MCPHS MICROBIOLOGY SELF
PACED EXAM 2025 QUESTIONS
AND ANSWERS
Pathogenicity - ....ANSWER ...-The ability to cause disease
Virulence - ....ANSWER ...-the extent of pathogenicity
Portals of entry - ....ANSWER ...-mucous membranes, skin, parenteral route
ID50 (infectious dose) - ....ANSWER ...-The number of microbes that must
enter the body to establish infection in 50% of test animals is expressed as the
ID50
LD50 - ....ANSWER ...-lethal dose (of a toxin) for 50% of the test
population
Adherence - ....ANSWER ...-Adhesions / ligands bind to receptors on host
cells, form biofims
Glycocalyx: streptococcus mutans
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,Fimbriae: E.coli
M proteins: Strepoccus pyogenes
Pili, flagella, glycoproteins, lipoproteins
Capsules - resist phagocytosis - ....ANSWER ...-Strep. Pneumoniae, Hib,
bacillus anthracis
cell wall components - ....ANSWER ...-M proteins: mediates attachment and
resists phagocytosis (strep. pyogenes)
Opa protein: assist attachment and recept mediated endocytosis, inhibs helper t
cells (n. gonorrhoeae)
Mycolic acid: Waxy, resists digestion (mycobacterium TB)
Enzymes - ....ANSWER ...-Coagulase: coagulates fibrinogen
Kinases: digest fibrin clots
hyaluronidase: hydrolyzes hyaluronic acid
Collagenase: hydrolyzes collagen
IgA proteases: destroys IgA antibodies
antigenic variation - ....ANSWER ...-Alteration of surface antigens to avoid
detection by host antibodies
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 2
,Examples: flu, gonorrhea, trypanosoma brucei gambiense
Invasins: Penetration into the host cell cytoskeleton - ....ANSWER ...-
Salmonella alters host actin to enter a host cell
Listeria uses actin to move from one cell to the next
Direct damage caused by - ....ANSWER ...-disrupting the host cells function
produces waste products
toxins
induce hypersensitive reactions
damage immediate vicinity
use hosts nutrients (iron) -siderophores
Siderophores - ....ANSWER ...-proteins that free host stores of iron
Toxin - ....ANSWER ...-substance that contributes to pathogenicity
Toxoid - ....ANSWER ...-inactivated toxin used in a vaccine
Antitoxin - ....ANSWER ...-antibodies against a specific toxin
Endotoxins - ....ANSWER ...-the lipid portions of lipopolysaccharides (LPS)
that are part of the outer membrane of the cell wall of gram-negative bacteria. The
endotoxins are liberated when the bacteria die and the cell wall breaks apart.
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 3
, PART OF BACTERIAL CELL NOT A PRODUCT
Lipid NOT proteins
all produce same SS
Exotoxins - ....ANSWER ...-specific for a structure or function in host cell
Can be gram pos or neg
Are proteins, enzymes
secreted into medium during log phase
most lethal
produce SS
Classification of exotoxins - ....ANSWER ...-1. Based on host cell attacked
(cardiotoxin)
2. Disease they are associated with: tetanus
3. Bacterium that produces it: botulinum
4. Structure/function: A-B, Membrane-disrupting, superantigens
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 4
PACED EXAM 2025 QUESTIONS
AND ANSWERS
Pathogenicity - ....ANSWER ...-The ability to cause disease
Virulence - ....ANSWER ...-the extent of pathogenicity
Portals of entry - ....ANSWER ...-mucous membranes, skin, parenteral route
ID50 (infectious dose) - ....ANSWER ...-The number of microbes that must
enter the body to establish infection in 50% of test animals is expressed as the
ID50
LD50 - ....ANSWER ...-lethal dose (of a toxin) for 50% of the test
population
Adherence - ....ANSWER ...-Adhesions / ligands bind to receptors on host
cells, form biofims
Glycocalyx: streptococcus mutans
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 1
,Fimbriae: E.coli
M proteins: Strepoccus pyogenes
Pili, flagella, glycoproteins, lipoproteins
Capsules - resist phagocytosis - ....ANSWER ...-Strep. Pneumoniae, Hib,
bacillus anthracis
cell wall components - ....ANSWER ...-M proteins: mediates attachment and
resists phagocytosis (strep. pyogenes)
Opa protein: assist attachment and recept mediated endocytosis, inhibs helper t
cells (n. gonorrhoeae)
Mycolic acid: Waxy, resists digestion (mycobacterium TB)
Enzymes - ....ANSWER ...-Coagulase: coagulates fibrinogen
Kinases: digest fibrin clots
hyaluronidase: hydrolyzes hyaluronic acid
Collagenase: hydrolyzes collagen
IgA proteases: destroys IgA antibodies
antigenic variation - ....ANSWER ...-Alteration of surface antigens to avoid
detection by host antibodies
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 2
,Examples: flu, gonorrhea, trypanosoma brucei gambiense
Invasins: Penetration into the host cell cytoskeleton - ....ANSWER ...-
Salmonella alters host actin to enter a host cell
Listeria uses actin to move from one cell to the next
Direct damage caused by - ....ANSWER ...-disrupting the host cells function
produces waste products
toxins
induce hypersensitive reactions
damage immediate vicinity
use hosts nutrients (iron) -siderophores
Siderophores - ....ANSWER ...-proteins that free host stores of iron
Toxin - ....ANSWER ...-substance that contributes to pathogenicity
Toxoid - ....ANSWER ...-inactivated toxin used in a vaccine
Antitoxin - ....ANSWER ...-antibodies against a specific toxin
Endotoxins - ....ANSWER ...-the lipid portions of lipopolysaccharides (LPS)
that are part of the outer membrane of the cell wall of gram-negative bacteria. The
endotoxins are liberated when the bacteria die and the cell wall breaks apart.
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 3
, PART OF BACTERIAL CELL NOT A PRODUCT
Lipid NOT proteins
all produce same SS
Exotoxins - ....ANSWER ...-specific for a structure or function in host cell
Can be gram pos or neg
Are proteins, enzymes
secreted into medium during log phase
most lethal
produce SS
Classification of exotoxins - ....ANSWER ...-1. Based on host cell attacked
(cardiotoxin)
2. Disease they are associated with: tetanus
3. Bacterium that produces it: botulinum
4. Structure/function: A-B, Membrane-disrupting, superantigens
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 4
