Staph Flashcards
what shape is Staphylococcus?
cocci, like a bunch of grapes
what oxygen levels does Staph require?
facultative anaerobe
how does Staph metabolise?
fermentation AND respiration
what does Staph produce as a result of metabolism?
lactic acid
how to distinguish Staph from Strep?
Staph= catalase POSITIVE
what is the GC content of Staph?
30-40 (low)
is S.aureus coagulase positive/negative? what is this used to distinguish from?
POSITIVE- used to distinguish from S.epidermidis and micrococcus
plasma clots by conversion of fibrinogen to fibrin
where is S.aureus normally found?
skin, nose
who does pneumonia and septicaemia caused by S.aureus affect most?
newborns and immunocompromised (eg burns)
how does S.aureus cause skin infections?
what does it cause?
invades subcutaneous tissue using LIPASES, causes inflammation, forms FIBRIN SACK, attract neutrophils to site, release LEUKOCIDIN that KILLS neutrophils—> PUS formed
causes furuncles, carbuncles and impetigo
what is septic arthiritis? what is it caused by ?
who does it affect?
caused by S.aureus, Strep.pyogenes
- infection of JOINT (via trauma/blood infection/surgery)
- babies, young children
what is osteomyelitis? what is it caused by ?
who does it affect?
caused by S.aureus
- infection of BONE
- direct INOCULATION OR
if bacteria are SEEDED FROM BLOOD- HEMATOGENOUS osteomyelitis
- commonly in children (fast growth of bone, blood can DEPOSIT bacteria)
what is responsible for Scalded Skin Syndrome? symptoms?
caused by S.aureus that is CARRYING A BACTERIOPHAGE which expresses exfoliatin toxin (A or B).
- symptoms remote from actual site of infection
- desquamation (skin peeling)
what causes Endocarditis? what does it affect?
S.aureus
affects heart tissue, valves.
roughly what % of us carry S.aureus? what about in hospitals?
25%
but higher in hospital 50-70% in hospital staff
what can be a cause of wound infections and absesses?
S.aureus
- commonly hospital acquired (nosocomial)
how are HEMOLYSINS used as a virulence factor?
TOXIN - can lyse erythrocytes & other cell types
how are LEUKOCIDINS used as a virulence factor?
TOXIN - acts on polymorphonuclear leukocytes & macrophages
how are EXFOLIATINS used as a virulence factor?
PLASMID- encodes skin toxin, causing peeling of epidermis
how are ENTEROTOXINS A, B & D used as virulence factors?
EXOTOXINS- cause food poisoning, severe vomiting and diarrhoea
- are heat stable- resist boiling
how is TSST-1 used as a virulence factor?
SUPERANTIGEN- stimulates T cells in a NON ANTIGEN SPECIFIC WAY to activate MACROPHAGES to release TNF/cytokines—> shock
how are LIPASES used as virulence factors?
LIPID HYDROLYSIING ENZYME- allows organisms to invade tissues
how are FIBROLYSINS used as virulence factors?
dissolves fibrin clots, causes SPREAD
how is EXTRACELLULAR COAGULASE used as a virulence factor?
involved in forming FIBRIN wall of absesses
what produces Panton Valentine Leukocidin?
where is it found to cause disease?
who does it affect?
bacteriophage carrying lukF and lukS genes produce Panton Valentine Leukocidin
- V INVASIVE soft tissue inf
- community acquired (sometimes hospital outbreaks)
- young and healthy
what is the mechanism of Panton Valentine Leukocidin?
acts w/ other leukocidins to LYSE HOST CELL MEMBRANES
causes invasive soft tissue inf
what is S.aureus naturally resistant to? why?
how do we target this?
resistant to PENICILLIN, as it prod penicillinase (naturally)
target: make synthetic penicillins: oxacillin, METHICILLIN
some strains of S.aureus are resistant to what?
what is the concern about this?
METHICILLIN (MRSA)
O cannot use Methicillin to treat
what is used to treat MRSA?
VANCOMYCIN- (also targets peptidoglycan synth)
what has been found to be resistant to Vancomycin?
how did this happen?
Enterococcus faecalis
- DNA cont Vacomycin resistance passed from Enterococcus into MRSA via CONJUGATION of plasmid
where is MRSA commonly found?
in HOSPITAL healthcare setting USUALLY
where is MRSA less commonly found? who does it affect?
community- (C-MRSA)
affects: immunocompetent but
INJECTING DRUG USER, MASSAGE PARLOURS, RUGBY, WRESTLING (close contact)
describe Staph. epidermidis
- non haemolytic
- coagulase -VE
where is Staph. epidermidis found?
very common on skin flora, gut and resp tract
how common are S.epidermidis infections?
less common than S.aureus
where are the major infections of Staph. epidermidis found in the body?
what type of infection?
catheters, shunts and prosthetic heart valves
NOSOCOMIAL
does Staph have low or high GC content?
low (firmicute)
is Staph a lactic acid bacteria?
yes
