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.

We report a case of septic arthritis due to Roseomonas mucosa in a rheumatoid arthritis patient receiving infliximab therapy. This is the first report of septic arthritis due to R. mucosa, and infliximab therapy might be a predisposing factor because this infection was never reported in the pre-anti-tumor necrosis factor alpha therapy period.

The in vitro activity of tigecycline was compared with those of benzylpenicillin, piperacillin + tazobactam, cefoxitin, imipenem, metronidazole, clindamycin, and tetracycline against 249 Gram-negative anaerobic bacteria (158 Bacteroides fragilis group, 27 non-fragilis Bacteroides spp., 44 Prevotella spp., and 20 miscellaneous), recently isolated from 8 general hospitals in Athens, Greece. Overall tigecycline MIC(50) and MIC(90) were 0.25 and 2 mg/L, respectively, whereas B. fragilis group MIC(50) and MIC(90) were 0.5 and 4 mg/L, respectively. In total, 93% of the isolates were susceptible to tigecycline (MIC /= 32 mg/L) was detected. In addition, tigecycline exhibited good activity against metronidazole- and tetracycline-resistant isolates (MIC(90), 0.5 and 8 mg/L, respectively). In summary, tigecycline exhibits good in vitro activity against Gram-negative anaerobic bacteria isolated in Greece, as well as stability to the most common occurring resistance mechanisms, attributes that make this parenteral agent an attractive alternative for use against infections involving these microorganisms.