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The 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. coli in a pig farm during the rearing period. This collaborative study was carried out by researchers of CReSA (IRTA-UAB), Universidad Complutense de Madrid and Universitat de Lleida (Spain).
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. 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 CR E. coli, which was statistically significant in the treated groups. Resistance diminished after treatment. A total of 47 CR E. coli isolates were recovered during the study period; of these, 15 contained blaCTX-M-1, 10 contained blaCTX-M-14, 4 contained blaCTX-M-9, 2 contained blaCTX-M-15, and 5 contained blaSHV-12. The treatment with ceftiofur and amoxicillin was associated with the emergence of CR E. coli during the course of the treatment. However, by the time of finishing, CR E. coli bacteria were not recovered from the animals.
Additionally, results from this study have shown the coexistence of many different CR genes within one farm. The experiments revealed the presence of a great variety of plasmids of many different sizes harboring the same resistance genes. Co-selection by plasmids bearing resistance genes for different antimicrobial families probably plays an important role in the maintenance of resistance mechanisms.
Further studies should be designed to identify other risk factors associated with the persistence of resistance determinants to minimize the recirculation of isolates and/or plasmids within farms.
Impact of the use of ß-lactam antimicrobials on the emergence of Escherichia coli isolates resistant to cephalosporins under standard pig-rearing conditions. Cameron-Veas K, Solà-Ginés M, Moreno MA, Fraile L, Migura-Garcia L. Appl Environ Microbiol. 2015 Mar;81(5):1782-7.