Asynchronous- microbiology W1- staphylococcus Classification of staphylococci · Kingdom: bacteria; Family: staphylococcaceae o (staphyle: bunches of grapes) · gram positive cocci: 0.5-1.0 micrometre in diameter · facultative anaerobes: 18- 40 degrees Celsius · catalase positive · approx. 40 species; skin and mucous membranes · major differentiating feature is COAG ULASE Classification of staphylococci: COAGULASE COAGULASE PRODUCTION Ability to coagulate citrated plasma yes 1 Coagulase-positive staphylococci Staphylococcus aureus no 1 Coagulase-negative staphylococci (CNS) 30+ species including: Staphylococcus epidermidis Staphylococcus saprophyticus · pathogenic staph (staph aureus) will be coagulase positive, whereas non-pathogenic staph (staph epidermidis/skin flora) will be negative for coagulase · coagulase converts fibrinogen into fibrin · forms a fibrin clot around pathogen (coagulase positive) o this is used as a defence mechanism- prevents antibiotics etc, from penetrating · staph saprophyticus- also negative coagulase o carried in female genital area o causes condition caused honeymoon cystitis staphylococcus aureus - virulence factors and mechanisms of pathogenicity staph aureus is an example of a true pathogen . ability to colonise the host and invade tissues · ability to evade host defences · ability to damage host through production of invasins and exocellular toxins · ability to acquire resistance to antibiotics schematic representation of virulence factors of S.aureus 2 Protein A Y- -IgG micro- capsule cell wall Toxins: TSST SE A- G. cell membrane damage toxic shock exfoliation emesis 3 Invasins: hyaluroni dase staphylysin- leukocidin- leukotoxin coagulase staphylokinase 3 fibrin fibronectin damaged tissue Adhesins: cell-bound proteins 1 1. colonisation of host (ADHESINS) · MSCRAMMS (microbial surface recognising adhesive matric molecules) o fl types: a) Expression of surface fibronectin and laminin binding proteins- fibronectin, laminin (and fibrogen) from the extracellular surface matrix of healthy endothelial and epithelial surfaces b) Expression of fibrin/fibrinogen binding proteins (clumping factor)- promotes adhesion to damaged tissues and blood clots c) Expression of collagen binding proteins- promotes adhesion to severely damaged tissue 2. Avoidance of host defences · Surrounded by a capsular polysaccharide o prevents cflb of the complement system from attaching to the organism preventing complement associated opsonisation. o Therefore, no phagocytosis · Protein A o Binds igG the wrong way around o Bind the Fc portion (preventing the antibody binding at the FAD component) Therefore, preventing complement associated opsonisation, phagocytosis Is an ‘antibody sponge' o · Leucocidin production o Pore-forming, bursts open the white blood cells
o The genes for this toxin are carried by a bacteriophage and injected into staph chromosome The toxin is called PVL (Panton Valentine Leucocidin)- most lethal o This toxin is produced from community strains of staph (very rare in hospitals) 3. Invasion of host tissue (INVASINS) · Membrane damaging toxins E.g. Alpha-haemolysin o Pore forming toxin that attaches to lipid membranes of wbc and rbc o Causes cells to spill contents through pores o Called a type II toxin because it works on the membrane of cells · Coagulase o Clotting o Protective factor · Staphylokinase o When bacterium wants to continue moving it breaks down fibrin that is formed by coagulase (fibrinolysis)