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Medical Microbiology Chapter 22 Staphylococcus and Related Organisms Gram+ Cocci Gram + Cocci (aerobic): Catalase + : Staphylococcus, Micrococcus, etc. Catalase - : Streptococcus, Enterococcus, etc. Staphylococcus Characteristics: Morphology Facultative anaerobes Tolerate high salt concentration (MSA) S. aureus produces coagulase Others are called coagulase negative staph Tables 22-1 and 22-2 Staphylococcus aureus Virulence Factors – Table 22-3 Staphylococcus aureus Epidemiology: Found on skin and anterior nares Easily shed from skin and nose • They can survive for long periods on dry surfaces • Can be spread by fomites Diseases Staphylococcal Scalded Skin Syndrome (Ritter’s Disease) – Figure 22-4 Bullous Impetigo – Figure 22-5 Food Poisoning Ham, salted meats, custard-filled pastries, potato salad, ice cream. Heat stable toxin Acute disease (4 hour incubation/~24 hour duration) Toxic Shock Syndrome – 6000 cases per year Initially very high mortality ~90% of adults have antibodies to the toxin More than 50% of TSS patients fail to produce antibodies Staph Skin Infections Infections of the hair follicles: folliculitis - small red bump at the site of infection • Stye – base of the eyelid furuncle (boil) - swelling, redness, severe tenderness and pain often with pus drainage carbuncle - furuncle that has spread and has several sites of draining pus • Figure 22-8 Staph Skin Infections Impetigo (pustular) Figure 22-7 Other Staph Infections Bacteremia – about 50% are nosocomial Endocarditis – 50% mortality rate Pneumonia Osteomyelitis – from bacteremia or wound spread Septic arthritis Staph ID and treatment Gram stain, catalase, coagulase, mannitol fermentation, etc. Penicillin resistance is common (~90% of all staph) MRSA is a growing concern