Antimicrobial drug resistance of enteric bacteria from broilers fed antimicrobial growth enhancers and exposed poultry abattoir workers

Abstract

The usage of antimicrobials either as performance enhancers or for prophylactic and therapeutic purposes in food animals, such as chickens, increases the prevalence of antimicrobial drug resistance among enteric bacteria of these animals. This may be transferred to people working with such animals, e.g. abattoir workers, or the products arising from these animals. In this study antimicrobial drug resistance was investigated for selected enteric bacteria from broilers raised on feed supplemented with antimicrobial growth enhancers, and the people who carry out evisceration, washing and packing of intestines in a high throughput poultry abattoir in Gauteng, South Africa. Poultry farms (n=6) were purposively selected on the basis of allowing for sampling of farms from more than one grow out cycle. Broiler carcases (n=100) were randomly selected per farm five minutes after slaughter and sampled by incising caecae from the rest of the gastro-intestinal tract (GIT). The ends of each caecae were tied off to prevent contamination and to enhance the culturing of anaerobic bacteria. In the laboratory, caecal contents were selectively cultured for Clostridium perfringens, Escherichia coli, Enterococcus faecium, E. faecalis, and vancomycin-resistant enterococci (VRE). Salmonella enterica was isolated using pre-enrichment followed by selective culture. The minimum inhibitory concentration (MIC) micro broth dilution test as prescribed by the Clinical and Laboratory Standards Institute USA (CLSI), previously known as National Committee of Clinical Laboratories (NCCL), was used to determine the susceptibility of the isolates to the following antimicrobials: vancomycin, virginiamycin, doxycycline, trimethoprim, sulphamethoxazole, ampicillin, bacitracin, enrofloxacin, erythromycin, fosfomycin, ceftriaxone and nalidixic acid. The same was done on the faeces of 29 abattoir workers exposed to potentially resistant micro-organisms from broilers and 28 persons used as controls, who had not been equally exposed to potentially resistant micro-organisms from broilers. Both of the human populations had not been treated with antimicrobials within three months prior to sampling. Statistical analysis was done by Fisher’s exact test. No salmonellae and VRE on VRE selective agar (Oxoid UK) were cultured. Two Clostridium perfringens, 168 E. coli, 20 E. faecalis and 96 E. faecium isolates from the broiler caecae were cultured. Fifty four (28 and 26) E. coli, 24 (21 and 3) E. faecalis and 12 (2 and 10) E. faeciumfrom humans were cultured. The figures in brackets represent the abattoir workers and human controls respectively. The majority of E. coli isolates from broilers had MIC’s above the cut off point for the antimicrobials tested. Low resistance was observed among broiler enterococci isolates to vancomycin, virginiamycin, trimethoprim and ampicillin. A comparison of the median MIC’s of isolates from abattoir workers (packers) and the control group revealed significant differences in the median MIC’s for the following antimicrobials; E. faecalis: enrofloxacin (p=0.019). E. faecium, trimethoprim (p=0.01), enrofloxacin (p=0.029) and erythromycin (p=0.03). E. coli: trimethoprim (p=0.012) and ampicillin (p=0.036). Use of antimicrobials as feed additives causes resistance among enteric bacteria from broilers. Significant differences between median MIC’s of abattoir workers (packers) and the control group were observed for therapeutics and not growth enhancers. There was a tendency for isolates from abattoir workers to have a higher median MIC and a higher number of resistant isolates as compared to the control group. In spite of the fact that there was a high level of resistance in the enteric commensal bacteria of broiler caecae, an association could not be shown with that of the human enteric bacteria. It could not be concluded that a significant AMR transfer to poultry abattoir workers existed. This notwithstanding, both the control and experimental group, carried levels of resistance among their enteric bacteria that could be described as being high.