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Gram –Positive cocci Staphylococcus Introduction: )Staphylococcus aureus (yellow Genus: Staphylococcus Family: Micrococcaceae (see table 1) Species: Staphylococcus aureus (most medically important species). It can causes serious bacterial infections, intoxication, food poisoning, toxic shook syndrome Others: Staphylococcus epidermidis Staphylococcus saprophyticus Staphylococcus haemolyticus Definition :staphylococcus aureus are Gram positive and occur characteristically in irregular grape-like clusters . Normal habitat:* S. aureus is carried in the nose of 40% or more of healthy people. Epidemiology Carriers serve as a source of infection to themselves and others e.g. : Direct contact By contamination of vomits Or food which results to food poisoning Nosocomial infection Phathogenicity: 1. Common cause of primary localized skin infections including 2. Deep, localized infections these maybe metastatic from superficial infections or skin, or trauma ostomyelitis (bown marrow infection) Arthritis (infection of the joints) 3. Acute endocarditis associated with intravenous drug abuse 4. Septicemia: generalized infection with sepsis or bacteremia 5. Pneumonia and empyema 6. Nosocomial infection its one of the most common cause of hospital acquired infections 7. osteomyelitis 8. artharitis 9. Toxinoses A. toxic shock syndrome : TSS : B. staphylococcus gastroenteritis: is caused by ingestion of food contaminated with enter toxin, usually contaminated by a food handler these food tend to be protein rich for example egg salad, cream pastry, ice cream, and improperly refrigerated, symptom are nausea vomiting and diarrhea after short period of incubation like 6 hours C. scalded skin syndrome (Lyell’s syndrome), Virulence factors Enzymes and toxins produced by S. aureus 1. Cell wall virulence factor Protein A Fibronectin-binding protein FNBP 2. Cytolytic exotoxins ∞, ß, γ, 3. superantigen exotoxins: 4. enterotocxins : six major antigen types A, B, C, D, E, and G) 5. Coagulase •Deoxyribonuclease (DNAse), that destroys DNA •Hyaluronidase, that helps S. aureus to spread in the tissues •Lipase, that breaks down fat •Staphylokinase, that causes fibrinolysis •Exofoliatin, that causes peeling of the skin •Enterotoxin B, that causes food poisoning •Beta-lactamase (antibiotic-inactivating enzymes), that lead to Penicillin resistance. •Capsular Polysaccharide •Leukocidin FIGURE 2. Virulence determinants of Staphylococcus aureus laboratory diagnosis : Specimens : Pus Sputum Blood Faeces If food poisoning suspected (vomiting) Anterior nasal swap required to detect S. aureus carrier Swaps from different site infected. Portion of intravenous device Direct Microscopy Culture: Temperature: optimal (33-37ºC) temperature range (10-42ºC) Atomospher: aerobically also in carbon-dioxide, most trains grow anerobically. Time: over night 24 hrs. Different media Nutrient agar Blood agar (Golden yellow- with B-haemolysis when grown areobically) for and other than S. aureus are white colonies, all easy to emulsify. MacConckey: small colonies which are pink in color due to lactose fermentation. Most strains are non-lactose fermented. Manitol salt agar : Biochemical reaction Coagulase test This test is used to differentiate S. aureus form S. epidermidis and S. saprophyticus. Free Coagulase Bound Coagulase II. DNAse If plasma is not available or the Coagulase test are not clear. This test is used to differentiate S. aureus which produces the enzyme DNAse from other staphylococci which don’t produce DNAse. Catalase test: To differentiate staphylococcus species are catalase positive where from streptococcus species are catalase negative. Antimicrobial sensitivity Penicillin resistance most of staph are resistance to penicillin G . This has required the replacement of the initial agent of choice, penicillin G by B-lactamase – resistance penicillin such as nafcillin or oxacillin Methecillin resistant test: Medium is trypticase soya agar salt (TSA) MRSA: methecillin resistant S. aureus MSSA. Methecillin sensitive S. aureus vancomycin : the drug of choice for MRSA, but the possibility that this resistance my increase in strength spread to other species prevention there is no effective vaccines against S. aureus so infection control procedures such as barier precautions, washing hands and vomits are important in control of nosocomial infection,