Medical Laboratory Technician Exam Medical Laboratory Technician Clinical Microbiology 1

Question 1

A wound culture from a diabetic foot ulcer grows a Gram-positive coccus in clusters that tests positive for coagulase. The isolate is resistant to oxacillin. What is the most appropriate identification?

Accepted Answer

Methicillin-resistant Staphylococcus aureus (MRSA)

Answer

Coagulase-positive Gram-positive cocci in clusters are Staphylococcus aureus. Oxacillin resistance defines MRSA, which is clinically significant and requires contact precautions and specific antibiotic management.

Question 2

A CSF specimen from a patient with meningitis is sent for fungal culture. After 5 days at 30°C, a mucoid, cream-colored colony appears. India ink preparation reveals encapsulated yeast cells. What is the most likely organism?

Accepted Answer

Cryptococcus neoformans

Answer

Cryptococcus neoformans produces a characteristic polysaccharide capsule visible as a clear halo around yeast cells with India ink stain. It is the leading cause of fungal meningitis, especially in immunocompromised patients.

Question 3

A stool culture is plated on Hektoen enteric (HE) agar. After 24 hours, blue-green colonies with black centers are observed. Which organism is most likely responsible?

Accepted Answer

Salmonella typhimurium

Answer

Salmonella species produce blue-green colonies with black centers on HE agar due to hydrogen sulfide (H2S) production. Shigella produces green colonies without black centers; E. coli and Klebsiella are inhibited or produce salmon-colored colonies.

Question 4

A sputum culture from an immunocompromised patient grows a mold with septate hyphae that branch at 45-degree angles. Conidiophores bear chains of conidia from a single point. What is the most likely identification?

Accepted Answer

Aspergillus fumigatus

Answer

Aspergillus fumigatus produces septate hyphae with characteristic 45-degree branching. Its conidiophores terminate in a flask-shaped vesicle bearing phialides that produce chains of conidia. Rhizopus and Mucor have non-septate (coenocytic) hyphae.

Question 5

A throat swab from a patient with pharyngitis is plated on sheep blood agar. After 24 hours, a beta-hemolytic colony is observed. The isolate is catalase-negative, PYR-positive, and bacitracin-susceptible. What is the most likely organism?

Accepted Answer

Streptococcus pyogenes (Group A)

Answer

Streptococcus pyogenes (Group A Strep) is characteristically beta-hemolytic, catalase-negative, PYR-positive, and susceptible to bacitracin (A disc). Group B Strep is bacitracin-resistant, and Enterococcus is PYR-positive but not beta-hemolytic on sheep blood agar.

Medical Laboratory Technician Exam Practice Test

Medical Laboratory Technician Exam Practice Test

Medical Laboratory Technician Exam Medical Laboratory Technician Clinical Microbiology 1