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Western University
Microbiology and Immunology
Microbiology and Immunology 2500A/B

Lecture 6: Staphylococci 09/19/2012 Staphylococci  "Staphyle" – Greek for Bunch of Grapes  Gram-positive, coccus shaped, facultative anaerobe (don’t need oxygen to grow)  Coagulase Positive Staphylococci o Staphylococcus aureus o "aureus" = Latin for gold  Coagulase Negative Staphylococci o Staphylococcus epidermidis o Staphylococcus saprophyticus o many other coagulase negative species The Pathogen: Staphylococcus aureus  An efficient colonizer of humans that doesn’t usually cause problems  Where does Staph like to colonize? – Anterior nares (nostrils) and skin  Carriers of S. aureus are healthy, asymptomatic people  Colonization leads to greater risk of infection, but prognosis is also generally better  Colonization: o Skin and mucous membranes, nose (about 30% of people are persistently colonized) o Spread person-person by direct or indirect contact o Fomites (inanimate objects capable of transmitting an infectious disease) e.g. towels, razors, bandages o resistant to high salt (skin) o S. aureus surface proteins bind host proteins using adhesins (e.g. fibronectin, collagen and elastin binding proteins) o Adhesins are also important in endocarditis  The leading cause of hospital-acquired (nosocomial) infections  In the United States: o Causes more than 10 million skin and soft tissue infections/year o About 94, 000 invasive infections (31.8 per 100,000) o About 19,000 deaths  Generally an extracellular pathogen  A “pyogenic” or pus-producing infection (pus – body mounting in immune response)  The “hallmark” of S. aureus infection is the abscess o Heat, redness, swelling, and pain o A collection of dead neutrophils (pus) due to infection  Abscesses can occur in any organ but are most frequent on the skin  Can cause major complications if the organisms spread from the abscess  Abscesses don’t typically heal on their own – require drainage and maybe antibiotics Staphylococcus aureus Virulence Factors  Why so many diseases?  S. aureus produces many virulence factors  Expression of the virulence factors is regulated  Surface virulence factors expressed during exponential growth  Secreted virulence factors (exotoxins) expressed during stationary phase  Generally, surface virulence factors are for colonization purposes, while secreted virulence factors are for invasion and spread Virulence Factors are Regulated Staphylococcus aureus Virulence Factors Immune evasion mechanisms  Resistance to phagocytosis o Protein A:- o S. aureus surface protein o Binds the Fc portion of IgG o Antibodies are bound in the incorrect orientation to be recognized by neutrophil Fc-receptor  Toxins that kill leukocytes o S. aureus can make a number of cytolytic toxins that kill white blood cells o Often called “hemolysins” because they can lyse red blood cells o Examples: alpha-toxin and leukocidins The Pathogen: Staphylococcus aureus o Actual targets of these toxins are likely white blood cells  Deep abscesses: o Not superficial but still localized – has a o Helps to protect S. aureus in abscesses and for spreading “focus” of infection o e.g. cellulitis, liver, lung, kidney, tooth, etc. o Wound or surgical infections o Symptoms may not be obvious and may be more “constitutional” (whole body) e.g. fevers, chills, malaise, etc. o Deep abcesses can become systemic  Systemic infections: o Often no single “focus” of infection o e.g. bacteremia/septicemia, pneumonia, osteomyelitis, endocarditis o Very
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