USMLE STEP 1 MICROBIOLOGY QUIZ BANK
EXAM WITH ACTUAL CORRECT QUESTIONS
AND VERIFIED DETAILED ANSWERS|
CURRENTLY TESTING VERSION | ALREADY
GRADED A+|EXPERT VERIFIED FOR
GUARANTEED PASS 2026
What is the flesh-eating bacteria?
Necrotizing fasciitis
Group A Strep
- fast acting
- most likely requiring amputation
- high mortality rate if not diagnosed early
- SpeB toxin
What bacteria can cause cellulitis?
Group A Strep
Staphylococcus aureus
What are the non-suppurative sequelae to Group A Strep infections?
kj: "PHaryngitis can result in rheumatic 'PHever' and glomerulonePHritis"
Rheumatic fever (type II)
Acute Post-Streptococcal infection glomerulonephritis (M12 serotype; type III; "lumpy
bumpy" presentation vs. Goodpasture's syndrome)
kj: "No 'rheum' (room) for SPECCulation"
S: Subcutaneous plaques
1|Page
,P: Polyarthritis
E: Erythema marginatum
C: Carditis
C: Chorea (Sydenham's Chorea)
What's the rapid strep test?
ELISA
25% missed diagnosis
What is the treatment for Streptococcus pyogenes?
1st line:
- β-lactam (penicillin)
- Cases of allergic reaction of penicillin: Macrolides
What is the prevention treatment for Strep. pyogenes?
Prophylactic antibiotics
(For patients at least 5 years post acute rheumatic fever; second onset due to memory
formation against antigen will be very severe)
Macrolides
β-lactams
What are the reservoirs for Group B Strep?
Streptococcus agalactiae
-15~20% in vagina (leading cause for neonatal meningitidis, especially in prolonged
labor)
- Gastrointestinal tract
What are distinguishing markers for Streptococcus agalactiae?
G+
Catalase-
2|Page
,Coagulase-
β-hemolytic
Bacitracin resistant
CAMP sensitive (arrow-head presentation, etc.; identifying β-hemolysis)
What is the treatment for Group B Strep?
Ampicilin + Aminoglycoside/cephalosporin
What is α-hemolytic and diplococcus?
Streptococcus pneumoniae
Streptococcus pneumoniae: Distinguishing features? Transmission? Reservoir?
Features:
- G+ diplococci
- Catalase (-), Coagulase (-)
- α-hemolysis
- Optochin sensitive; quellung formation
- Lysed by bile
- Capsule
Transmission:
- Respiratory droplets
- Often colonized nasopharynx without causing pathology (part of normal flora)
Reservoir:
- Human upper respiratory tract
What are some predisposing factors for S. pneumoniae?
- Antecedent influenza or measles infection ("beat-up" respiratory tract; easier for
infection)
- COPD
3|Page
, - Congestive Heart Failure (CHF)
- Alcoholism
- Asplenia predisposes septicemia (SSHiN; encapsulated bacteria clearance at spleen
function absent in splenectomy)
What are some important pathogenesis factors of S. pneumoniae?
Polysaccharide capsule is the major virulence factor
IgA protease
Teichoic acid
Pneumolysin O: hemolysin/cytolysin
- Inhibits respiratory burst
- Inhibits classical complement fixation
- Damages respiratory tract
What is the most common cause of community acquired pneumonia (CAP) ?
Streptococcus pneumoniae
What are important diseases caused by Streptococcus pneumoniae?
1. Typical pneumonia (CAP)
- Most common cause
- Shaking chills, high fever
- Blood-tinged, rusty sputum
- Lobar consolidation
2. Adult meningitis
- Most common cause
- Teichoic + peptidoglycan are highly toxic in CNS
4|Page
EXAM WITH ACTUAL CORRECT QUESTIONS
AND VERIFIED DETAILED ANSWERS|
CURRENTLY TESTING VERSION | ALREADY
GRADED A+|EXPERT VERIFIED FOR
GUARANTEED PASS 2026
What is the flesh-eating bacteria?
Necrotizing fasciitis
Group A Strep
- fast acting
- most likely requiring amputation
- high mortality rate if not diagnosed early
- SpeB toxin
What bacteria can cause cellulitis?
Group A Strep
Staphylococcus aureus
What are the non-suppurative sequelae to Group A Strep infections?
kj: "PHaryngitis can result in rheumatic 'PHever' and glomerulonePHritis"
Rheumatic fever (type II)
Acute Post-Streptococcal infection glomerulonephritis (M12 serotype; type III; "lumpy
bumpy" presentation vs. Goodpasture's syndrome)
kj: "No 'rheum' (room) for SPECCulation"
S: Subcutaneous plaques
1|Page
,P: Polyarthritis
E: Erythema marginatum
C: Carditis
C: Chorea (Sydenham's Chorea)
What's the rapid strep test?
ELISA
25% missed diagnosis
What is the treatment for Streptococcus pyogenes?
1st line:
- β-lactam (penicillin)
- Cases of allergic reaction of penicillin: Macrolides
What is the prevention treatment for Strep. pyogenes?
Prophylactic antibiotics
(For patients at least 5 years post acute rheumatic fever; second onset due to memory
formation against antigen will be very severe)
Macrolides
β-lactams
What are the reservoirs for Group B Strep?
Streptococcus agalactiae
-15~20% in vagina (leading cause for neonatal meningitidis, especially in prolonged
labor)
- Gastrointestinal tract
What are distinguishing markers for Streptococcus agalactiae?
G+
Catalase-
2|Page
,Coagulase-
β-hemolytic
Bacitracin resistant
CAMP sensitive (arrow-head presentation, etc.; identifying β-hemolysis)
What is the treatment for Group B Strep?
Ampicilin + Aminoglycoside/cephalosporin
What is α-hemolytic and diplococcus?
Streptococcus pneumoniae
Streptococcus pneumoniae: Distinguishing features? Transmission? Reservoir?
Features:
- G+ diplococci
- Catalase (-), Coagulase (-)
- α-hemolysis
- Optochin sensitive; quellung formation
- Lysed by bile
- Capsule
Transmission:
- Respiratory droplets
- Often colonized nasopharynx without causing pathology (part of normal flora)
Reservoir:
- Human upper respiratory tract
What are some predisposing factors for S. pneumoniae?
- Antecedent influenza or measles infection ("beat-up" respiratory tract; easier for
infection)
- COPD
3|Page
, - Congestive Heart Failure (CHF)
- Alcoholism
- Asplenia predisposes septicemia (SSHiN; encapsulated bacteria clearance at spleen
function absent in splenectomy)
What are some important pathogenesis factors of S. pneumoniae?
Polysaccharide capsule is the major virulence factor
IgA protease
Teichoic acid
Pneumolysin O: hemolysin/cytolysin
- Inhibits respiratory burst
- Inhibits classical complement fixation
- Damages respiratory tract
What is the most common cause of community acquired pneumonia (CAP) ?
Streptococcus pneumoniae
What are important diseases caused by Streptococcus pneumoniae?
1. Typical pneumonia (CAP)
- Most common cause
- Shaking chills, high fever
- Blood-tinged, rusty sputum
- Lobar consolidation
2. Adult meningitis
- Most common cause
- Teichoic + peptidoglycan are highly toxic in CNS
4|Page
