Impact of the Use of β-Lactam Antimicrobials on the Emergence of Escherichia coli Isolates Resistant to Cephalosporins under Standard Pig-Rearing Conditions

Abstract

ABSTRACTThe aim of this study was to evaluate if the treatments with ceftiofur and amoxicillin are risk factors for the emergence of cephalosporin resistant (CR)E. coliin a pig farm during the rearing period. One hundred 7-day-old piglets were divided into two groups, a control (n= 50) group and a group parenterally treated with ceftiofur (n= 50). During the fattening period, both groups were subdivided in two. A second treatment with amoxicillin was administered in feed to two of the four groups, as follows: group 1 (untreated,n= 20), group 2 (treated with amoxicillin,n= 26), group 3 (treated with ceftiofur,n= 20), and group 4 (treated with ceftiofur and amoxicillin,n= 26). During treatment with ceftiofur, fecal samples were collected before treatment (day 0) and at days 2, 7, 14, 21, and 42 posttreatment, whereas with amoxicillin, the sampling was extended 73 days posttreatment. CRE. colibacteria were selected on MacConkey agar with ceftriaxone (1 mg/liter). Pulsed-field gel electrophoresis (PFGE), MICs of 14 antimicrobials, the presence of cephalosporin resistance genes, and replicon typing of plasmids were analyzed. Both treatments generated an increase in the prevalence of CRE. coli, which was statistically significant in the treated groups. Resistance diminished after treatment. A total of 47 CRE. coliisolates were recovered during the study period; of these, 15 containedblaCTX-M-1, 10 containedblaCTX-M-14, 4 containedblaCTX-M-9, 2 containedblaCTX-M-15, and 5 containedblaSHV-12. The treatment with ceftiofur and amoxicillin was associated with the emergence of CRE. coliduring the course of the treatment. However, by the time of finishing, CRE. colibacteria were not recovered from the animals.