general features of staph aureus
G(+) clusters
catalase (+)
coagulase (+)
where do you normally find s. aureus
ubiquitous - skin + membranes
how does s. aureus normally cause infection?
- breaks in skin: wound infections
- secondary overgrowth: sinusitis, OM
- get into blood stream: only problem for immunocompromised -> heart, joints, bones
- most common cause of acute endocarditis, joint infections, osteomyelitis
what can s. aureus cause in very immunocompromised patients?
necrotizing pneumonias
what are s. aureus infections characterized by, histologically?
neutrophils!
- supporative: localized collections of pus -> abscesses
- liquefactive necrosis
- role of phagocytosis/opsonization very important
what is the role of protein A in s. aureus?
it binds Ab’s backwards (on the Fc portion), blocking opsonization
problems S. aureus can cause
- supporative disease - impetigo, folliculitis
- enteritis
- TSS
- post-op pneumonia
- Staph scalded skin syndrome (SSSS)
- food poisoning (enterotoxin)
staph virulence factors
- coag (+) in aureus
- enterotoxins
- cytolytic toxins
- exfoliative toxins
- TSST-1
- lipases
- penicillinase
- fibronectin and vitronectin (bind to host cells)
- protein A
types of staph infections
- overgrowth of normal flora/ URT:
- sinusitis
- OM
- access to sterile areas:
- skin/wound infections
- hematogenous spread from punctures
- bacteremic spread to joints, bone, heart valves, etc.
- ingestion/absorption of toxins
- deep infections in immunocompromised/debilitated
- necrotizing pneumonia
- septicemia
types of staph skin/wound infections
- furuncle
- carbuncle (many furuncles communicating under skin)
- associated with suture/ foreign bodies
- surgical wounds
- impetigo (horny layers of skin)
- major cause of infection in burns and surgical wounds**
- common cause of nosocomial infections**
incubation of staph enterotoxin
1-6 h
what food is staph food poisoning associated with?
- custards
- milk products
- meats
- potato salad
describe staph TSS
- from T cell super Ag (non-specific activation)
- fever, vasodilation - diffuse macular rash, shock, hypotension
- confused with G(-) sepsis
describe staph bacteremia
- relatively common, but non-threatening
- seeding of damaged tissues from circulation
- acute endocarditis
- septic arthritis
- osteomyelitis
- meningitis
describe staph bronchopneumonia
- in debilitated patients (nosocomial)
- secondary to viral infection or obstructive illness
- very destructive purulent lesions**
Staph saprophyticus
- present in the normal skin, periurethral, and urethral flora
- cause UTIs in young women
- most asymptomatic
coagulase (-)
staph epidermidis
- coagulase (-)
- only infects inert objects (catheters, artificial tissues, prosthetics, etc.)
difference between CA-MRSA and HA-MRSA
CA: susceptible to everything besides methicillin
HA: only susceptible to vancomycin
what does MRSA often present as?
clusters of abscesses or ‘spider bites’
