Microbiology Flashcards

Which bacterial structure is the primary determinant of Gram stain results?

Answer: Peptidoglycan layer thickness

Gram-positive bacteria have a thick peptidoglycan layer that retains crystal violet, while Gram-negative bacteria have a thin layer that is decolorized.

A bacterium that can grow at refrigerator temperatures (4°C) is classified as a:

Answer: Psychrophile

Psychrophiles (cold-loving organisms) thrive at low temperatures ranging from -5°C to 20°C, with an optimum around 15°C.

Which mechanism allows bacteria to acquire antibiotic resistance genes from the environment through DNA uptake?

Answer: Transformation

Transformation involves uptake of naked DNA from the environment; naturally competent bacteria can incorporate these genes into their chromosome.

The Kirby-Bauer disk diffusion test measures:

Answer: Antibiotic susceptibility via zone of inhibition

The Kirby-Bauer test places antibiotic-impregnated disks on an inoculated agar plate; the diameter of the clear zone indicates susceptibility.

Which viral enzyme enables RNA viruses to replicate their genome without using DNA as an intermediate?

Answer: RNA-dependent RNA polymerase

RNA-dependent RNA polymerase (RdRp) uses an RNA template to synthesize new RNA strands, allowing RNA viruses to replicate independently of DNA.

Aspergillus fumigatus is an opportunistic pathogen that most commonly causes serious infections in patients with:

Answer: Severe neutropenia

Neutrophils are the primary defense against Aspergillus; severe neutropenia (as in chemotherapy patients) dramatically increases risk of invasive aspergillosis.

Which of the following is a characteristic feature of prions that distinguishes them from viruses?

Answer: They contain only protein and no nucleic acid

Prions are misfolded proteins (PrP^Sc) that lack nucleic acid entirely, yet can propagate by inducing normal proteins to misfold.