A comparison of antibiotic resistance in bacteria isolated from swine herds in which antibiotics were used or excluded

Alan G. Mathew, MS, PhD; Melissa A. Beckmann, MS; Arnold M. Saxton, MS, PhD

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Objective: To determine the effects on antibiotic resistance patterns of selected bacteria when antibiotics are used or excluded in swine.

Methods: Four herds which had been subjected to antibiotic use (AU) and three herds that had not been subjected to antibiotics (AF) were selected. From each herd, six pigs from each of four weight groups (4.5, 23, 45, and 109 kg) and five sows were randomly selected for collection of fecal samples. Non-hemolytic Escherichia coli and potential foodborne pathogens, including Salmonella spp. and E coli O157:H7, were isolated from fecal samples and tested for susceptibility to ampicillin, ceftiofur, gentamicin, oxytetracycline, and sulfamethazine, using a standardized minimum inhibitory concentration (MIC) analysis.

Results: Susceptibility patterns were different between herd types for E coli, and to a lesser extent for salmonellae. In general, Ecoli isolates from AF herds demonstrated lower MICs for ampicillin, gentamicin, oxytetracycline, and sulfamethazine. The number of resistant isolates was greater from AU herds compared to AF herds. Herd type differences were more evident for isolates from younger pigs for ampicillin, gentamicin, ceftiofur, and sulfamethazine, whereas differences were more pronounced in older pigs and sows for oxytetracycline. For salmonella, MICs for oxytetracycline and ceftiofur were greater for AU herds compared to AF herds.

Implications: Exclusion of antibiotics in swine production decreases, but does not eliminate, antibiotic resistance in E coli. Antibiotic use in swine appears to have a greater effect on resistance patterns of Ecoli than of salmonellae.

Keywords: antibiotics, drug resistance, Escherichia coli, Salmonella

RIS citationCite as: Mathew AG, Beckmann MA, Saxton AM. A comparison of antibiotic resistance in bacteria isolated from swine herds in which antibiotics were used or excluded. J Swine Health Prod 2001;9(3):125-129.

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