Micro- unit 5 quiz questions

On Day 2 of incubation, the primary aerobic and anaerobic plates of a wound aspirate show no growth, but the backup Thioglycollate broth is turbid near the bottom. What is the correct laboratory protocol?

-Discard the broth and report the culture as "No Growth"

-Re-incubate the original primary plates at 4°C for 7 days

-Report the broth as contaminated with normal skin flora without further testing

-Perform a Gram stain on the turbid broth and subculture it onto both aerobic and anaerobic agar plates

Perform a Gram stain on the turbid broth and subculture it onto both aerobic and anaerobic agar plates

What is the primary diagnostic purpose of performing a direct Gram stain on a wound culture specimen?

-To determine the exact antimicrobial susceptibility profile of pathogens

-To measure the total pH of the tissue exudate

-To replace the need for subculturing onto primary agar media

-To differentiate active host tissue infection from superficial skin colonization

To differentiate active host tissue infection from superficial skin colonization

What is the functional role of Enriched Thioglycollate Broth (THIO) in a primary wound culture setup?

-It selectively inhibits Gram-positive cocci while promoting fungal spore germination

-It acts as a primary differential medium for lactose fermentation

-It neutralizes all residual antibiotics present in the patient's serum sample

-It serves as a backup enrichment liquid medium with an oxygen gradient supporting aerobes, facultative organisms, and anaerobes

It serves as a backup enrichment liquid medium with an oxygen gradient supporting aerobes, facultative organisms, and anaerobes

All of the following are examples of non-culture based assays to detect pathogens in wound, skin and soft tissue infections, except:

-Ab/Ag Detection

-MALDI-TOF

-BBE

-PCR

BBE

A superficial wound swab from a foot ulcer yields moderate Gram-positive cocci and many Gram-negative rods on culture, but the direct Gram stain showed >25 squamous epithelial cells per low-power field and <5 PMNs. How should the laboratory handle organism workup?

-Perform full identification and antimicrobial susceptibility testing on all isolated organisms

-Perform anaerobic susceptibility testing on the Gram-positive cocci

-Immediately call a critical panic value to the attending physician

-Report as "Mixed skin flora / superficial contamination; re-collection recommended if clinical infection is suspected"

Report as "Mixed skin flora / superficial contamination; re-collection recommended if clinical infection is suspected"

Which selective components in MacConkey agar inhibit Gram-positive organisms while allowing Gram-negative bacilli to grow?

-Phenylethyl alcohol and hemin

-Vancomycin and nystatin

-Bile salts and crystal violet

-Colistin and nalidixic acid

Bile salts and crystal violet

Under which atmospheric condition should primary 5% Sheep Blood Agar and Chocolate Agar plates inoculated with wound specimens be incubated?

-Microaerophilic container with 5% O2 at 25°C

-Ambient room air at 22°C

-5% to 10% CO2 at 35°C–37°C

-Anaerobic jar at 42°C

5% to 10% CO2 at 35°C–37°C

Which specimen type is considered optimal for the microbiological recovery of deep tissue wound pathogens?

-Surface swab of intact skin adjacent to the wound

-Deep needle aspirate of purulent exudate or tissue biopsy

-Dry cotton swab taken from superficial crusts

-Swab collected from an uncleaned decubitus ulcer

Deep needle aspirate of purulent exudate or tissue biopsy

What is the primary selective purpose of Colistin-Nalidixic Acid (CNA) agar in a primary wound culture workup?

-Differentiating lactose fermenters from non-lactose fermenters

-Suppressing fungal growth in deep wound tissue samples

-Inhibiting Gram-positive cocci while growing enteric bacilli

-Inhibiting Gram-negative bacilli to selectively isolate Gram-positive bacteria

Inhibiting Gram-negative bacilli to selectively isolate Gram-positive bacteria

A patient with severe post-traumatic gas gangrene has a wound aspirate direct Gram stain showing large boxcar-shaped Gram-positive rods, but NO white blood cells are seen. What explains this microscopic finding?

-Heat fixation completely dissolved all host white blood cells

-The specimen was collected from an uninfected healing site

-Clostridium perfringens alpha-toxin (lecithinase) lysed host leukocytes in the infected tissue

-The patient has severe congenital neutropenia

Clostridium perfringens alpha-toxin (lecithinase) lysed host leukocytes in the infected tissue

Which selective medium containing vancomycin, colistin, nystatin, and trimethoprim is used to isolate Neisseria gonorrhoeae from cutaneous or wound lesions?

-Modified Thayer-Martin (MTM) Agar

-Columbia CNA Agar

-MacConkey Agar

-Sabouraud Dextrose Agar

Modified Thayer-Martin (MTM) Agar

When a wound specimen transport delay exceeds 15 to 30 minutes, what action is necessary to prevent drying and maintain organism viability?

-Storing the specimen uncovered in an ice bath

-Adding 10% formalin solution to the specimen container

-Heating the container to 45°C in a dry bath

-Placing the specimen into an appropriate transport medium system

Placing the specimen into an appropriate transport medium system

On Day 2 of incubation, the primary aerobic and anaerobic plates of a wound aspirate show no growth, but the backup Thioglycollate broth is turbid near the bottom. What is the correct laboratory protocol?

