MICROB FINAL

Which virulence factor allows Streptococcus pneumoniae to evade phagocytosis by host immune cells?

Polysaccharide capsule

What is the primary role of Gram's iodine in the Gram stain procedure?

It acts as a mordant to form a complex with crystal violet

Which type of testing uses a known antibody to detect an "unknown" antigen in a patient's direct specimen?

Immunoassay

Which specialized media is used to detect small numbers of aerobes and anaerobes by supporting growth throughout a tube?

Thioglycolate broth

inhibit Gram-positive bacteria while promoting Gram-negative bacteria also testing lactose fermentation

MAC

A urine specimen is delayed for 3 hours and refrigerating the sample was not an option. What is the appropriate transport preservative that should have been used?

boric acid

If a physician orders a "Screening Culture" for Group A Streptococcus, the laboratory will:

Report only the specific pathogen requested (Streptococcus pyogenes)

Which enzyme is responsible for the "spreading factor" that breaks down host extracellular matrix to aid in deeper invasion?

Hyaluronidase

A beta-hemolytic Streptococcus is isolated from a throat swab. It is sensitive to bacitracin (Taxo A) and PYR-positive. What is the presumptive identification?

Streptococcus pyogenes (Group A

An isolate is catalase-positive, coagulase-negative, and PYR-positive. Which organism should be suspected, especially if it is also positive for ornithine decarboxylase?

Staphylococcus lugdunensis

A 22-year-old female presents with symptoms of a urinary tract infection. The urine culture grows a catalase-positive, coagulase-negative Gram-positive coccus. Which test result would identify the isolate as Staphylococcus saprophyticus?

Resistant to Novobiocin

inhib gram neg pro gram pos

CNA or PEA

An isolate from an infected prosthetic heart valve is cat pos, coag neg, microdase neg, S to novobiocin

Staph epidermidis using Biofilm formation

Which test result helps differentiate Group D Streptococcus from Enterococcus species?

Growth in 6.5% NaCl broth

Which of the following Streptococcus species is PYR-positive?

streptococcus pyogenes

Which mechanism allows Staphylococcus aureus to evade the immune system by binding the Fc portion of IgG?

protein A

K antigen

capsule

metallic green sheen on Eosin Methylene Blue (EMB) agar

e coli

Which of the following organisms is considered an overt/primary pathogen that is always significant if isolated?

salmonella

muccoid on MAC, VP positive, Citrate positive, and Indole positive. Which organism is most likely present?

Klebsiella oxytoca

When interpreting XLD agar, a red colony with a black center most likely indicates which pathogenic organism?

salmonella

required for the decarboxylase (LDC, ODC, ADC) tests

An acidic environment produced by glucose fermentation

GNR, beta on BAP, lactose fermenter MAC, indole pos, nitrate pos, MR pos, motile

e coli

nitrate reaction

clear after reagent and after zinc= pos

clear after reagents and red after zinc= neg

In the Simmons' citrate test, what causes the medium to change from green to blue?

Production of ammonia from the use of ammonium salts.

What is the primary purpose of the ONPG test in a clinical microbiology laboratory?

To detect "late" or delayed lactose fermentation in organisms lacking permease.

Which branch of microbiology specifically studies fungi?

mycology

A "screening culture" is defined as a culture that:

reports only specific pathogens from a specific source

What are the standard incubation conditions for most bacteria and yeast in a culture?

18-24 hrs 35-37 C

How is the reaction visualized in many antigen detection immunoassays?

color

Which of the following is an organism often detected via molecular diagnostics?

WNV w nile virus

What is the standard safety requirement and overall best choice for processing microbiology specimens?

bio safety hood

Stuart’s or Amie’s media are common transport media for

swabs

Level 3 priority specimens are those that require:

Quantification (urine)

What is the preferred transport medium for stool specimens?

cary-blair with SPS sodium polyanethol sulfate

Unpreserved specimens such as tissue, sputum, and feces fall into which priority level?

2

A specimen transport time exceeding how many hours is a typical criterion for rejection if the specimen is not preserved?

2 hrs

Physical method of disinfec

UV light, pasteurization, boiling

Which gas is the largest component of the atmosphere in an anaerobic incubator?

N 85-90

When inoculating multiple plates, what is the correct order of inoculation?

Non-selective media first, then selective

How long must records for media quality control be maintained by the laboratory?

2 years

Which medium inhibits most organisms except for Staphylococcus?

MSA

Which technique is used to kill normal flora in a specimen when looking for a specific organism like Mycobacteria?

decontaimination

What is the required humidity level for most incubators to prevent evaporation?

