Two Cases of Infections Due to Multidrug-Resistant Bacteroides fragilis Group Strains

Abstract

Bacteroides fragilis group strains are still considered susceptible to most antimicrobial agents used for the treatment of infections caused by anaerobic organisms. We describe two cases of infections due to isolates simultaneously resistant to clindamycin, tetracycline, cefoxitin, piperacillin-tazobactam, and imipenem and, in one of the two cases, to metronidazole. Such infections, although still rare, do exist and tend to complicate treatment. First case report.A 71-year-old man was admitted to the internal medicine ward of Laikon General Hospital, a university-affiliated, tertiary-care hospital in downtown Athens, Greece, with a temperature of up to 39°C and diarrhea for 8 days. The patient's medical history included Crohn's disease; stomach lymphoma, which had led to a total gastrectomy 15 years earlier; common variable immunodeficiency; and cytomegalovirus (CMV) colitis.The patient's blood cell count was within the normal range, and serum biochemistry revealed only an elevated C-reactive protein level (280 mg/liter; normal values, Ͻ50 mg/liter). Computed tomography scanning of the upper and lower abdomen was negative, while a colonoscopy revealed findings consistent with CMV colitis. Blood samples for culture were taken on admission; and after 2 days of incubation, the anaerobic bottle (BacT/ALERT 3D; bioMerieux, Marcy l'Etoile, France) yielded a gram-negative anaerobic rod that was identified as Bacteroides fragilis by the special-potency disk method; growth in the presence of 20% bile (Bacteroides-bile esculin agar plates; Bioprepare, Gerakas, Greece); and the biochemical profile (ID32ANA system; bioMerieux), including a negative reaction for indole (7). Cultures of stool samples were negative for pathogens.Upon receipt of the preliminary finding of bacteremia caused by an anaerobic gram-negative organism, antimicrobial treatment was initiated with metronidazole three times daily at 500 mg intravenously (i.v.) and cefotaxime three times daily at 2 g i.v., after which the fever subsided but the diarrhea persisted, because of his underlying disease. His condition deteriorated during the following weeks, as he developed liver cirrhosis, ascites, and CMV pulmonary infiltrations. The patient died after 3 months of hospitalization due to pulmonary edema.Susceptibility testing of the B. fragilis isolate was performed by the Etest method (AB Biodisk, Solna, Sweden), according to the manufacturer's instructions, on brucella blood agar plates supplemented with vitamin K and hemin. The resulting MICs were Ͼ256 mg/liter for benzylpenicillin, piperacillin-tazobactam, ticarcillin-clavulanic acid, cefoxitin, and clindamycin; Ͼ32 mg/liter for imipenem and ertapenem; 128 mg/liter for tetracycline; and 0.5 mg/liter for metronidazole. The strain was positive for beta-lactamase production by the nitrocefin disk method (Cefinase; BBL, Becton Dickinson and Co., Franklin Lakes, NJ). The imipenem, ertapenem, and metronidazole MICs were confirmed by the agar dilution method (11). All plates used for susceptibility testing were in...

Multidrug-resistant Bacteroides fragilis group on the rise in Europe?

“…In the study of Katsandri et al (2006), it was shown in the first case described that the strain was metronidazolesusceptible but imipenem-resistant, and the authors detected a cfiA gene, which is associated with carbapenem resistance. There was no further description and no information about IS elements.…”

Antianaerobic Antimicrobials: Spectrum and Susceptibility Testing

“…Although rare, resistance to metronidazole among B. fragilis group isolates has been observed worldwide (33,135). Resistant B. fragilis group isolates carry one of nine known nim genes (nimA-I) on either the chromosome or a mobilizable plasmid that seems to encode a nitroimidazole reductase, which converts 4-or 5-Ni to 4-or 5-aminoimidazole, preventing the formation of toxic nitroso residues necessary for the agent's activity.…”

Development of EUCAST disk diffusion method for susceptibility testing of the Bacteroides fragilis group isolates

“…Additionally there are clear differences in the resistance according to the geographical areas [1] and even differences can be found in resistance patterns in different hospitals in a single city, which may be due to the variability in selecting antibiotics for empirical treatment [2]. Several papers reported about cases caused by broadly multidrug-resistant B. fragilis isolates [6,7,16,17], as well as number of reports describes the development of resistance in vitro or in vivo in the presence of antibiotics [18,19]. These events emphasize the need for antimicrobial susceptibility testing of anaerobes not only during periodical surveillances in different geographical areas, but also during the everyday routine laboratory testing.…”