Medical Microbiology Chapter 22 Staphylococcus and Related Organisms

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

Staphylococcus §Characteristics: l Morphology l Facultative anaerobes l Tolerate high salt concentration (MSA) l S. aureus produces coagulase l Others are called coagulase negative staph §Tables 22-1 and 22-2

Staphylococcus aureus §Virulence Factors – Table 22-3

Staphylococcus aureus §Epidemiology: l Found on skin and anterior nares l 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 l Ham, salted meats, custard-filled pastries, potato salad, ice cream. l Heat stable toxin l Acute disease (4 hour incubation/~24 hour duration) §Toxic Shock Syndrome – 6000 cases per year l Initially very high mortality l ~90% of adults have antibodies to the toxin l More than 50% of TSS patients fail to produce antibodies

Staph Skin Infections §Infections of the hair follicles: l folliculitis - small red bump at the site of infection Stye – base of the eyelid l furuncle (boil) - swelling, redness, severe tenderness and pain often with pus drainage l carbuncle - furuncle that has spread and has several sites of draining pus Figure 22-8

Staph Skin Infections §Impetigo (pustular) l 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) l MRSA is a growing concern