-Perform a Gram stain on the turbid broth and subculture it onto both aerobic and anaerobic agar plates

-Report the broth as contaminated with normal skin flora without further testing

-Re-incubate the original primary plates at 4°C for 7 days

-Discard the broth and report the culture as "No Growth"

Perform a Gram stain on the turbid broth and subculture it onto both aerobic and anaerobic agar plates

A patient with severe post-traumatic gas gangrene has a wound aspirate direct Gram stain showing large boxcar-shaped Gram-positive rods, but NO white blood cells are seen. What explains this microscopic finding?

-Heat fixation completely dissolved all host white blood cells

-The specimen was collected from an uninfected healing site

-Clostridium perfringens alpha-toxin (lecithinase) lysed host leukocytes in the infected tissue

-The patient has severe congenital neutropenia

Clostridium perfringens alpha-toxin (lecithinase) lysed host leukocytes in the infected tissue

A direct Gram stain of a deep surgical wound aspirate demonstrates many PMNs and abundant Gram-negative bacilli, but after 24 hours of aerobic incubation, no growth is observed on Blood or MacConkey agars. What is the most appropriate evaluation of these findings?

-The Gram stain was falsely positive and should be disregarded

-The specimen was contaminated with normal skin flora during draw

-The unrecovered bacilli are likely obligate anaerobes requiring continued anaerobic incubation

-The patient has a viral infection and media was inoculated incorrectly

The unrecovered bacilli are likely obligate anaerobes requiring continued anaerobic incubation

Which specimen type is considered optimal for the microbiological recovery of deep tissue wound pathogens?

-Surface swab of intact skin adjacent to the wound

-Swab collected from an uncleaned decubitus ulcer

-Dry cotton swab taken from superficial crusts

-Deep needle aspirate of purulent exudate or tissue biopsy

Deep needle aspirate of purulent exudate or tissue biopsy

What is the functional role of Enriched Thioglycollate Broth (THIO) in a primary wound culture setup?

-It acts as a primary differential medium for lactose fermentation

-It selectively inhibits Gram-positive cocci while promoting fungal spore germination

-It serves as a backup enrichment liquid medium with an oxygen gradient supporting aerobes, facultative organisms, and anaerobes

-It neutralizes all residual antibiotics present in the patient's serum sample

It serves as a backup enrichment liquid medium with an oxygen gradient supporting aerobes, facultative organisms, and anaerobes

Mannitol Salt Agar (MSA) differentiates Staphylococcus aureus from coagulase-negative staphylococci based on which chemical reaction?

-Production of green pigment on nutrient agar

-Fermentation of mannitol causing the phenol red indicator to turn yellow

-Lysis of red blood cells producing a clear zone around colonies

-Hydrolysis of esculin turning the agar black

Fermentation of mannitol causing the phenol red indicator to turn yellow

A superficial wound swab from a foot ulcer yields moderate Gram-positive cocci and many Gram-negative rods on culture, but the direct Gram stain showed >25 squamous epithelial cells per low-power field and <5 PMNs. How should the laboratory handle organism workup?

-Report as "Mixed skin flora / superficial contamination; re-collection recommended if clinical infection is suspected"

-Perform anaerobic susceptibility testing on the Gram-positive cocci

-Perform full identification and antimicrobial susceptibility testing on all isolated organisms

-Immediately call a critical panic value to the attending physician

Report as "Mixed skin flora / superficial contamination; re-collection recommended if clinical infection is suspected"

Under which atmospheric condition should primary 5% Sheep Blood Agar and Chocolate Agar plates inoculated with wound specimens be incubated?

-Anaerobic jar at 42°C

-Ambient room air at 22°C

-Microaerophilic container with 5% O2 at 25°C

-5% to 10% CO2 at 35°C–37°C

5% to 10% CO2 at 35°C–37°C

This condition is often seen in children, historically from Group A strep, but now the predominant pathogen is S. aureus, often MRSA:

-Erysipelas

-Folliculitis

-Impetigo

-Paronychia

Impetigo

Normal skin flora include all of the following except:

-Candida albicans

-Micrococcus species

-Bacillus species (not anthracis)

-Corynebacterium jeikeium

Corynebacterium jeikeium

Normal ear flora include all of the following except:

-Propionibacterium sp.

-Coag Neg Staph

-S. pneumoniae

-Alpha Strep

S. pneumoniae

This gram negative pathogen is associated with human bites most commonly:

-Vibrio vulnificus

-Stenotrophomas maltophilia

-Eikenella corrodens

-Aeromonas hydrophilia

Eikenella corrodens

A wound culture swab from an uncleaned decubitus ulcer yields moderate coagulase-negative Staphylococci, diphtheroids, and Cutibacterium acnes. The direct Gram stain demonstrates abundant squamous epithelial cells and very few PMNs. How should the laboratory specialist evaluate these findings?

