staphylococci Flashcards
three staphylococcus species
1) aureus
2) epidermidis
3) saprophyticus
staphylococcus shape and gram stain
all gram positive cocci
what is coagulase?
clots human/rabbit plasma by activating fibrinogen
which staph species are coagulase positive?
only aureus, the other two are negative
what is catalase?
converts peroxide to oxygen and water
is staph catalase positive or negative?
positive, in contrast to strep which is negative
what is the metabolic characterization of staph?
facultative anaerobe
S. aureus, where found?
- skin, mucous membranes, nares of normal individuals
- nasal passages up to 30-40%
S. aureus risk factors
- foreign bodies, catheters
- hospitalized/immunocompromised
- diabetes
- drug addiction
S aureus pathogenesis of toxin-mediated disease
- enterotoxins via food/tampon
- colonization/toxin production in host - colonization via fibrinogen/fibrinogen receptors on bacteria
important S. aureus toxins
- toxic shock syndrome toxin - toxic shock syndrome
- exfoliatins - scalded skin syndrome
S. aureus pathogenesis of invasive disease
- bacterial surface adhesion molecules bind to matrix proteins such as fibrinogen, fibronectin, collagen, and platelets
- matrix proteins found on damaged skin, disrupted airway epithelium, or endothelial cells in bloodstream
- after adhesion, colonization, evasion of host response, toxin synthesis, cell lysis, spreading to other sites
S. aureus toxins and enzymes for cell lysis
- alpha toxin - lyse membranes
- leukocidins - lysis of leukocytes
- proteases - breakdown of host proteins
- coagulase - clots human plasma
- staphylokinase - lysis of blood clot
- hyaluronidase - dissolve hyaluronic acid, component of matrix
- lipase - dissolve lipids and lipoproteins
S. aureus toxins and enzymes for evasion of host immune response
- protein A - cell wall protein binds to host IgG via Fc receptors, less complement-mediated killing, B-cell super antigen leading to defective production of IgM
- enterotoxins A-E, G-I, T-cell superantigens, blunting of T-cell response
- capsular polysaccharides - anti-phagocytic
- Eap (Map) - surface protein that impairs neutrophil recruitment
S. aureus toxin-mediated diseases
- food poisoning
- toxic shock syndrome
- staph scalded skin syndrome
S. aureus food poisoning causes and clinical syndromes
- enterotoxins A-E, G-I
- can resist boiling
- A and C are super antigens stimulating IL-1, IL-2, TNF
- nausea, vomiting, non-bloody diarrhea
S. aureus toxic shock syndrome causes and clinical syndromes
- enterotoxin F (TSST-1)
- tampon use or open wounds
- superantigen stimulates IL-1, 2, TNF
- fever, rash, desquamation of palms and soles, hypertension, shock
S. aureus scalded skin syndrome causes and clinical syndromes
- exfoliatins A and B
- only secreted by phage group II
- seen in infants
- erythematous skin, exfoliation
- epidermis detaching from dermis in response to toxin
immunological nature of S. aureus toxin mediated infections:
- most caused by super antigen effect so antibiotics often not effective by the time the syndrome is present
treatment of staph aureus invasive infections
- surgical drainage of abscesses
- synthetic penicillin, vancomycin as last resort
S. aureus colony color
yellow
S. epidermidis colony color
white
S. saprophyticus colony color
white
distinguishing S. epidermidis from S. saprophyticus
S. epidermidis is sensitive to novobiotin, which S. saprophyticus is not.
S epidermidis, where found?
skin, normal flora
who most susceptible to S. epidermidis?
neonates, patients with renal failure, immunocompromised
S. epidermidis pathogenesis
- colonizes prosthetic surfaces very efficiently
- bacteremia, but slower than S. aureus
- ## BIOFILM
S. epidermidis clinical syndromes
- low grade fever, pain, discomfort about prosthetics
- may be a contaminant in blood culture so treat patient, not culture
treatment for S. epidermidis:
- remove prosthetics if feasible
- vancomycin
- consider rifampin and/or gentamicin if toxic
S. saprophyticus clinical syndromes
- second most common cause of UTI after E. coli
- polyuria, dysuria
S. saprophyticus, where found?
skin
S. saprophyticus treatment
- trimethoprim sulfamethoxazol (bactrim)
- norfloxacin (quinolone)
