Staphylococci Flashcards
What are the main characteristics of staphylococcus?
Gram+
cocci
catalase+
What type of oxygen requirements does staphylococcus aureus need?
facultative anaerobe
What is catalase?
Reduces the potential of phagocytes to kill
What is coagulase?
coagulase binds prothrombin: fibrinogen is cleaved -> anti-phagocytic fibrin coating
- The tissue-invasive potential of staphylococcal infections is directly proportional to coagulase production (S.aureus)
What is clumping factor?
fibrinogen-binding protein: cell surface proteins that bind to foreign materials (like sutures) and to extracellular matrix
What is protein A?
Anti-phagocytic, competes with neutrophils for Fc portion of opsonizing IgG’s
- S aureus only (not other staphylococcal)
What is leukocidin?
- secretion: inhibits phagocytosis by granulocytes by forming pores in phagosomal membranes, and kills phagocytes
- Major factor in pus formation
What is staphylokinase?
converts plasminogen to plasmin, increasing invasion by digesting fibrin clots and cleaves C3b and IgG to inhibit phagocytosis
What is B-lactamase?
- Enzymatic digestion of penicillins
- (90% strains have plasmid-based antibiotic resistance)
What do hemolysins do?
lyse erythrocytes (lab phenomenon)
What type of hemolysis is complete erythrocyte lysis around all staphylococcus aureus colonies?
B-hemolysis
What type of staphylococcus experiences no hemolysis?
staphylococcus epidermidis
What is emphyema?
Collection of pus in a naturally- existing anatomical cavity (e.g. lungs)
What bacteria causes impetigo?
S. aureus
What are pyogenic infections?
pus-forming (massive amounts of neutrophils and other leukocytes are lysed by bacterial factors (e.g. leukocidin) and release their lysosomal contents in attempting phagocytic killing of the staphylococci).
What are the stages of an invasive pus-forming infection?
What is a superantigen?
overrides the specificity of the T-cell response
What are enterotoxins?
heat-stable toxins
- cause of gastrointestinal upset typical of food poisoning
What causes food poisioning?
enterotoxins
What is toxic shock syndrome toxin?
TSST: mass activation of T cells leads to large production of inflammatory cytokines (heat and protease-resistant TSST-1; chromosomal gene)
What is exfoliative toxin?
- (heat-stable, chromosomal)
- B (heat-labile, plasmid) : SSSS
(staphylococcal scalded-skin syndrome)
What is toxic shock syndrome (TSS)?
Increased oxygenation of vagina by tampons, and foreign surface adhesion, caused massive growth
What is staphylococcal scalded skin syndrome (SSSS)?
exfoliative toxins A, B cause loss of layers of the skin in SSSS -> Neutralizing Ab
What bacteria causes surgery, implant, and instrument risk?
nosocomial staphylococci
