Antimicrobial resistance in E. coli isolates from conventionally and organically reared poultry: A comparison of agar disc diffusion and Sensi Test Gram-negative methods

A total of 120 poultry carcasses (chicken, turkey and quail from conventional poultry farms, and chicken from organic farms; 30 samples in each group), collected from eight randomly selected retail outlets in North-Western Spain, was subjected to microbiological examination. Psychrotrophic counts ranged from 4.87 ± 0.83 log10 cfu/cm2 skin in quail to 6.01 ± 0.38 log10 cfu/cm2 skin in turkey. Higher (P < 0.05) faecal coliform load was found on conventionally produced chicken (2.95 ± 0.48 log10 cfu/cm2 skin) than in the other types of sample (from 1.71 ± 0.29 log10 cfu/cm2 skin in turkey to 2.19 ± 0.34 log10 cfu/cm2 skin in quail). All the samples harboured Escherichia coli. Sixty E. coli strains (15 from each type of sample) were tested for antimicrobial susceptibility using both the conventional agar disc diffusion method (12 antimicrobials) and a commercially available miniaturized test (Sensi Test Gram-negative). The disc diffusion method showed that 91.7% of isolates were multi-resistant (resistant to two or more antimicrobials). Resistance to nalidixic acid was the commonest finding (85.0% of strains), followed by resistance to ampicillin (75.0%), ciprofloxacin (73.3%) and tetracycline (61.7%). A significantly (P < 0.05) higher average number of resistances per strain was found in conventionally raised poultry (from 5.20 in chicken to 6.40 in quail) than in organic chicken (2.53). An agreement (kappa coefficient) of 0.74% was found between the two testing methods. Using the agar disc diffusion as the reference method, the sensitivity, specificity and accuracy of the miniaturized test were 71.52%, 97.60% and 89.63%, respectively. Findings in this study suggest a linkage between the use of antimicrobials on conventional poultry farms and selection for antimicrobial-resistant bacteria on meat, and highlight the need for the prudent use of antimicrobials with food-producing animals. Because poultry meat is an important reservoir of antimicrobial-resistant E. coli, the need for consumer education on good hygiene practices is emphasized.