR neg, BEA neg

Diseases: Causes pneumonia, sinusitis, otitis media, bacteremia, meningitis

Enterococcus/Streptococcus Grp D

Tests: Catalase neg, alpha, beta or nonhemolytic, PYR pos, BEA pos

Enterococcus grows in 6.5% NaCl

Diseases: UTIs, bacterial endocarditis, sepsis from contaminated xenografts in burn patients, infection of the CNS

Streptococcus Grp B - Streptococcus Agalactiae

SBA with grayish white mucoid colonies, gp cocci in chains

Tests: Catalase neg, beta or nonhemolytic, A skis R, PYR neg, BEA neg, CAMP pos, HIPP pos

Diseases: neonatal disease due to presence in vaginal tract

Streptococcus Grp A - Streptococcus Pyogenes

On blood agar, small translucent, beta hemolytic

Tests: Catalase neg, A disk S, PYR pos, BEA neg

Diseases: Bacterial pharyngitis, impetigo, erisipelas, cellulitis, scarlet fever, necrotizing fascitis, Streptococcal toxic shock syndrome, rheumatic fever, acute glomerulonephritis

Staphylococcus saprophyticus

Colonies are larger, 50% of strains produce yellow pigment

Is resistant to novobiocin in urine isolates

Tests: Coag negative , dextrose fermentation pos, novobiocin resistance R

Staphylococcus epidermidis

Colonies are small- to medium-sized, nonhemolytic (can be weakly hemolytic), gray-to-white

Tests: Coag negative, dextrose fermentation pos, novobiocin resistance S (in urine samples)

Diseases: Is normal skin flora, but can be source of hospital-acquired infection (catheters, UTIs)

Staphylococcus aureus

Gram-positive cocci, coagulase-positive

Colonies are round, smooth, white, creamy. Can produce hemolytic zones. May exhibit yellow pigment

Grow on SBA (use high NaCl concentration to be selective for Staph)

Enterotoxins produced by 30-50% of aureus isolates

Diseases: toxic shock syndrome (TSST-1), Ritter disease (exfoliative toxin), folliculitis, furuncles, impetigo, Scalded Skin Syndrome, food poisoning, osteomyelitis, septic arthritis, and prosthetic joint infections

Which of the following would affect the results of a disc diffusion susceptibility test by making the organism appear more resistant?

Too many organisms in the inoculum

Antibiotics that act by inhibiting synthesis of the bacterial cell wall include:

Penicillin, methicillin, cephalosporins

The ratio of the amount of antimicrobial that is toxic to the amount, which is effective, is known as:

The therapeutic index

Staphylococcus aureus would most likely be resistant to:

Penicillin

Staphylococcus epidermidis is:

occasionally pathogenic in wounds, bacteremia, and prosthetic valve and joint infections

You have isolated a yellow colony on 5% sheep blood agar. A gram stain shows the organism to be large gram positive cocci in clusters. Subsequent tests yield the following results: catalase +, Tube coag =, slide coag =, does not ferment glucose. The organism is:

Micrococcus sp.

The test used to differentiate a Micrococcus species from a Staphylococcus species, is:

Ability to ferment glucose

The definitive test for the differentiation of Staphylococcus aureus from other Staphyloccocus species is:

Coagulase test

The ability to produce the enzyme coagulase is used as a means of identifying:

Staphylococcus aureus

The following results were observed on a gram positive coccus isolated from a wound specimen: coag at 4 hrs = +, novobiocin = 5 mm, hemolysis on BAP = beta, DNase = +, Mannitol salt Agar = +. What is the most probable identification?

Staph aureus

What body site is Strep pneumoniae part of the normal flora.

Respiratory tract

Which of the following is characteristic of Streptococcus pyogenes?

