B4.068 - Staph Aureus a Pyogenic Model Flashcards
common gram negative pus forming bacteria
Neisseria E. Coli Pseudomonas
common gram positive pus forming bacteria
Strep pyogens staph aureus
what is suppuration
the formation of pus
what is pus
a mixture of living and dead neutrophils, bacteria and cellular debris
where does pus usually form
in an area of persistent infection
what is an abcess
a circumscribed collection of pus associated with infection
does an abscess respond to antibodies or antibiotics
no, not accessible
one way to get rid of abscesses
drain it
how do abscesses form
activation of macrophages and other cells of the innate immune system chemotactic factors produced by resident cells - acute phase response activation of adaptive immunity and Th17 acute inflammation
what cells are involved in acute inflammation
infiltration of neutrophils production of lysosomal enzymes
describe how the shape of an abscess forms
the inflammatory area is contained within a thick walled fibrin capsule the host thinks it has contained an invading organism
what is a complication of abscesses
if the abscess happens to be in or near a vital organ or tissue it can often have serious consequences
describe staph a.
gram + coccus grows in irregular grape like clusters non motile, non spore forming and catalase and coagulase positive
what is staph a resistant to
high temp high salt (haloduric) drying
describe how staph a looks
colonies are golden and strongly beta hemolytic on blood agar
describe staph a on mannitol salt agar
produces a yellow color with phenol red indicator
what is ClfB
clumping factor B
what is IsdA
iron regulated surface determinant
what populations have higher rates of staph colonization
health care workiers diabetics patients on dialysis
main site of staph a colonization
anterior nares
other staph a colonization sites
axilla, rectum, perineum vaginal carriage rate is 10% in premenopausal women, rate higher during menses
how can staph spread inside the body
from abscesses heatogenously
how does staph. a spread hematogenously
due to proteolytic enzymes
can result in pneumonia, bone and joint infection and heart valve infection
janeway lesions seen in endocarditis
osler nodes seen in endocarditis
roth spots seen in endocarditis
how does endocarditis initially present
fever and malaise
mortality rate of staph a septicemia
80%
mortality rate of staph a TSS
3-5%
TSS criteria for diagnosis
Fever > 38.9
Rash
hypotension
nausea, vomiting, diarrhea
myalgia, high Cr
conjuctival hyperemia
blood urea high
high bilirubin, transaminases
thrombocytopenia
disorentation
what is a concern for a neutropenic cancer patietn with a central venous line
sepsis due to s. aureus
most frequent cause of septicemia following a surgical procedure
staph aureas
most common place to contract MRSA
hospital
common manifestations of staph
skin
wound
scalded skin syndrome
common staph skin infections
folliculitis
furuncles, carbuncles
impetigo
what is ritter disease
scalded skin syndrome
folliculitis
a tender pustule involving a hair follicle
furuncle
small abscess that exudes purulent material from a single opening
carbuncle
an aggregate of furuncles with several openings
typical findings of septic arthritis
warmth
erythema
tenderness of the joint with symptoms and fever
infection almost always unilateral
what is osteomyelitis
bone infection indicated by fever and bony tenderness or limp
catheter associated infections are often due to what
staph epidermis
urinary tract infections in sexually active young firls often due to
staph saprophyticus
staph saprophyticus symptoms
often seen in sexually active young girls
dysuria
pyuria
does staph aureus have a capsule
yes, inhibits phagocytosis
what is protein A
seen in staph a
binds to the H chain of antibody and can inhibit antibody opsonization preventing phagocytosis. can activate the classical C pathway
is s. aureus coagulase + or -
positive
this means it was the ability to coagulate plasma and form a fibrin barrier around infectious loci.
what is staphylokinase
something staph aureus can relase that breaks down fibrin clots, note it is also coagulase + so it has the ability to make clots and break them down
what is PVL
panton valentine leukocidin
a phage derived exotoxin that causes leukocyte destruction and necrosis. espeicially in the skin and lungs
what are exfoliatin toxins
seen in staph aureus
consists of ETA or ETB
result in scalded skin syndrome
features of scalded skin syndrome
fever
erythema
blisters (bullae) which eventually rupture adn leave a red base.
positive nikoskys signs
what is bullous impetigo
a localized form of SSSS
unlike disseminated SSSS the bulae are culture positive
nikoskys sign absent
occurs primarily in infants and young children
highly communicable
what are enterotoxins A-E adn G-I
responsible for types of common food poisoning
staph aureus
supeantigens that stimulate ceratin T cells by binding to the TCR Vbeta chain
stimulate production of cytokines like IFN gamma and TNF causing inflammation of the tissues
antigen on left
superantigen on right
what are enterotoxins and what do they do
often localized to the gut but can be fatal if systemic
often occur from skin of food handlers
cause vomiting and watery diarrhea 2-6 hours after ingestion
symptoms usually self limited
should you give antibiotics for enterotoxin mediated staph food poisoning
no it wont help, the toxin is there its not the bug causing the problem. its self limited
what is TSS
caused by a superantigen
first described in children
frequently associated with tampons
associated with strains that produced TSST-1
mimics endotoxic shock
what strains other than ones that produce TSST-1 can cause toxic shock
ones that produce enterotoxin B, C can cause 50% of cases of non mestrual TSS
pathophys mimics endotoxic shock
case definition of TSS
fever
diffuse macular erythema
may mimic sunburn rash
hypotension
involvement of organ systems
GI - emesis or diarrhea
renal dysfunction
hematologic - low platelets
muscular - severe myalgia
hepatic - elevated liver enzymes
NS - diorientation
diagnosis fo staph aureus
culturs with susceptibility testing
blood culture may be positive when results from other cultures are negative
most purulent infections caused by what
staph aureus unless proven otherwise
most important defense agaistn s. aureus
neutrophils
what are important immunological factors for defense against staph aureus
opsonization and antibody and Cā involved
what is not a major factor in staph aureus defense
MAC
what adaptive components of the immune system are importatn in staph aureus defense
T cells - Th17
IL-1
what is the most important innate immune system componet for staph aureus
TLR-2 - peptidoglycan
women who experiecen TSS have what
lower antibody titers againts TSST-1
coagulase negative staph types
staph epidermidis most common
lack many virulence factors and often require a means of entry
staph epidermidis can cause problems with what
artifical heart valves, strep more common for natural valves
also catheters
what indicates a positive coagulase test
formation of fibrin clot or gel
why does staph enterotoxin B cause observed clinical effects
it activates certain T cells to produce cytokines
staph superantigens stimulate what
T cells
endotoxins stimulate what part of the immune system
macrophages
left - spider bite
right - MRSA
differentiate using a culture
