Investigations on Effects of Broilact - a Competitive Exclusion Product, on Antimicrobial Resistance in Commensal Escherichia coli and Enterococcus Isolates from Broiler Chickens

The present study was carried out to study phenotype resistance profiles and some genetic deter¬minants in resident Escherichia coli and Enterococcus bacteria isolated from chickens treated with the competitive exclusion product Broilact (Orion Pharma Animal Health, Finland). For bacteriological exam¬ination, anal swabs were collected at various time intervals throughout the study: from day-old, 14-day-old and 28-day-old chickens. The highest rate of resistance in E. coli isolated from experimental day-old chicks was observed against ampicillin and amoxicillin/clavulanic acid (42.8%), followed by resistance against tetracycline (30.9%), gentamicin (26.2%), and third-generation cephalosporins (21.4%). A broader preva¬lence (P≤0.05) of E. coli strains resistant against gentamicin (50%) and ciprofloxacin (31.2%) was found in control day-old chickens in comparison to birds in the respective experimental group (26.2%; 11.9%). E. coli strains isolated from the 14-day-old birds from both groups showed high resistance against all test¬ed chemotherapeutics: ampicillin (100%, 97.0%), tetracycline (91.8%, 97.0%) and ciprofloxacin (88.0%, 97.6%), followed by cefotaxime (83.7%, 93.1%), ceftazidime (95.9%, 91.8%), and gentamicin (83.7%, 87.7%). This tendency was also demonstrated by resistance patterns of E. coli isolated from both groups at 28 days of age. The prevalence of erythromycin-resistant enterococci isolated from day-old broiler chick¬ens was 62.0% in the control group and 48% in the experimental group. Next came tetracycline-resistant enterococci from control chickens (56%) vs 32% in the experimental group. The Enterococcus isolates from 14-day-old and 28-day-old birds in both groups exhibited also higher rates of resistance against eryth¬romycin (78.8%, 67.3%; 55.1%; 62.0%).