Comparison of the E-test with agar dilution susceptibility test by using bacteroides fragilis

Kim, Hee Sun; Kim, Sung Kwang; Cha, Hwa Sun

Abstract

The susceptibilities of 45 clinical isolates of bacteroidis fragilis to cefaclor, ciproflxacin and imipenem were determined by new method, E-test (AB Bidisk, Solna, Sweden) and were compared with those from conventional agar dilution method by using brain heart infusion, Mueller-Hinton and Wilk:..s Chalgren agar plates. And the susceptibility of 60 clinical isolates of bacteroides fragilis group (B. fragilis 45 strains, B. distasonis 6 strains, B. ovatus 5 strains, B. thetaiotaomicron 4 strains) to 5 quinolones (ciprofloxacin, enoxacin, norfloxacin, ofloxacin, pefloxacin) were determined by in vitro agar dilution method. Compared with agar dilution MICs for B. fragilis 45 strains, 90.3% of E-test MICs were within +/- 1 dilution of the agar dilutions, and 98.4% were within 2 dilutions. And there were little effect of different medium bases to determine MICs except Mueller-Hinton agar. On Mueller-Hinton agar, B. fragilis showed have or no growth activity. In vitro susceptibility of B. fragilis group to quinolones, most of the test strains showed resistant patterns to quinolones except ofloxacin and there was little difference of susceptibility patterns between species of B. fragilis group.