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...

High resistance rates to moxifloxacin among Bacteroides and Prevotella spp. were recorded, exceeding those previously reported in Europe and contraindicating its use as monotherapy for infections involving Gram-negative anaerobes without prior microbiological confirmation. For empirical usage, moxifloxacin should be combined with metronidazole in order to cover for these pathogens.

The in-vitro activities of penicillin, ticarcillin-clavulanic acid, cefoxitin, imipenem, ertapenem, metronidazole and clindamycin were evaluated against 138 Gram-negative anaerobic isolates (82 Bacteroides fragilis group, 17 non-fragilis Bacteroides spp., 31 Prevotella spp., four Fusobacterium spp., two Veillonella spp., one Porphyromonas sp. and one Tissierella praeacuta) collected from six general hospitals in Athens, Greece. Overall rates of non-susceptibility (both resistant and intermediately-resistant) to penicillin and ticarcillin-clavulanic acid were 81.8% and 2.3%, respectively. The rates of non-susceptibility to cefoxitin and clindamycin were 30.3% and 31.1%, respectively, and that for metronidazole was 4.3% (four Prevotella spp. isolates, one Porphyromonas sp. isolate and one B. fragilis isolate). Only the single B. fragilis isolate was nim-positive by PCR. Only one B. fragilis isolate was resistant to both carbapenems tested, while six more Bacteroides spp. isolates were imipenem-susceptible and ertapenem-non-susceptible. The MIC range, MIC(50) and MIC(90) values were comparable for imipenem and ertapenem, although ertapenem MIC(90)s were one or two two-fold dilutions higher.

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