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Medical Microbiology
Chapter 22
Staphylococcus and Related Organisms
Gram+ Cocci
 Gram + Cocci (aerobic):
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Catalase + : Staphylococcus, Micrococcus,
etc.
Catalase - : Streptococcus, Enterococcus,
etc.
Staphylococcus
 Characteristics:
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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:
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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
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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
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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:
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folliculitis - small red bump at the site of infection
• Stye – base of the eyelid
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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)
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Figure 22-7
Other Staph Infections
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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