70-80

an organism that requires reduced oxygen and increased CO2 to grow

Microaerophile

What is the typical incubation length for anaerobic cultures?

5-6 days

Which type of media contains complex substances like blood or growth factors specifically for fastidious organisms?

enriched

Which type of cell in a direct specimen is characterized by a multiple-lobed nucleus?

 WBC or polymorphonuclear (PMN)

GNCB

tiny, short rods almost spherical

yeast gram stain

pos, larger than cocci

When scanning a direct specimen slide, how many fields should be checked to assess the quality?

10-30

In which group of bacteria are spores typically observed?

gram pos

Which reagent acts as the decolorizer?

acetone or alc

Gram-negative cell lysis, systemic effect on the host due to the release of its cell wall components?

fever and complement activation

Which component of the Gram-negative bacterial cell wall serves as an endotoxin?

lipid A

exotoxins

heat liable, excreted by living cells

How is the virulence of a microorganism typically measured in a clinical context?

By the number of microorganisms needed to cause an infection, low = highly virulent

protease as exotoxin

destroys extracellular structures

How do indigenous normal flora protect the host from colonization by pathogenic bacteria?

by competing for nutrients and space on receptor sites

normal flora “priming“

stimulates the production of natural antibodies for a rapid response

A patient undergoing chemotherapy develops a Candida species infection. What is the most likely reason for this?

chemo disrupted balance of normal flora

Which organism is classified as a "definite pathogen" because it is not part of normal flora and always causes disease?

vibrio cholera

Which sterile fluid surrounds the fetus during pregnancy?

anmiotic

Which stain is commonly used to detect the presence of fecal leukocytes?

meth blue stain

purpose of performing a direct microscopic examination of a clinical specimen

assess quality of the specimen

an example of an acid-fast stain

kinyoun stain

advantage of fluorochrome stains over traditional acid fast

enhanced detection and higher sensitivity

microscopic exam for motility

hanging drop

Micrococcus vs CNS oxidase

pos, neg

gamma, bile esculin pos, 6.5% NaCl pos

enterococcus sp

optochin S

s. pneumoniae

beta, cat neg, PYR pos

group A strep

If an isolate is beta-hemolytic, PYR-negative, and Hippurate-negative, what information is required to evaluate if further testing (BE and salt) is necessary?

source of organism

The PathoDx or StrepTEX Streptococcal Grouping Test detect

group specific carb ags from the cell wall

alpha, optochin R, bile esculin neg, 6.5 NaCl neg

virdans group strep

differentiates Group B strep from other beta-hemolytic, PYR-negative streptococci

hippurate hydrolysis (pos)

enterobacterals nitrate test

reduce to nitrite

perform a decarboxylase test (e.g., Lysine, Ornithine), the organism must be able to:

ferment glucose

LDC pos ODC neg

kleb pneu

MacConkey (SMAC) agar is a selective and differential medium used primarily to screen stool specimens for:

e coli O157

pink MAC, H2S pos

citrobacter freudii

Bacillus anthracis exotoxins- protective ag PA and lethal factor LF

binds and opens the target cell to allow other factors to enter

causes cell death

Gardnerella vaginalis beta on

HBT

3% KOH test

no tread with GPR

cat neg, alpha or gamma, GPR from skin lesion, H2S in TSI, non motile

Erysipelothrix rhusiopathiae

palisading V L, diptheroids, club-shaped GPR, non motile, cat +

Corynebacterium species

non pathogenic bacillus

motile and beta

oxidase pos, GNDC from resp, hockey puck, butyrate esterase pos (bluegreen), nitrate reduc, DNase

moraxella catarrhalis

In a DNase test, a clear halo around the inoculation line indicates that the organism:

Produces extracellular enzymes that hydrolyze DNA.

Moraxella catarrhalis is distinguished from Neisseria species by its ability to

reduce nitrate and produce DNase

MTM grow, oxidase pos, use glucose maltose and lactorse in CTA, what causes use of lactose

Beta-D-galactosidase

CTA only glucose yellow

n. gonorrhoeae

BGAL B-D-galactodase pos or GLUT pos

n. lactamica

Jembec system

enriched selective media transport with CO2 for capnophilic growth

GNDC in CSF, oxidase pos, GLUT pos, PRO variable

n. meningitidis

IgA1 protease in neisseria

increase invasiveness by cleaving abs on mucosal surfaces

CTA n. meningitidis

yellow for glucose and maltose, red for lactose and sucrose

In the Porphyrin test, the organism converts the substrate ALA (delta-aminolevulinic acid) into:

prophyrins and porphobilinogen

factor V

Nicotinamide-adenine dinucleotide (NAD)