Microbiology Rotation Exam

Differentiates GAS vs Enterococcus

PYR

PYR +

Enterococcus

PYR -

GAS

Differentiates Pseudomonas and E.coli/Kleb

OX

OX +

Pseudomonas

OX -

E.coli/ Kleb

Differentiates Staph aureus from other Staph sp

COAG

COAG +

Staph aureus

Coag -

Other Staph sp

Differentiates Staphs and Streps

CAT

CAT +

Staph

CAT -

Strep

CAT w+

Enterococcus

Requires incubation at 42^oC

Campylobacter

Martin Lewis agar contains…

Vancomycin

Legionella is cultured on which agar?

Martin Lewis

Which is the only Mycobacterium sp. that reduces nitrates?

M. tuberculosis

Which is the only Campylobacter sp. positive for Hippurate Hydrolysis?

C. jejuni

Mannitol salt agar is used to grow what organisms?

Strep sp.

What does Neisseria gonorrheae grow best on?

Modified Thayer Martin agar

Campylobacter jejuni requires which atmospheric condition for optimal growth?

Microaerophilic

Hektoen Enteric Agar is primarily used for recovery of:

Enteric gram-negatives (Salmonella, Shigella)

Lowenstein-Jensen medium is used to isolate

M. tuberculosis

Thayer Martin agar is selective for

N. gonorrhoeae and N. meningitidis

Triple Sugar Iron (TSI) agar differentiates organisms based on

Carbohydrate fermentation and H2S production

Mueller-Hinton agar is used for

Antimicrobial susceptibility testing

What is the primary dye in the Acid-Fast Staining procedure

Carbol fuchsin

Acridine orange stain is useful for

Detecting bacteria in sterile body fluids

Which organism is the best positive control for catalase testing

S. aureus

What is the best negative control for oxidase testing

Escherichia coli

The catalase test differentiates between

Staphylococci and Streptococci

The slide coagulase test detects

Bound coagulase

Lancefield grouping is based on

Cell wall carbohydrate antigens

MALDI-ToF MS identifies organisms by analyzing

Protein mass spectral fingerprints

16S sequencing is most useful when

All of the above

X factor is also known as

Hemin

V factor is also known as

NAD/NADP

An organism requiring BOTH X and V factors for growth is most likely

Haemophilus influenzae

When Staphylococcus aureus is streaked on blood agar alongside a fastidious organism such as Haemophilus influenzae, the fastidious organism often grows only near the Staph streak. Why is this?

Staph aureus secretes NAD (V factor), allowing H. influenzae to satellite around it

CHOC agar supports the growth of H. influenzae because

Heating releases X and V factors from RBCs

The indole test detects an organism’s ability to split indole from which amino acid?

Tryptophan

The reagent used in the spot indole test is:

DMACA

A positive indole test is MOST helpful in differentiating

All of the above

Why does Kovac’s reagent turn red in a positive indole test?

Indole reacts with DMAB

The PYR test detects

Pyrrolidonyl arylamidase

Positive PYR reaction

Red

PYR positive results are characteristic of

S. pyogenes

Besides GAS, which organism is also PYR +

Enterococcus sp.

The oxidase test detects

Cytochrome c oxidase

Positive oxidase test

Purple

Which organism is oxidase positive

Pseudomonas aeruginosa

Why must the oxidase test be read quickly?

The reagent auto-oxidizes

The catalase test detects the breakdown of

Hydrogen peroxide

The slide coagulase test specifically detects

Bound coagulase

The tube coagulase test detects

Free coagulase

An organism grows around a Staph streak on blood agar but not elsewhere. It does not grow on TSA alone. What does this suggest?

It requires V factor

You perform a spot indole test using DMACA reagent. The colony turns blue within seconds. This indicates

The microbe produces tryptophanase

A GPC is catalase negative and PYR positive. The organism is most likely

Strep pyogenes

A GPC in clusters, catalase+, coagulase- is most likely

Staph epidermidis

Micrococcus is different from Staph because Micrococcus

Is oxidase+, grows bright yellow colonies

A GPC that is catalase-, PYR+, and grows in 6.5% NaCl is most likely

E. faecalis

Strep pneumo looks like what on SBA

Alpha hem with sunken ‘coin’ shape

A GPR that is catalase+, large flat beta hem colonies, and ‘boxcar’ morphology is most likely

Bacillus cereus

Listeria monocytogenes can be distinguished by what characteristic?

Tumbling motility at 25^oC

Corynebacterium diphtheriae grows best on which medium

Cystine-tellurite agar

Gardnerella vaginalis typically shows what Gram stain morphology?

Gram-variable pleomorphic rods

Erysipelothrix rhusiopathiae can be identified by

H2S production in TSI

What produces H2S in TSI?

GPR

Gram-negative facultative anaerobes that ferment glucose is characteristic of what family?

Enterobacteriaceae

A K/A TSI, H2S positive suggests

Salmonella

Proteus mirabilis can be identified by which biochemical pattern

Urease positive

Shigella species are usually

Non-motile, NLF

Uropathogenic E. coli typically expresses which virulence factor?

P fimbriae

Kleb pneumo infections are associated with

Alcoholism

Yersinia enterocolitica grows best as

Cold enrichment

A NLF GNR that is oxidase+, grows at 42^oC and produces a fruity odor is likely

P. aeruginosa

Vibrio cholerae grows yellow colonies on what?

TCBS agar

Aeromonas species can be distinguished by which trait

Oxidase positive

Neisseria gonorrhoeae needs which atmosphere for best growth?

CO2

On a Gram stain, Neisseria appears as

Gram- diplococci

H. influenzae needs which factors for growth?

X and V

Which organism is part of the HACEK group?

Aggregatibacter actinomycetemcomitans

Haemophilus

The H in HACEK

Aggregatibacter

The A in HACEK

Cardiobacterium

The C in HACEK

Eikenella

The E in HACEK

Kingella

The K in HACEK

Moraxella catarrhalis is associated with which biochemial pattern

DNase+, butyrate esterase+

Growth in bile and resistance to kanamycin, vancomycin, and colistin is characteristic of

Bacteroides fragilis

Sulfure granules in draining lesions are characteristic of

Actinomyces israelii

Actinomycoses VS Nocardia

Anaerobic VS Aerobic and weak acid-fast

Lowenstein-Jensen and Middlebrook media are used for culturing

Mycobacteria

Runyon Group I produce pigment when

Exposed to light after incubation

A positive niacin test is characteristic of

M. tubercculosis

Which mycobacterium is strongly associated with cervical lymphadenitis in children

M. scrofulaceum

M. bovis and M. tuberculosis differ because M. bovis is

Niacin-, inhibited by TCH

Borrelia burgdorferi is a spirochete that causes

Lyme disease

The primary stage of syphilis is characterized by

Painless chancre

The secondary stage of syphilis presents with

Diffuse rash on palms and soles