Antimicrobial Resistance in Commensal Escherichia coli Isolated from Pigs and Pork Derived from Farms Either Routinely Using or Not Using In-Feed Antimicrobials.

Chanwit Tribuddharat,Nuvee Prapasarakul,David J. Hampson,Padet Tummaruk,Waree Niyomtham,Kittitat Lugsomya,Jitrapa Yindee

doi:10.1089/mdr.2018.0154

Abstract

The aims of this study were (i) to evaluate whether routine in-feed antimicrobial use in pigs or not resulted in differences in antimicrobial resistance (AMR) E. coli at different pig producing stages, and (ii) to determine whether resistant strains were presented in pig meat postslaughter. A total of 300 commensal E. coli isolates were obtained and examined for antibiograms, AMR genes, plasmid replicons, and molecular types. The isolates were from two farms either using (A) or not using in-feed antimicrobials (NA), sampled four times during the production cycle and once postslaughter. E. coli resistant to aminoglycosides containing aadA1, aadA2, and aadB and extended-spectrum beta-lactamase-producing (ESBLP) E. coli containing blaCTX-M-1 were significantly increased in the nursery and growing periods in farm A compared to farm NA. IncI1-Iγ and IncHI2 were common in the nursery period and were shown to transfer blaCTX-M genes by conjugation. ST10 was the most common type only found in live pigs. ST604, ST877, ST1209, and ST2798 ESBLP were found only in live pigs, whereas ST72, ST302, and ST402 ESBLP were found in pig meat.

Highlights

The ongoing increase in antimicrobial resistance (AMR) in enteric bacteria in production animals and their potential transmission to humans represent a major threat to public health.[1]
Significant differences in resistance rates and extended-spectrum beta-lactamase-producing (ESBLP) phenotype between sampling periods were only found on farm A, and only for a few antimicrobials, with, in each case, the highest rates being in the nursery and grower periods
Even though it is understood that commensal bacteria in animals may act as a reservoir of AMR, to date, evidence verifying a direct link between these organisms in livestock and their occurrence in meat products is limited.[22]

Summary

Introduction

The ongoing increase in antimicrobial resistance (AMR) in enteric bacteria in production animals and their potential transmission to humans represent a major threat to public health.[1] Commensal enteric bacteria such as Escherichia coli (E. coli), which reside for prolonged periods in the intestinal tract, potentially represent an important reservoir of AMR in the food chain, and they make good representative markers for investigating dynamic changes in AMR genes.[2] Even though the source of AMR has not always been identified using molecular epidemiological analysis or DNA-based data, bacteria from livestock are believed to be a major source of AMR in the environment, and resistant bacteria and resistance genes may be acquired by the human gut microbiome.[3].

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Conclusion