Staphylococci

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Staphylococci Characteristics

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Pyognenic, coagulase positive S aureaus, or coagulase negative, memberes of the micrococcaceae family which includes S.epidermidis or S. saprophyticus, extremely hardy, do not form spurs, gram positive cooci that grow in clusters.

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Identifying Staphylococci

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-bunch of grapes
-soft round convex colonies on agar, S. aureus is golden
-all are catalase positive

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Identifying Gram Positive Cocci

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Step 1: Catalase test, if positive than micrococcaceae, if negative streptococcacae

Step 2: Coagulase, if positive S, aureus, if negative S. Epidermidis and S. hemolyticus

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Structural Comppnents of S. Aureus

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Fibronectin, collagen, elastin binding proteins, protein A, coagulase, clumping factor, capsule, peptidoglycan cell wall

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Secreted Products of S. Aureus

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Catalase, Coagulase which converts fibrinogen to fibrin, hyaluronidases facilitating spread, lipases for lipids, and beta-lactamases against penicillin

Toxins such as TSS-2 that cause food poisoning, exfoliative toxins that cause scalded skin

Membrane damaging tocins like leukocidin in pulmonary infection and alpha toxin which damages membranes

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Alpha Toxin mechanism

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Aplha toxin is a monomer with an insertion sequence that binds membranes and ogliomerizes forming a prepore that then fully inserts forming a pore.

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Epidemiology of S. Aureus

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Humans are primary reservoir with auto-innoculation being common, though in some hospital straisn it can be person to person and hospital kind can be traced to staphyloccocal cloud single strain, increase in MRSA.

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Diseases caused by S. Aureus

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skin/tissue infection, bacteremia and sepsis, endocarditis, musculoskeletal and respiratory infections , TSST-1 Scalded skin and TSS- food poisioning

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Pathogenous of Staph aureus Infection

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Colonization, Infection, invasion (local or systemic), and host response (PMNs, thrombosis and necrosis, abcess)

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S. Aureus as a Commensal

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Colonize the nares usually in 20-40% of individuals, toxin-mediated diseae sometimes without infection, may reduce infection by eleiminating carriage but there is potetial antibiotic resistance. Higher levels of colonization in drug users, diabetics, dialysis patients

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TSST

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Toxic Shock Syndrime Toxin 1 is expressed by S. aureus, it is on a chromosome in a mobile element. It is a superantigen that binds the MHC outisde of the T-cell binding pocket and causes massive T cell activation which leads to inflammation and cytokine release as well as liver damage that leads to less clearance of endotoxin and potentially shock

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Staph Food Posioning

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Does not require live pathogen just viable enterotoxin, it stimulates the vagus nerve in the venter controlling vomiting and increased peristalsis

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MRSA

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Increase in community outbreak, increased boils in Asians, increased in nose, increased in saunas, and mostly PVL positive, and sports teams

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Staphylococci Epidermidis

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normal commensal bacteria of the skin, coagulase negative, niche of infection is prosthetics and a frequent contaminat in cultures