Bacitracin sensitive

Streptococcal Toxic Shock Syndrome, characterized by a bright red, sandpaper-textured rash is caused by:

Gp A Strep

Colonies of Streptococcus pneumoniae on blood agar would most closely resemble colonies of:

Streptococcus viridans group

The optochin (ethylhydrocupreine hydrochloride) identification test consists of placing optochin discs on blood agar plates heavily inoculated with the suspected organism. If there is a zone of inhibition of > 14 mm surrounding the disc following overnight incubation at 35ºC, the colony most likely is:

Streptococcus pneumoniae

Streptococcus pneumoniae may be differentiated from alpha hemolytic streptococci on the basis of the:

Optochin disc test

To differentiate Streptococcus pneumoniae from alpha hemolytic streptococcus viridans group:

Perform an optochin disc test

Blood culture (two) on a newborn grew beta-hemolytic strep with the following reactions: CAMP test = +, hippurate hydrolysis = +, bile solubility = 0, 6.5% NaCl = 0, PYR = 0, bile esculin = 0, Bacitracin = R, SXT = R. What is the most likely identification?

Gp B strep

The identification of Enterooccus is based on which test(s)?

Hydrolysis of bile esculin and PYR positive

Differentiation of Enterococcus species from group D, non-enterococcus species, is important because:

Enterococci are often resistant to penicillin, the drug of choice for streptococcal infections

A procedure, which directly determines beta-lactamase production by a microorganism, is based on detection of:

Color change resulting from the breaking of beta-lactam ring of a chromogenic cephalosporin

Which of the following is (are) commonly tested for beta-lactamase production:

Haemophilus influenzae

List a disease caused by Staphylococcal toxins

Toxic shock syndrome

Why is it necessary to distinguish Staph aureus from coagulase negative Staph infections?

Staph aureus infections can be much more invasive

Select the most appropriate test(s) and result(s), which would differentiate Staph epidermidis from Staph. Saprophyticus.

Novobiocin sensitive

____________ is used to determine catalase reaction.

Hydrogen peroxide

Staphylococcus epidermidis is characterized by:

Coagulase negative

False positive catalase tests may result from:

Picking up agar from the blood plate

What areas of the body harbor staph aureus as part of its normal microbial flora?

Nose & skin

Which of the following is (are) useful in identifying group B streptococcus?

Camp test positive, hippurate positive

The characteristic test which BEST distinguishes staphylococci from streptococci is the:

Catalase test

A beta hemolytic Streptococcus is isolated from a throat culture. Which of the following tests would be of most value to the physician in evaluating the significance of the microorganism?

Bacitracin disc

Streptococcal toxic shock syndrome produces a bright red rash due to production of:

Exotoxin

The identification of Enterooccus is based on which test(s)?

Hydrolysis of bile esculin and PYR positive

The gram stain morphology of Streptococcus pneumoniae is described as:

Gram positive lancet shaped diplococci

Which of the following is characteristic of Streptococcus pyogenes?

Bacitracin sensitive

Which of the following best describes Group B Streptococcus

gram positive cocci, beta hemolytic, catalase negative, bacitracin resistant, CAMP positive

Differentiation of Enterococcus species from group D, non-enterococcus species, is important because:

Enterococci are more often implicated in disease

A positive Beta lactamase test indicates

Resistance to penicillin

Which of the following statements concerning the beta lactamase test is FALSE

a negative test for beta-lactamase always correlates with sensitivity to Gentamicin

Staph aureus is generally resistant to Penicillin G by what mechanism?

Beta lactamase production

List the types of infections caused by Staph aureus:

Impetigo, boils, wound infections

Under appropriate conditions of cultivation S. pneumoniae and alpha streptococcus give the same kind of hemolytic reaction on blood agar. Which of the following best describes this type of hemolytic activity?

Incomplete hemolysis–greening

Necrotizing fasciitis is an extremely serious, rapidly progressing infection of the fascia caused by:

Gp A Strep

A negative PYR test is helpful in identifying which of the following?

Gp D non-Enterococcus, Gp B Beta hemolytic Strep