Staphylococci Flashcards
Virulence factors for staph aureus
Protein A: binds ABs the wrong way, so neutrophils can’t get Fc region. Evasion: coagulase, catalase (convert H2O2 to H2O and O2), leukocidin; Tissue breakdown: Hyaluronidase, Staphylokinase, Lipases and proteases. Toxins: hemolysin, exfoliatin, enterotoxin, toxic shock toxin
How do we know it’s staph?
Gram + cocci, clusters on slide like grapes. On blood agar plate it is gold. All staph are catalase positive; do coagulase test (add colonies to plasma - clumping), clinches that it is staph aureus.
Symptoms of a S aureus infection
Fever, chills, diarrhea, vomiting, rash; High HR, low BP; Confusion, weakness; lesions around eyes, strawberry tongue; honey coloured crusting in skin infections. Depends on severity/extent of infection
TSST-1
Toxic Shock Syndrome Toxin. superantigen which non specifically stimulates T cells, resulting in a cytokine “storm”
Where do you want to sample for gram stain?
Exposed areas (ie if it’s exfoliating) and blood
Honey coloured clustering
When S. aureus produced a superficial infection, it causes purulent discharge. There is acute inflammation and lots of neutrophils. The discharge dries to a honey color. This superficial infection is AKA impetigo
Toxic shock in HIV patients?
Not so much b/c part of immune system is shot!
Food storing and staph
It can get in your food and grow there if it isn’t refrigerated, can produce toxins (esp enterotoxin) before you ingest it.
Other things caused be Staph aureus
Boil/abcess - Staph fights neutrophils (protein A, catalase to avoid destruction). Deep infections/bacteremia - breaks out of clots, and invades - meningitis, endocarditis, lungs, bones/joints. Impetigo - topical antibiotics, others if really sick.
Summary of pathogenesis
Colonization; Autoinoculation; Local infection; Immune response; Evasion; +/- Invasion (immunosuppressed, breech of barriers, prosthetic materials)
Amoxicillin
Amoxicillin binds PBP which crosslinks peptidoglycan so cell dies. Beta lactamase blocks amoxicillin, so we add clavulanate.
Tx for Penicillin allergy
Can use 1st generation cephalosporin. cloxacillin?? Vancomycin for MRSA. Directly binds peptidoglycan change.
Staph saprophyticus
coagulase negative. Causes UTI in young women
S epidermidis
Usual on skin. coagulase negative. likes to form biofilms on central venous catheters, artificial heart valves or prosthetic joints. Once in biofilm, only way to eliminate is removal of line etc.
