Microbiology: Microbial Ecology and Pathogenesis Flashcards

Which virulence factor allows Streptococcus pyogenes to resist phagocytosis by white blood cells?

Answer: M protein

The M protein on the surface of S. pyogenes inhibits complement activation and opsonization, thereby resisting phagocytosis.

In the sulfur cycle, which process converts sulfate (SO₄²⁻) back to hydrogen sulfide (H₂S) under anaerobic conditions?

Answer: Sulfate reduction

Sulfate-reducing bacteria such as Desulfovibrio use sulfate as a terminal electron acceptor under anaerobic conditions, producing H₂S.

Quorum sensing in bacteria refers to:

Answer: Cell-density-dependent regulation of gene expression via chemical signals

Quorum sensing allows bacteria to coordinate behavior — such as biofilm formation or toxin production — by detecting population density via autoinducer molecules.

Which of the following best defines 'pathogenicity'?

Answer: The ability of a microorganism to cause disease in a host

Pathogenicity is the inherent ability of a microorganism to cause disease, distinguishing pathogens from non-pathogens.

Horizontal gene transfer via direct cell-to-cell contact through a sex pilus is called:

Answer: Conjugation

Conjugation requires physical contact between donor and recipient cells via a pilus, through which plasmid DNA is transferred.

A patient has a wound infected with a bacterium that secretes a toxin destroying red blood cells. This toxin is best described as a:

Answer: Hemolysin

Hemolysins are exotoxins that lyse red blood cells, and many are detectable by hemolysis zones on blood agar plates.

Extreme halophiles, thermophiles, and methanogens are all examples of:

Answer: Archaea found in extreme environments

These are all archaea — a domain of prokaryotes distinct from bacteria — that thrive in extreme environmental conditions.