Infections caused by anaerobic bacteria are common, and may be serious and life-threatening. Anaerobes predominant in the bacterial flora of normal human skin and mucous membranes, and are a common cause of bacterial infections of endogenous origin. Infections due to anaerobes can evolve all body systems and sites. The predominate ones include: abdominal, pelvic, respiratory, and skin and soft tissues infections. Because of their fastidious nature, they are difficult to isolate and are often overlooked. Failure to direct therapy against these organisms often leads to clinical failures. Their isolation requires appropriate methods of collection, transportation and cultivation of specimens. Treatment of anaerobic bacterial infection is complicated by the slow growth of these organisms, which makes diagnosis in the laboratory only possible after several days, by their often polymicrobial nature and by the growing resistance of anaerobic bacteria to antimicrobial agents.

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Sunday, December 22, 2013

Multidrug-Resistant Bacteroides fragilis isolated in the US

B. fragilis strains, especially in the US, are virtually always susceptible to metronidazole, carbapenems, and beta-lactam antibiotics. Although isolated cases of resistance to single agents have been reported, multidrug-resistant (MDR) B. fragilis strains are exceptionally rare. In May 2013, an MDR B. fragilis strain was isolated from the bloodstream and intra-abdominal abscesses of a patient who had recently received health care in India. The organism was resistant to metronidazole, imipenem, piperacillin/tazobactam, clindamycin, tcefotetan, ampicillin/sulbactam, and moxifloxacin. It was susceptible to minocycline, linezolid, and tigecycline. He was successfully treated with linezolid and ertapenem. This is only the second published case of MDR B. fragilis in the US.

Although B. fragilis has long been considered reliably susceptible to a number of broad-spectrum anti-anaerobic drugs, this case and others like it suggest clinicians should no longer rely on cumulative susceptibility data from surveys alone to direct treatment and should consider requesting susceptibility testing when treating serious infections caused by B. fraglis. They also underscore the need for improved antibiotic stewardship. 

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