Chapter 130. Streptococcal and Enterococcal Infections (Part 11)

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Group B Streptococcal Infection in Adults: Treatment GBS is less sensitive to penicillin than GAS, requiring somewhat higher doses. Adults with serious localized infections (pneumonia, pyelonephritis, abscess) should receive doses of ~12 million units of penicillin G daily; patients with endocarditis or meningitis should receive 18–24 million units per day in divided doses. Vancomycin is an acceptable alternative for penicillin-allergic patients. Enterococci and Nonenterococcal Group D Streptococci Enterococci Lancefield group D includes the enterococci—organisms now classified in a separate genus from other streptococci—and nonenterococcal group D streptococci. ...

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Chapter 130. Streptococcal and Enterococcal Infections (Part 11) Group B Streptococcal Infection in Adults: Treatment GBS is less sensitive to penicillin than GAS, requiring somewhat higher doses. Adults with serious localized infections (pneumonia, pyelonephritis, abscess) should receive doses of ~12 million units of penicillin G daily; patients with endocarditis or meningitis should receive 18–24 million units per day in divided doses. Vancomycin is an acceptable alternative for penicillin-allergic patients. Enterococci and Nonenterococcal Group D Streptococci Enterococci
Lancefield group D includes the enterococci—organisms now classified in a separate genus from other streptococci—and nonenterococcal group D streptococci. Enterococci are distinguished from nonenterococcal group D streptococci by their ability to grow in the presence of 6.5% sodium chloride and by the results of other biochemical tests. The enterococcal species that are significant pathogens for humans are E. faecalis and E. faecium. Less commonly, similar infections are caused by E. casseliflavus, E. durans, E. gallinarum, or other enterococcal species. These organisms tend to affect patients who are elderly or debilitated, whose mucosal or epithelial barriers have been disrupted, or whose normal flora has been altered by antibiotic treatment. Urinary tract infections due to enterococci are quite common, particularly among patients who have received antibiotic treatment or undergone urinary tract instrumentation. Enterococci are a common cause of nosocomial bacteremia in patients with intravascular catheters and account for 10–20% of cases of bacterial endocarditis on both native and prosthetic valves. The presentation of enterococcal endocarditis is usually subacute but may be acute, with rapidly progressive valve destruction. Enterococci are frequently cultured from bile and are involved in infectious complications of biliary surgery and in liver abscesses. Moreover, enterococci are often isolated from polymicrobial infections arising from the bowel flora (e.g., intraabdominal abscesses), from abdominal surgical wounds, and from diabetic foot ulcers. While such mixed infections are frequently cured by antimicrobials not active against
enterococci, specific therapy directed against enterococci is warranted when these organisms predominate or are isolated from blood cultures. Enterococcal Infection: Treatment Unlike streptococci, enterococci are not reliably killed by penicillin or ampicillin alone at concentrations achieved clinically in the blood or tissues. Ampicillin reaches sufficiently high urinary concentrations to constitute adequate monotherapy for uncomplicated urinary tract infections. Because in vitro testing has shown evidence of synergistic killing of most enterococcal strains by the combination of penicillin or ampicillin with an aminoglycoside, combined therapy is recommended for enterococcal endocarditis and meningitis; the regimen is penicillin (3–4 million units every 4 h) or ampicillin (2 g every 4 h) plus moderate-dose gentamicin (1 mg/kg every 8 h for patients with normal renal function). Enterococcal endocarditis should be treated for at least 4 weeks and for 6 weeks if symptoms have been present for ≥3 months or if the infection involves a prosthetic valve. For nonendocarditis bacteremia and other serious enterococcal infections, it is not known whether the efficacy of a single β-lactam agent is improved by the addition of gentamicin, but many infectious disease specialists use combination therapy for such infections, especially in critically ill patients. Vancomycin, in combination with gentamicin, may be substituted for penicillin in allergic patients. Enterococci are resistant to all cephalosporins.
Antimicrobial susceptibility testing should be performed routinely on enterococcal isolates from serious infections, with therapy adjusted according to the results (Table 130-5). Most enterococci are resistant to streptomycin, which should not be used unless in vitro testing indicates susceptibility. Although less widespread than streptomycin resistance, high-level resistance to gentamicin— with a minimum inhibitory concentration (MIC) of >2000 µg/mL—is common. Gentamicin-resistant enterococci should be tested for streptomycin susceptibility, which they occasionally exhibit. If the isolate is resistant to all aminoglycosides, treatment with penicillin or ampicillin alone may be successful. Prolonged administration (i.e., for at least 6 weeks) of high-dose ampicillin (e.g., 12 g/d) is recommended for endocarditis due to these highly resistant enterococci. Table 130-5 Treatment Options for Antibiotic-Resistant Enterococcal Infections Resistance Pattern Recommended Therapy β-Lactamase production Gentamicin plus ampicillin/sulbactam, amoxicillin/clavulanate, imipenem, or vancomycin
β-Lactam resistance, but Gentamicin plus vancomycin no β-lactamase production High-level gentamicin Streptomycin-sensitive isolate: resistance Streptomycin plus ampicillin or vancomycin Streptomycin-resistant isolate: No proven therapy (continuous-infusion ampicillin, prolonged treatment) Vancomycin resistance Ampicillin plus gentamicin Vancomycin and β- No uniformly bactericidal drugs; linezolid lactam resistance (all enterococci) or quinupristin/dalfopristin (E. faecium only)