Comparison of methods for the determination of antimicrobial resistance in Campylobacter spp. human and the food chain isolates

With a microdilution method, using the commercial diagnostic test Sensititre Susceptibility Plates for Campylobacter MIC (Trek Diagnostic Systems, Cleveland, OH, USA), disk diffusion and agar dilution method, resistance to six antimicrobial agents were examined in a reference strain Campylobacter jejuni ATCC 33560 and 73 thermo-tolerant isolates of Campylobacter spp. For the microdilution method and all tested antimicrobial agents, our determined values of microbiological breakpoints of resistant strains were suggested as the minimum inhibitory concentration (MICR) for ciprofloxacin ≥ 0.5, erythromycin ≥ 4, gentamicin ≥ 4, nalidixic acid ≥ 32 and tetracycline ≥ 4 μg/ml. On the basis of our study results, strains resistant to clindamycin were MICR ≥ 2 μg/ml for the dilution methods and a zone diameterR ≤ 16 mm for the disk diffusion method. Comparison of the results of the resistance examination, a microdilution method and disk diffusion method with the reference agar dilution method, showed that all compared methods yielded identical results with the exception of the resistance determination in erythromycin and nalidixic acid. The errors were mostly the result of the interpretation criteria for MICR of agar dilution method and different conditions of cultivation used. However, the compared methods, provide results comparable with the reference method having greater convenience of measurement.