Comparison of broth microdilution and disk diffusion test for antimicrobial resistance testing in Yersinia enterocolitica 4/O:3 strains.

The aim of this study was to compare the results obtained from two methods for the determination of antimicrobial resistance in 110 Yersinia enterocolitica 4/O:3 strains. Ten antimicrobial agents were tested using broth microdilution and disk diffusion. Similar results were determined for six antimicrobials. Very major errors (false-susceptible by disk diffusion test) were detected for ampicillin (at a rate of 1.8%). Major errors (false-resistant by disk diffusion test) were found for streptomycin (0.9%) and sulfamethoxazole (1.8%). Minor errors (intermediate susceptible by disk diffusion and resistant or susceptible by microdilution) were obtained for ampicillin (2.7%) and sulfamethoxazole (13.6%). All Y. enterocolitica were resistant to at least one antimicrobial agent. Resistances to three classes of antimicrobial agents were obtained by 3% of the strains included in the study. A slightly higher frequency of multiresistance was obtained by disk diffusion (3%) compared with broth microdilution (1%). Resistance to streptomycin was found frequently (13%); in contrast, resistance to tetracycline was rare (1%). The disk diffusion test produced unacceptably high rates of very major errors for ampicillin and a high frequency of minor errors for sulfamethoxazole. Susceptibility tests should thus be carried out by the more reliable method of microdilution. Most of the antimicrobials that can be used for therapy were very effective when tested against Y. enterocolitica. In order to identify changes in susceptibilities as early as possible, antimicrobial resistance in Y. enterocolitica should be regularly surveyed.