Chapter 129. Staphylococcal Infections (Part 9) pot

Chapter 129. Staphylococcal Infections (Part 9) Food Poisoning S. 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 other etiologies, especially that caused by similar toxins (e.g., the toxins 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 by the demonstration of bacteria or the documentation of enterotoxin in the implicated food. Treatment is entirely supportive. Staphylococcal Scalded-Skin Syndrome SSSS most often affects newborns and children. The illness may vary from localized blister formation to exfoliation of much of the skin surface. The skin is usually fragile and often tender, with thin-walled, fluid-filled bullae. Gentle pressure results in rupture of the lesions, leaving denuded underlying skin (Nikolsky's sign; Fig. 129-4). The mucous membranes are usually spared. In more generalized infection, there are often constitutional symptoms, including fever, lethargy, and irritability with poor feeding. Significant amounts of fluid can be lost in more extensive cases. Illness usually follows localized infection at one of a number of possible sites. SSSS is much less common among adults but can follow infections caused by exfoliative toxin–producing strains. Prevention Prevention of the spread of S. aureus infections in the hospital setting involves hand washing and careful attention to appropriate isolation procedures. Through strict isolation practices, some Scandinavian countries have been remarkably successful at preventing the introduction and dissemination of MRSA in hospitals. Other countries, such as the United States and Great Britain, have been less successful. The use of topical antimicrobial agents (e.g., mupirocin) to eliminate nasal colonization with S. aureus and to prevent subsequent infection has been investigated in a number of clinical settings. Elimination of nasal carriage of S. aureus has reduced the incidence of infections among patients undergoing hemodialysis and peritoneal dialysis. The prophylactic efficacy of topical mupirocin applied to the nares has been extensively investigated. While mupirocin eliminates nasal colonization with S. aureus, clinical trials to date have failed to demonstrate a subsequent reduction in the incidence of staphylococcal infections. A capsular polysaccharide–protein conjugate vaccine and antibodies to the ligand-binding domains of several MSCRAMMs (e.g., clumping factor) are under investigation. While in vivo studies have been promising in either preventing or reducing the incidence of infections, none of these vaccines has yet been successful for either prophylaxis or therapy. Coagulase-Negative Staphylococcal Infections CoNS, although considerably less virulent than S. aureus, are among the most common causes of prosthetic-device infections. Approximately half of the identified CoNS species have been associated with human infections. Of these species, S. epidermidis is the most common human pathogen overall; this component of the normal human flora is found on the skin (where it is the most abundant 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 associated with prosthetic-device infections. Infection is a two-step process, with initial adhesion to the device followed by colonization. S. epidermidis is uniquely adapted to colonize these devices by its capacity to elaborate the extracellular polysaccharide (glycocalyx or slime) that facilitates formation of a protective biofilm on the device surface. Implanted prosthetic material is often coated with host serum or tissue constituents such as fibrinogen or fibronectin. These molecules serve as potential bridging ligands, facilitating bacterial attachment to the device surface. A number of surface-associated proteins, such as autolysin (AtlE), fibrinogen-binding protein, and accumulation-associated protein (AAP), may play a role in attachment to either modified or unmodified prosthetic surfaces. The polysaccharide intercellular adhesin facilitates subsequent staphylococcal colonization and accumulation on the device surface. In S. epidermidis, ica genes are more commonly found in strains associated with device infections than in strains associated with colonization of mucosal surfaces. Biofilm appears to act as a barrier protecting bacteria from host defense mechanisms as well as from antibiotics, while providing a suitable environment for bacterial survival. Poly-γ- DL-glutamic acid is secreted by S. epidermidis and promotes protection against neutrophil phagocytosis. Two additional staphylococcal species, S. lugdunensis and S. schleiferi, produce more serious infections (native-valve endocarditis and osteomyelitis) than do other CoNS. The basis for this enhanced virulence is not known, although both species appear to share more virulence determinants with S. aureus (e.g., clumping factor and lipase) than do other CoNS. The capacity of S. saprophyticus to cause UTIs in young women appears to be related to its enhanced capacity to adhere to uroepithelial cells. A 160-kDa hemagglutinin/adhesin may contribute to this affinity. . Chapter 129. Staphylococcal Infections (Part 9) Food Poisoning S. aureus is among the most common causes of food-borne. or reducing the incidence of infections, none of these vaccines has yet been successful for either prophylaxis or therapy. Coagulase-Negative Staphylococcal Infections CoNS, although considerably. clinical trials to date have failed to demonstrate a subsequent reduction in the incidence of staphylococcal infections. A capsular polysaccharide–protein conjugate vaccine and antibodies to the ligand-binding