Farm-Level Impact of Therapeutic Antimicrobial Use on Antimicrobial-Resistant Populations of Escherichia coli Isolates from Pigs

摘要

We investigated the farm-level impact of the use of several different antimicrobial agents on the population ofnantimicrobial-resistant commensal bacteria of animal origin to appropriately assess the release risk of resistance. Thisnstudy was carried out based on the results of a survey on the history of antimicrobial drug use in 297 pig farms andnantimicrobial susceptibility testing for the 545 Escherichia coli isolates (one or two isolates=pig=farm). A comparativenanalysis with the nonexposed herd revealed that ampicillin (ABPC) resistance in E. coli increased in the herds thatnwere exposed to penicillin (relative risk [RR], 1.75) and penicillin–streptomycin (RR, 2.28); dihydrostreptomycinn(DSM) resistance, in the penicillin–streptomycin-exposed herd (RR, 1.75); and trimethoprim (TMP) resistance in thenmethoprim–sulfonamide-exposed herd (RR, 2.10). On the other hand, ABPC and DSM resistances increased in thentetracycline-exposed herd (RR, 1.66 and 1.58, respectively); TMP resistance, in the penicillin-exposed herd (RR, 1.77);nand oxytetracycline and kanamycin resistances, in the penicillin–streptomycin-exposed herd (RR, 1.28 and 2.22,nrespectively). These results demonstrated that the development of cross-resistance and coresistance, imposed by thentherapeutic use of the antimicrobials studied, contributed the farm-level prevalence of antimicrobial-resistant E. colinand that the influence of coselection was characteristic to individual antimicrobial agents used.