Staphylococcus Aureus Flashcards
coagulase positive or negative
positive
coagulase
the ability to clot
pigment on agar
gold
alpha, beta, or gamma hemolytic
beta hemolytic
ferments….
manitol
what type of media is mannitol-salt agar
selective and differential
catalase positive or negative
positive
catalase
breaks down H2O2 produced during oxidative metabolism
beta lactamase positive or negative?
positive
beta lactamase
resistant to penicillins and cephalosporins
epidemiology
very contagious
reservoir
humans are nasal carriers
- may also colonize skin and mucous membranes
transmission
direct skin to skin contact
indirect contact via fomites
ingestion of contaminated
major virulence factors
capsule
catalase
exotoxins
coagulase
staphylolusin
leukocidin
protein A
hyaluronidase
catalase
neutralizes hydrogen peroxide
- counteracts phagocyte’s oxidative killing
capsule
composed of polysaccharides
- inhibit phagocytosis
staphylolysin
lysis red blood and white blood cells
enterotoxin
potent gastrointestinal toxin as well as super antigen activity
toxic shock syndrome toxin 1
act as a potent super antigen
exfoliative toxin
an exotoxin that causes desquamation of the skin, weak superantigen activity
protein A function
inhibits functions of antibodies
- does not allow binding to the virus
hyaluronidase
degrades hyaluronic acid that cements cells together to promote spreading through tissues
disease
skin diseases (including abscesses)
toxin-mediated :
- staphylococcal food poisoning
- scalded skin syndrome
- toxic shock syndrome
infection
colonization
intoxication
toxin production (outside of host)
infection and intoxication
colonization and then toxin production (inside of host)
pyogenic
pus producing
pyogenic infections are characterized by the formation of an
abscess
pathogenesis of S. aureus skin infections
enters through tiny break or opening in skin
replicates and releases virulence factors that damage tissue and body responds
inflammation (PMNs arrive and phagocytize bacteria and dead cells)
cavity forms filled with pus
cavity expands
local fibroblasts lay down fibrin around pus filled cavity
antibiotics alone can’t penetrate the abscess so it requires drainage
folliculitis
infection of hair follicle
- resolves or progresses to furuncle
furuncle
boil, large painful lesion that extends from hair follicle to surrounding tissues
- resolves or progresses to carbuncle
carbuncle
multiple interconnected abscesses forming from the aggregation of furuncle
- requires debridement nad antibiotics
impetigo
small flattened red patches -> pus filled vesicles -> rupture and crust over
- common among infants and young children
- itchy, highly contagious
food poisoning
when it is caused by a toxin not an infection it is food poisoning
- symptoms: nausea and vomiting (NO FEVER)
staph food poisoning is an example of
intoxication
staphylococcal enterotoxin
can cause food intonation
- resistant to low pH
- heat stable
- superantigen activity
why do you think blood cultures failed to isolate any pathogens
there were no bacteria in the blood samples because replicating bacteria were not causing the systemic disease
toxic shock syndrome is an example of
infection and intoxication
toxic shock syndrome
caused by toxic shock syndrome toxin 1
- incudes fever, vomiting, rash, and shock
- act as a potent super antigen
- causes 75% of all cases
symptoms of toxic shock
abrupt onset of high fever
red erythematous (sunburn-like) rash
desquamation
hypotension -> multi system organ failure
staphylococcal scalded skin syndrome (SSSS)
localized infection, systemic intoxication
- causes by exfoliative toxin (causes desquamation)
- weaker than TSS-1
symtoms of SSSS
erythema (redness) followed by desquamation
no scarring
typically affects neonates and infants
potential complication
potential complication of SSSS
a secondary infection of areas where the skin has peeled away
management of staphylococcal infections
boils, carbuncles may require minor surgery to drain pus
antibiotic treatment often follows debridement
staylococci produce
penicillinase ( a type of beta lactamase)
methicillin resistant S. aureus (MRSA)
these strains are resistant to beta lactic antibiotic, being sensitive only to vancomycin
-associated with worse outcomes such as longer hospital and ICU stays and higher mortality rates
