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Microbiology USMLE Step 1 D Exam with solutions
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Microbiology USMLE Step 1 D Exam
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Microbiology USMLE Step 1Staph. epidermidis - answerNovobiocin sensitive, Catalase positive, Coagulase
negative, Infects prosthetic devices and intravenous catheters by producing adherent
biofilms. Compound of normal skin flora. (Gram-Positive Cocci)
Gram-positive organisms - answer____ have a thick peptidoglycan layer and teichoic
acid in their cell walls
Gram-negative organisms - answer____ have a thin peptidoglycan layer and a complex
outer membrane containing lipopolysaccharide (LPS).
Lipoteichoic acid - answer____ is a teichoic acid attached to a lipid abundant on Gram-
positive bacteria cell wall.
Peptostreptococci - answer____ are anaerobic gram-positive cocci found as members
of the normal flora of the mouth and colon. They are also isolated from abscesses of
various organs, usually from mixed anaerobic infections.
Fusobacterium species - answer____ are anaerobic gram-negative rods with pointed
ends. They are part of the human normal flora of the mouth, colon, and female genital
tract
Staph. saprophyticus - answerNovobiocin resistant, Catalase positive, Coagulase
negative, second most common cause of uncomplicated UTI in young women. (Gram-
Positive Cocci)
Strep. pneumoniae - answerAn alpha hemolytic bacteria that is a catalase negative and
optochin sensitive. A lancet-shaped encapsulated gram-positive diplococci that secretes
IgA protease. It cause symptoms of meningitis, otitis media (in children), pneumonia,
sinusitis, and rusty color sputum. (Gram-Positive Cocci)
Viridans streptococci - answerAn alpha hemolytic bacteria that is a catalase negative
and optochin resistant. It is a normal flora of the oropharynx that affects dental caries
(S. Mutans) and causes subacute bacterial endocarditis at damaged valve
(S.sanguinis). (Gram-Positive Cocci)
, Strep. pyogenes - answerA bacitracin sensitive microorganism that secretes M protein
to protect itself from phagocytosis. It is the leading bacterial cause of pharyngitis and
cellulitis. It may present as necrotizing fasciitis and acute glomerulonephritis. (Gram-
Positive Cocci)
Strep. agalactiae (B group) - answerA bacitracin resistant microorganism that belongs
to the Beta-hemolytic group. It causes pneumonia, meningitis, and sepsis in babies.
(Gram-Positive Cocci)
Strep. bovis - answerA gamma hemolytic bacteria that colonized in the gut. It also
causes subacute endocarditis in colon cancer patients. (Gram-Positive Cocci)
Straph. aureus - answerThis bacteria is responsible for bringing toxic shock syndrome,
scalded skin syndrome (exfoliative toxin), food poisoning, and acute endocarditis (IV
drug users). (Gram-Positive Cocci)
Corynebacterium. diphtheriae - answerInactivate elongation factor (EF-2). Present with
symptoms of pharyngitis with pseudomembranes in throat and severe
lymphadenopathy. (Gram-Positive Rod or Bacilli)
Clostridium tetani - answerThis bacteria secreted toxins that cleaves SNARE protein
and prevents the release of inhibitory (GABA and glycine) neurotransmitters from
Renchaw cell in spinal cord. Symptoms are spasticity and lockjaw. (Gram-Positive Rod
or Bacilli)
Clostridium botulinum - answerThis bacteria secreted toxins that cleaves SNARE
protein and prevents the release of stimulatory (ACh) neurotransmitters. Symptoms are
flaccid paralysis (floppy baby). (Gram-Positive Rod or Bacilli)
Clostridium perfringens - answerWhat bacteria produces phospholipase (lecithinase)
that degrades tissue and cell membranes which forms gas gangrene. It also secretes
Alpha toxins and create double zone hemolysis on blood agar. (Gram-Positive Rod or
Bacilli)
Clostridium difficile - answerThis bacteria is known to produce toxin A (enterotoxin) and
toxin B (cytotoxin) which resulted into pseudomembranous colitis. (Gram-Positive Rod
or Bacilli)
Bacillus anthracis - answerSecrete a toxin called edema factor which mimics the
adenylate cyclase enzyme (cAMP). Present with symptoms of edematous border of
black eschar in the cutaneous. It causes Wool sorter's disease (life threatening
pneumonia). (Gram-Positive Rod or Bacilli)
Bacillus cereus - answerA bacteria that causes food poisoning by forming spores that
can survive in heated or reheated rice. Symptoms are nausea and vomiting within 1 to 5
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