Part 1: Staph Flashcards
(30 cards)
The three major classes of gram-positive cocci:
- Staphylococcus
- Streptococcus
- Enterococcus
General characteristics of staphylococci:
- gram-positive cocci; grape clusters.
- facultative anaerobes.
- catalase positive.
- hardy: resistant to heat and drying.
How to differentiate between staphylococci and streptococci:
- catalase status:
- staph: catalase positive.
- strep: catalase negative.
What is catalase?
enzyme that converts H2O2 to H2O and oxygen.
The 3 major classes of staphylococci:
- S. aureus
- S. epidermidis
- S. saprophyticus
S. aureus diagnostics/identification (4):
- gram-positive cocci clusters (grapes).
- golden-yellow colonies (beta-hemolytic).
- catalase positive.
- coagulase positive.
How to differentiate S. aureus from S. epidermidis and S. saprophyticus:
-
S. aureus is coagulase positive.
- S. epidermidis and S. saprophyticus are coagulase negative.
Where does S. aureus normally colonize humans?
anterior nares.
What virulence factors are located on the cell envelope of S. aureus (3)?
CAP
- capsule (antiphagocytic)
- adhesins (attachment)
- protein A (binds IgG Fc)
What exotoxins are secreted by S. aureus (5)?
HPEET
- hemolysin (lyse RBCs).
- panton-valentine leukocidin (lyse PMNs).
- enterotoxins (food poisoning).
- exfoliatin (scalded skin syndrome).
- toxic shock syndrome toxin (TSST-1).
What are the superantigen exotoxins secreted by S. aureus (3)?
- enterotoxins (food poisoning).
- exfoliatin (scalded skin syndrome).
- toxic shock syndrome toxin (TSST-1).
What do superantigens do?
- non-specifically crosslink MHC2 to TCR; activates T lymphocytes.
- cytokine storm results.
What invasins are secreted by S. aureus that allow it to penetrate tissue (3)?
- Staphylokinase
- Hyaluronidase
- Lipase
Why is S. aureus a very common hospital infection?
hardy bacteria; persists on fomites.
Most common clinical presentation of S. aureus infection:
skin and soft tissue infections (SSTIs).
The 4 types of skin and soft tissue infections (SSTIs) caused by S. aureus:
FICC
- furuncles (small abcess)
- impetigo (crusted skin infection)
- carbuncles (large skin abcess)
- cellulitis (deep skin infection)
The 5 types of deep tissue infections caused by S. Aureus:
BSOAP
- bloodstream infections
- septic joint
- osteomyelitis
- acute endocarditis
- pneumonia
Symptoms of toxic shock syndrome:
high fever, sun-burn like rash, multi-organ failure.
What causes S. Aureus resistance to penicillin?
beta-lactamase (penicillinase).
What causes S. Aureus resistance to methicillin?
altered penicillin-binding protein 2a.
MRSA is resistant to all drugs of which class?
All beta-lactam antibiotics.
Standard of care antibiotic for MRSA:
vancomycin.
S. epidermidis diagnostics/identification (4):
- gram-positive cocci clusters (grapes).
- catalase positive.
- coagulase negative.
- novobiocin sensitive.
S. saprophyticus diagnostics/identification (4):
- gram-positive cocci clusters (grapes).
- catalase positive.
- coagulase negative.
- novobiocin resistant.
