Chapter 129. Staphylococcal Infections (Part 9)

Food PoisoningS. aureus is among the most common causes of food-borne outbreaks of infection in the United States. S. aureus food poisoning results from the inoculation of toxin-producing S. aureus into food by colonized food handlers. Toxin is then elaborated in such growth-promoting food as custards, potato salad, or processed meats. Even if the bacteria are killed by warming, the heat-stable toxin is not destroyed. The onset of illness is rapid, occurring within 1–6 h of ingestion. The illness is characterized by nausea and vomiting, although diarrhea, hypotension, and dehydration may also occur. The differential diagnosis includes diarrhea of...
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Chapter 129. Staphylococcal Infections (Part 9) Chapter 129. Staphylococcal Infections (Part 9) Food Poisoning S. aureus is among the most common causes of food-borne outbreaks ofinfection in the United States. S. aureus food poisoning results from theinoculation of toxin-producing S. aureus into food by colonized food handlers.Toxin is then elaborated in such growth-promoting food as custards, potato salad,or processed meats. Even if the bacteria are killed by warming, the heat-stabletoxin is not destroyed. The onset of illness is rapid, occurring within 1–6 h ofingestion. The illness is characterized by nausea and vomiting, although diarrhea,hypotension, and dehydration may also occur. The differential diagnosis includesdiarrhea of other etiologies, especially that caused by similar toxins (e.g., thetoxins elaborated by Bacillus cereus). The rapidity of onset, the absence of fever,and the epidemic nature of the presentation arouse suspicion of food poisoning.Symptoms generally resolve within 8–10 h. The diagnosis can be established bythe demonstration of bacteria or the documentation of enterotoxin in theimplicated food. Treatment is entirely supportive. Staphylococcal Scalded-Skin Syndrome SSSS most often affects newborns and children. The illness may vary fromlocalized blister formation to exfoliation of much of the skin surface. The skin isusually fragile and often tender, with thin-walled, fluid-filled bullae. Gentlepressure results in rupture of the lesions, leaving denuded underlying skin(Nikolskys sign; Fig. 129-4). The mucous membranes are usually spared. In moregeneralized infection, there are often constitutional symptoms, including fever,lethargy, and irritability with poor feeding. Significant amounts of fluid can be lostin more extensive cases. Illness usually follows localized infection at one of anumber of possible sites. SSSS is much less common among adults but can followinfections caused by exfoliative toxin–producing strains. Prevention Prevention of the spread of S. aureus infections in the hospital settinginvolves hand washing and careful attention to appropriate isolation procedures.Through strict isolation practices, some Scandinavian countries have beenremarkably successful at preventing the introduction and dissemination of MRSAin hospitals. Other countries, such as the United States and Great Britain, havebeen less successful. The use of topical antimicrobial agents (e.g., mupirocin) to eliminate nasalcolonization with S. aureus and to prevent subsequent infection has beeninvestigated in a number of clinical settings. Elimination of nasal carriage of S.aureus has reduced the incidence of infections among patients undergoinghemodialysis and peritoneal dialysis. The prophylactic efficacy of topicalmupirocin applied to the nares has been extensively investigated. While mupirocineliminates nasal colonization with S. aureus, clinical trials to date have failed todemonstrate a subsequent reduction in the incidence of staphylococcal infections. A capsular polysaccharide–protein conjugate vaccine and antibodies to theligand-binding domains of several MSCRAMMs (e.g., clumping factor) are underinvestigation. While in vivo studies have been promising in either preventing orreducing the incidence of infections, none of these vaccines has yet beensuccessful for either prophylaxis or therapy. Coagulase-Negative Staphylococcal Infections CoNS, although considerably less virulent than S. aureus, are among themost common causes of prosthetic-device infections. Approximately half of theidentified CoNS species have been associated with human infections. Of thesespecies, S. epidermidis is the most common human pathogen overall; thiscomponent of the normal human flora is found on the skin (where it is the mostabundant bacterial species) as well as in the oropharynx and vagina.S. saprophyticus, a novobiocin-resistant species, is a pathogen in UTIs. Pathogenesis Among CoNS, S. epidermidis is the species most commonly associatedwith prosthetic-device infections. Infection is a two-step process, with initialadhesion to the device followed by colonization. S. epidermidis is uniquelyadapted to colonize these devices by its capacity to elaborate the extracellularpolysaccharide (glycocalyx or slime) that facilitates formation of a protectivebiofilm on the device surface. Implanted prosthetic material is often coated with host serum or tissueconstituents such as fibrinogen or fibronectin. These molecules serve as potentialbridging ligands, facilitating bacterial attachment to the device surface. A numberof surface-associated proteins, such as autolysin (AtlE), fibrinogen-bindingprotein, and accumulation-asso ...