Staphylococcus Flashcards
Staphylococcus
Gram positive cocci, “bunches of grapes” appearance, facultative anaerobes, non-sporing. Catalase positive, coagulase positive, grow on MacConkey agar, non-fastidius (grow without special nutrient requirements) so they grown on simple media (nutrient agar). DNAse positive, beta hemolysis (alpha and beta hemolysins). Commensals of mucous membranes and skin of all warm-blooded animals. Survive well in the environment. Mastitis, wound infections, osteomyelitis, pyoderma, “greasy pig dz”, gangrenous dermatitis. **can infect any organ/tissue**
Staph virulence factors
ADHERANCE: Fibronectin-Binding Proteins. ANTI-CHEMOTAXIS: CHIPS (chemotaxis inhibitory proteins of staph). ANTI-OPSONIC/ANTI-PHAGOCYTIC: Protein A (binds Fc region of antibody, interferes with phagocytosis); SCIN (staph complement inhibitor, inhibits complement pathways); Capsule (not opsinised or phagocytosed); Fibrinogen binding protein (binds fibrinogen = masks itself and prevents opsonisation); Hemolysin + Leukocidin (inhibits or lyse phagocytes). IRON-UPTAKE SYSTEMS: siderophores, transferrin, lactoferrin. DEGREADATIVE ENZYMES: DNAse, Lipases, Proteases, Hyaluronidase. TOXINS: Exfoliative toxins (proteases that taget porteins only found in the epidermis), Superantigens (enterotoxins, toxic shock toxins-stimulate many T-cells with massive release of pro-inflammatory cytokines), Hemolysins (alpha-complete hemolysis immediately around colonies, and beta-incomplete hemolysis outside alpha zone).
Staph pathogenesis
Expression of adhesions results in adherence to extracellular matrix proteins. If the staph is not controlled and eliminated, capsule and toxin production increase, iron-uptake systems increase, and the infection progresses: supppuration and abscess formation; systemic effects may be seen and may be due to superantigen activity. Leading cause of bovine mastitis (S. aureus). Osteomyelitis, pyoderma in dogs/cats (S. pseudintermedius). Exudative epidermitis (“greasy pig dz”) (S. hyicus).
Staph diagnosis
Gram stain (positive cocci in pairs/cluster/”cluster of grapes”). Blood agar (hemolysis). Coagulase tests. Biochemical tests.
