AP-Micro Microbiology: Microbial Ecology and Pathogenesis 3

Question 1

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

Accepted Answer

M protein

Answer

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

Question 2

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

Accepted Answer

Sulfate reduction

Answer

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

Question 3

Quorum sensing in bacteria refers to:

Accepted Answer

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

Answer

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

Question 4

Which of the following best defines 'pathogenicity'?

Accepted Answer

The ability of a microorganism to cause disease in a host

Answer

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

Question 5

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

Accepted Answer

Conjugation

Answer

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

AP Practice Test

AP Practice Test

AP-Micro Microbiology: Microbial Ecology and Pathogenesis 3