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Microbiology Usmle step 1 Exam questions with correct solutions
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Microbiology Usmle step 1 Exam
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Microbiology Usmle step 1Gram-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 - answerClassification:
-- Anaerobic gram-positive cocci
Characteristic:
-- A normal flora of the mouth and colon.
-- This organism forms abscesses in patients with alcoholism and seizure disorder
Fusobacterium species - answerClassification:
-- Anaerobic gram-negative rods microorganism
Characteristic:
-- It forms abscesses in patients with alcoholism and seizure disorder. They are part of
the human normal flora of the mouth, colon, and female genital tract.
Staph. epidermidis - answerClassification:
-- Gram-Positive Cocci, Novobiocin sensitive.
-- Catalase positive, Coagulase-negative
Characteristic:
-- This organism infects prosthetic devices and intravenous catheters by producing
adherent biofilms. A compound of normal skin and nose flora.
,Staph. saprophyticus - answerClassification:
-- Gram-Positive Cocci, Novobiocin resistant
-- Catalase positive, Coagulase-negative
Characteristic:
-- The Second most common cause of uncomplicated UTI in young women.
Strep. pneumoniae - answerClassification:
-- A lancet-shaped encapsulated gram-positive diplococci. (Alpha hemolytic)
-- Optochin sensitive, Catalase negative.
Characteristic:
-- It causes symptoms of meningitis, otitis media (in children), pneumonia, sinusitis, and
rusty color sputum.
-- Also, secrete IgA protease
Viridans streptococci - answerClassification:
-- Gram-Positive Cocci (alpha hemolytic)
- Optochin resistant, Catalase negative.
Characteristic:
-- It is a normal flora of the oropharynx
that affects dental caries (S. Mutans) and causes subacute bacterial endocarditis at
damaged valves (S.sanguinis).
Strep. pyogenes - answerClassification:
-- Gram-Positive Cocci (beta-hemolytic)
-- Bacitracin sensitive, catalase negative
Characteristic:
-- Secretes M protein to protect itself from phagocytosis.
-- It may present with pharyngitis, cellulitis, necrotizing fasciitis, and acute
glomerulonephritis.
Strep. agalactiae (B group) - answerClassification:
-- Gram-Positive Cocci (beta-hemolytic)
--Bacitracin resistant, catalase negative.
, Characteristic:
-- It causes pneumonia, meningitis, and sepsis in babies.
Strep. bovis - answerClassification:
-- Gamma hemolytic microorganism
-- Gram-Positive Cocci that colonized the gut.
Characteristic:
-- It also causes subacute endocarditis in colon cancer patients.
Straph. aureus - answerClassification:
-- Gram-Positive Cocci
-- Catalase positive and coagulase positive organism.
Characteristic:
-- This organism is responsible for bringing toxic shock syndrome, scalded skin
syndrome (exfoliative toxin), food poisoning, and acute endocarditis (IV drug users), and
hepatic abscess.
Enterococcus faecalis, faecium (Streptococci) - answerClassification:
-- Gram-Positive Cocci
Characteristic:
-- Group D streptococci that cause endocarditis after genitourinary procedures.
Corynebacterium diphtheriae - answerClassification:
-- Gram-Positive Rod or Bacilli
-- Inactivate elongation factor (EF-2)
Characteristic:
-- Symptoms are pseudomembranous pharyngitis and severe cervical lymphadenopathy
(bull neck).
Clostridium tetani - answerClassification:
-- Gram-Positive Rod or Bacilli
Characteristic:
-- This organism secretes toxins that cleave SNARE protein and prevents the release of
inhibitory neurotransmitters in the Renshaw cell (inside the spinal cord).
-- Symptoms are spasticity and lockjaw.
Clostridium botulinum - answerClassification:
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