-Fungal wound infection requiring specialized mycology media

-Active deep tissue infection caused by polymicrobial pathogens

-Nosocomial infection requiring immediate systemic antimicrobial therapy

-Superficial skin colonization and contamination due to improper collection

Superficial skin colonization and contamination due to improper collection

This skin infection causes painful erythema, warmth, and edema of the skin with poorly defined margins. Common pathogens include S. aureus and S. pyogenes:

-Bullous Impetigo

-Cellulitis

-Impetigo

-Erysipelas

Cellulitis

A surgical wound aspirate from a patient with a jaw abscess and 'sulfur granules' in the purulent discharge yields non-acid-fast, branching Gram-positive rods that form 'molar tooth' colonies after 7 days of anaerobic incubation. What organism is indicated by these findings?

-Mycobacterium marinum

-Actinomyces israelii

-Nocardia asteroides

-Cutibacterium acnes

Actinomyces israelii

This organism causes tularemia and regional lymph node enlargement:

-Eikenella corrodens

-Capnocytophaga species

-Stenotrophomonas maltophilia

-Francisella species

Francisella species

This gram negative pathogen is associated with animal bites and scratches most commonly:

-Pasteurella multiocida

-Corynebacterium sp

-Eikenella corrodens

-Lactobacillus sp

Pasteurella multiocida

An example of a gram positive pathogen in a wound culture is:

-Candida albicans

-Group A Streptococcus

-Cutibacterium acnes

-Viridans Streptococcus

Group A Streptococcus

Gas gangrene is caused by:

-S. aureus

-C. perfringens

-Enterobacteriaceae

-S. pyogenes

 

C. perfringens

An agricultural worker suffers a deep traumatic wound to the thigh and develops severe localized pain and gas crepitus within 24 hours. A direct Gram stain of the wound aspirate shows large boxcar-shaped Gram-positive rods, but host leukocytes are completely absent. What pathophysiological mechanism explains the absence of leukocytes?

-The specimen was contaminated with resident Cutibacterium acnes

-Clostridium perfringens alpha-toxin (lecithinase) lysed the host leukocytes

-The patient has an inherited immunodeficiency preventing PMN migration

-Methanol fixation dissolved all white blood cells on the slide

Clostridium perfringens alpha-toxin (lecithinase) lysed the host leukocytes

A veterinary technician develops rapid erythema, swelling, and purulent exudate 12 hours after sustaining a deep cat bite. Culture of the wound aspirate yields small Gram-negative coccobacilli that grow well on Sheep Blood Agar and Chocolate Agar with a distinct musty odor, but fail to grow on MacConkey agar. Biochemical testing is positive for oxidase, catalase, and indole. What is the identity of this pathogen?

-Eikenella corrodens

-Pasteurella multocida

-Capnocytophaga canimorsus

-Pseudomonas aeruginosa

Pasteurella multocida

A patient who sustained a puncture wound in a saltwater bay presents with rapidly progressive cellulitis and hemorrhagic bullae. Culture of the wound aspirate yields curved Gram-negative rods that ferment glucose, test oxidase-positive, and require sodium chloride (NaCl) for growth. What is the most likely pathogen?

-Vibrio vulnificus

-Pasteurella multocida

-Aeromonas hydrophila

-Eikenella corrodens

Vibrio vulnificus

Normal eye flora include all of the following except:

-Propionibacterium sp.

-S. aureus

-Alpha Strep

-Coag Neg Staph

S. aureus

Normal skin flora include all of the following except:

-Micrococcus species

-Corynebacterium jeikeium

-Bacillus species (not anthracis)

-Candida albicans

Corynebacterium jeikeium

A 4-year-old child presents with superficial facial vesicles that have ruptured and formed golden, honey-colored serous crusts. The predominant pathogen isolated from the lesion is catalase-positive, coagulase-positive Gram-positive cocci in clusters. What is the diagnosis and primary virulence factor involved?

-Erysipeloid caused by Erysipelothrix rhusiopathiae neuraminidase

-Bullous pemphigoid caused by Streptococcus agalactiae hyaluronidase

-Impetigo caused by Staphylococcus aureus producing exfoliative toxin

-Erysipelas caused by Streptococcus pyogenes M protein

Impetigo caused by Staphylococcus aureus producing exfoliative toxin

This skin infection causes painful erythema, warmth, and edema of the skin with poorly defined margins. Common pathogens include S. aureus and S. pyogenes:

-Cellulitis

-Erysipelas

-Impetigo

-Bullous Impetigo

Cellulitis

An example of a glucose non-fermenter, gram negative pathogen in a wound culture is:

-Capnocytophaga species

-Eikenella corrodens

-Alcaligenes sp

-Aeromonas hydrophilia

Alcaligenes sp

A 65-year-old diabetic patient presents with a malodorous, necrotic foot ulcer. A needle aspirate yields pleomorphic Gram-negative rods that form dark brown-to-black colonies on Bacteroides Bile Esculin (BBE) agar and are resistant to 20% bile. Aerotolerance testing demonstrates growth only on the anaerobic blood agar plate. What is the organism's identity?

-Pseudomonas aeruginosa

-Bacteroides fragilis group

-Clostridium perfringens

-Fusobacterium nucleatum

Bacteroides fragilis group