Objectives:

The antimicrobial resistance surveillance of Gram-negative anaerobic bacteria isolated in six Greek hospitals.

Methods:

A total of 122 Gram-negative anaerobic clinical strains (72 Bacteroides fragilis group, 17 other Bacteroides spp. non-fragilis, 25 Prevotella spp., 4 Fusobacterium spp. and 4 miscellaneous) isolated during the period November 2002 to November 2003 were tested using the Etest method on brucella blood agar plates. Incubation in a ChelLab 1.5 Anaerobic Chamber was performed for 48 h and interpretation was according to NCCLS guidelines.

Results:

Overall Gram-negative non-susceptible (intermediate and fully resistant) rates to penicillin, ticarcillin + clavulanic acid, cefoxitin, tetracycline, clindamycin, metronidazole, imipenem and ertapenem were 83, 2, 31, 55, 32, 6, 1 and 5%, respectively. Bacteroides fragilis group rates were 93, 4, 38, 65, 31, 1, 1 and 7%, respectively. Prevotella spp. rates were 68, 0, 8, 32, 36, 16, 0 and 0%, respectively. Overall Gram-negative MIC90s were 256, 2, 64, 128, 256, 2, 0.5 and 1 mg/L, respectively. Bacteroides fragilis group MIC90s were 256, 4, 128, 128, 256, 1, 1 and 4, respectively. Prevotella spp. MIC90s were 256, 1, 16, 64, 256, 256, 0.125 and 0.5, respectively. Metronidazole resistance was detected among four Prevotella spp., one Bacteroides spp., one Porphyromonas spp. and one Fusobacterium spp. isolates. Additionally, a B. fragilis strain was found highly resistant (MIC > 32 mg/L) both to imipenem and ertapenem and resistant to all other antimicrobials tested except metronidazole.

Conclusions:

Carbapenems, beta-lactam + inhibitor combinations and metronidazole remain the antimicrobial agents of choice against most Gram-negative anaerobes. However, metronidazole resistance seems to be an emerging problem in Greece, especially among Prevotella spp. isolates. In that respect species identification and periodic susceptibility surveillance is mandatory. Imipenem and ertapenem activity was comparable, though ertapenem MICs were slightly higher.

Acknowledgements:

Members of the Hellenic Study Group for Gram Negative Anaerobic Bacteria are Drs A. Avlamis, C. Koutsia-Karouzou, C. Kontou-Kastelanou, A. Pangalis, E. Papafrangas and E. Trika-Grafakos.