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Medical Microbiology

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

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Medical Microbiology

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  1. Medical Microbiology Chapter 22 Staphylococcus and Related Organisms

  2. Gram+ Cocci • Gram + Cocci (aerobic): • Catalase + : Staphylococcus, Micrococcus, etc. • Catalase - : Streptococcus, Enterococcus, etc.

  3. 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

  4. Staphylococcus aureus • Virulence Factors – Table 22-3

  5. 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

  6. 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

  7. 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

  8. Staph Skin Infections • Impetigo (pustular) • Figure 22-7

  9. Other Staph Infections • Bacteremia – about 50% are nosocomial • Endocarditis – 50% mortality rate • Pneumonia • Osteomyelitis – from bacteremia or wound spread • Septic arthritis

  10. Staph ID and treatment • Gram stain, catalase, coagulase, mannitol fermentation, etc. • Penicillin resistance is common (~90% of all staph) • MRSA is a growing concern

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