Masters Theses

Date of Award

5-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Alan Mathew

Committee Members

Kelly Robbins, David Golden

Abstract

The effects of farm use or exclusion of antibiotics on antibiotic resistance patterns of bacteria were compared using fecal samples from live swine. Four farms that used antibiotics and three farms that excluded antibiotics from production were selected and from each farm, 6 pigs from each of 4 weight groups (4.5, 23, 45, and 109 kg) and 5 sows were randomly selected for collection of fecal samples. E. coli, O157:H7 E. coli, and Salmonella spp. were isolated from fecal samples and tested for sensitivity to gentamicin, sulfamethazine, oxytetracycline, ceftiofur, and ampicillin using a standardized minimum inhibitory concentration (MIC) analysis. Resistance patterns were markedly different between farm types in E. coli, and moderately so in Salmonella. In both cases, isolates from farms that excluded antibiotics had lower (P < 0.05) MICs. The number of resistant isolates and those that demonstrated multiple resistance patterns was greater (P < 0.05) on farms that used antibiotics. E. coli from farms that excluded antibiotics had significantly lower (P < 0.001) MICs for gentamicin, sulfamethazine, oxytetracycline, and ampicillin and lower (P < 0.10) MICs for ceftiofur. Farm type differences were most evident for isolates from younger pigs for gentamicin, ceftiofur, and ampicillin but were also noted among all pig groups for sulfamethazine and oxytetracycline. In Salmonella, the MICs were higher from farms that used antibiotics particularly for oxytetracycline and ceftiofur (P < 0.001). O157:H7 E. coli were isolated from 2 farms, both of which used antibiotics in production, thus a relevant analysis on that bacterium was not possible. In total, these data indicate that exclusion of antibiotics in swine production decreases antibiotic resistance in E. coli, and to a lesser extent resistance in salmonellae.

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