Comparison of Broth Microdilution, E Test, and Agar Dilution Methods for Antibiotic Susceptibility Testing of Campylobacter jejuni and Campylobacter coli

Abstract

A standardized broth microdilution method was compared to the E test and an agar dilution method for the antimicrobial susceptibility testing of Campylobacter jejuni and C. coli isolates. A group of 47 human clinical isolates, 37 isolates from retail poultry, and 29 isolates from living turkeys (total, 113 isolates) was included in the study. These encompassed 92 C. jejuni and 21 C. coli strains. The MICs of six antimicrobial agents were determined by the broth microdilution and E test methods, and the strains of human origin were additionally tested by the agar dilution method. In general, broth microdilution MICs agreed within 1 log 2 MIC increment with 90.0% of E test results and 78.7% of agar dilution test results. The agar dilution method gave much lower gentamicin MICs than the broth microdilution method, but the data were significantly (P < 0.01) correlated and there was 100% agreement in the sensitivities and specificities in the comparison of the tests. The broth microdilution method had the highest sensitivity for analysis of the susceptibilities of Campylobacter to nalidixic acid and trimethoprim-sulfamethoxazole. The MICs of ciprofloxacin and erythromycin complied numerically by all three methods. The classification of the results and the correlation of the data demonstrated a high degree of agreement. All methods were equally suitable for the testing of the sensitivity of Campylobacter to tetracycline. Thus, the broth microdilution method appears to be an easy and reliable method for determination of the MICs of antibiotics for C. jejuni and C. coli, and it may offer an interesting alternative to MIC determination by the agar dilution technique or the E test.

Antimicrobial resistance in Campylobacter spp isolated from broiler flocks

“…There are no parameters for the susceptibility profile of Campylobacter spp. (2,5), thus the interpretation of results an inhibition zone diameters followed the National Committee for Clinical Laboratory recommendations (8) for microorganisms requiring 5% CO2 for growth. The following bacteria were considered: Enterococcus for penicillin, amoxicillin and ampicillin, Streptococcus for tetracyclines and erythromycin, and Enterobacteriaceae for enrofloxacin.…”

“…It was not possible to measure the activity of the other antimicrobials and the TTC control disc, since there was no growth around the discs. The use of MH agar supplemented with 5% sheep blood (3,5) has been recommended in the literature. MH agar diffusion test compared to agar dilution test was considered to be reliable, easy-to-perform and inexpensive in monitoring the antimicrobial resistance of C. jejuni strains (2).…”

Campylobacter

“…Several laboratory methods, including disc diffusion, broth microdilution, agar dilution and the Epsilometer-test (E-test) have been applied to determine in vitro susceptibility profile(s) of Campylobacter to a range of antimicrobial agents [15,41,45,46,48,84,119,149]. Despite the availability of comparable standardised procedures for many organisms, based on, the approved guidelines defined by the National Committee for Clinical Laboratory Standards (NCCLS), no internationally accepted criteria for susceptibility testing of Campylobacter spp.…”

“…Values determined however can vary depending on the antimicrobial agent(s) being considered [48]. This observation was particularly evident with respect to C. jejuni [84]. Comparing MIC values obtained by E-test and the agar dilution protocols, Ge et al [48] reported values ranging from 21.4 to 62% for gentamicin and nalidixic acid respectively.…”

“…However when E-test and the agar dilution method are used on a small number of isolates from a single geographic location, acceptable agreement between both approaches for susceptibility categorisation is achieved. For larger collections, microdilution is the preferred protocol especially when susceptibility to nalidixic acid and trimethoprimsulfamethoxazole are being considered [84].…”