Bacteria Flashcards
5 Morphologic characteristics of Staphylococcus aureus
Gram-positive cocci
Catalase+
Coagulase+
Beta-hemolytic
Mannitol fermenter (turns salt agar yellow)
Main virulence factor associated with Staph aureus — component of cell wall which binds Fc region of Abs and prevents complement activation thus preventing opsonization and phagocytosis
Protein A
What area of the body does Staph aureus tend to colonize?
Nares (nose)
What are the 5 inflammatory diseases caused by Staph Aureus?
- Post-viral bacterial pneumonia (patchy infiltrate on CXR)
- Septic arthritis (#1 cause)
- Large erythematous abscesses
- Rapid onset bacterial endocarditis (IV drug use, often tricuspid valve)
- Osteomyelitis in adults (#1 cause)

3 morphologic features of Staphylococcus epidermidis and saprophyticus
Gram+
Catalase+
Urease+
Coagulase -
What morphologic feature differentiates Staphylococcus aureus from Staph epidermidis and saprophyticus?
Staph aureus is coagulase+
Epidermidis and saprophyticus are coagulase -
What organism is a part of normal skin flora and tends to infect hardware, orthopedic joints, heart implants, catheters, etc.?
What virulence factor contributes to its ability to do this?
- Staphylococcus epidermidis
- Polysaccharide capsule: ability to form biofilms to stick to metal and plastic surfaces
What organism is associated with contamination of blood cultures?
Staph epidermidis
What is the major clinical manifestation of staphylococcus saprophyticus?
UTI’s in sexually active females (2nd most common cause to E.coli) “Honeymoon cystitis”
Morphologic features of streptococcus pyogenes (group A strep)
Gram+ cocci in chains
Microaerophilic
Hyaluronic acid capsule
Beta-hemolytic
5 Virulence factors associated with S. pyogenes (Group A strep)
M-protein (anti-phagocytic, humoral response - Abs to heart)
Streptococcal pyrogenic exotoxin
Streptolysin O
Streptokinase
DNA-ase
Clinical manifestations of strep pyogenes infection (note which ones are toxin-mediated vs. M-protein mediated)
Pyogenic infections:
Impetigo, strep throat, erysipelas, cellulitis
Toxin-mediated:
Scarlet fever, TSLS, Necrotizing fasciitis
M protein-mediated:
Rheumatic fever = polyarthritis, endocarditis (mitral valve), nodules on extensor surfaces, erythema marginatum, sydenham’s chorea [JONES]
Post-streptococcal glomerulonephritis:
Facial edema, hematuria (“cola” colored urine), HTN
How would you test for a group A strep infection?
ASO antibody titer
3 symptoms of Scarlet fever?
Caused by what toxin?
- Strawberry tongue
- Pharyngitis
- Widespread rash that spares the face
- Caused by streptococcal pyrogenic exotoxin (SPE)
Which superantigens mediate TSLS vs. Necrotizing fasciitis in strep pyogenes infections?
- TSLS = SpeA, SpeC
- Nec Fasc = SpeB
Post-streptococcal glomerulonephritis tends to occur after what type of strep pyogenes infection(s)?
Either pharyngitis OR superficial infection like impetigo
Rheumatic fever tends to occur after what type of strep pyogenes infection(s)?
Pharyngitis only (NOT impetigo!)
What organism tends to cause serious infections in newborns, thus pregnant mothers should be swabbed at ~35 weeks?
Streptococcus agalactiae (group B strep)
Morphologic features of strep agalactiae and distinguishing tests?
Gram+ cocci in chains
Facultative anaerobe
Beta-hemolytic
Polysaccharide capsule
cAMP test + (increasing zone of hemolysis when plated w/ S. aureus)
Hippurate test +
Clinical manifestations of streptococcus agalactiae (Group B strep)
- Neonatal meningitis (no nuchal rigidity!) = #1 cause
- Strep throat (pharyngitis)
- Pneumonia
Morphologic features of streptococcus pneumoniae?
Gram + diplococci
Polysaccharide capsule = major VF
Alpha-hemolytic
Facultative anaerobe
Optochin-sensitive
Bile-soluble
Characteristic feature of otitis media caused by streptococcus pneumoniae
Bullous meringitis
Major virulence factors of strep pneumoniae?
- Polysaccharide capsule
- IgA protease = allows colonization and invasion of mucosa!
Diagnosis of strep pneumoniae involves the ____ reaction, which turns blue in the presence of strep pneumo
Quelling






































