Antimicrobial resistance of clinical isolates of anaerobic bacteria from a regional hospital in Costa Rica

Abstract

From 28 clinical samples of a regional hospital in Costa Rica, 31 anaerobic bacterial strains were isolated through 12 months (year 2006). Anaerobic susceptibility test were performed to all isolates, using the reference agar dilution method, ATB-ANA system (bioMérieux), and E-test strips (AB Biodisk). Nineteen strains were identified as Bacteroides fragilis group, 6 as Eggerthella lenta, 3 as Propionibacterium sp. and 3 as Clostridium sp. All of the 19 strains of B. fragilis were metronidazole sensible (MIC of 0.25 a 2 µg/ml) and clindamycin resistant (MIC of 4 µg/ml to > 128 µg/ml); some strains showed high MICs: penicillin 512 µg/ml, cefotaxime 256 µg/ml, cephalotin 128 µg/ml and clindamycin 128 µg/ml). Very few of the Gram-positive rods were resistant to the antibiotics tested; however two strains showed MICs to metronidazole > 128 µg/ml.The high MICs to some antibiotics and the high resistance to clindamycin in the B. fragilis group strains are relevant findings considering their wide therapeutic use in Costa Rica. Several results obtained by the use of ATB-ANA were discrepant with those obtained when using agar dilution and E-test methods. On this basis, we recommend the use of E-test for routine testing and the agar dilution reference method for more accurate evaluations.