Susceptibility of Commensal E. coli Isolated from Conventional, Antibiotic-Free, and Organic Meat Chickens on Farms and at Slaughter toward Antimicrobials with Public Health Relevance.

Laura Musa,Valentina Stefanetti,Chiara Francesca Magistrali,Patrizia Casagrande Proietti,Maria Pia Franciosini,Tana Shtylla Kika,Raffaella Branciari,Valeria Toppi,Francesca Blasi,David Ranucci,Maria Luisa Marenzoni

doi:10.3390/antibiotics10111321

Abstract

The spread of resistant bacteria from livestock to the food industry promoted an increase of alternative poultry production systems, such as organic and antibiotic-free ones, based on the lack of antimicrobial use, except in cases in which welfare is compromised. We aimed to investigate the antibiotic susceptibility of commensal Escherichia coli isolated from organic, antibiotic-free, and conventional broiler farms and slaughterhouses toward several antimicrobials critically important for human health. To assess antimicrobial susceptibility, all E. coli isolates and extended spectrum beta-lactamase (ESBL) E. coli were analysed by the microdilution method. The prevalence of tigecycline, azithromycin and gentamicin E. coli-resistant strains was highest in organic samplings. Conversely, the lowest prevalence of resistant E. coli strains was observed for cefotaxime, ceftazidime and ciprofloxacin in organic systems, representing a significant protective factor compared to conventional systems. All E. coli strains were colistin-susceptible. Contamination of the external environment by drug-resistant bacteria could play a role in the presence of resistant strains detected in organic systems. Of interest is the highest prevalence of cephalosporin resistance of E. coli in conventional samplings, since they are not permitted in poultry. Our results suggest that monitoring of antibiotic resistance of the production chain may be helpful to detect “risks” inherent to different rearing systems.

Highlights

Over the years, the rapidly increasing demand for livestock products by the human population has led to the development of intensive production of food animals, such as cattle, poultry and pigs [1], and the increase of antimicrobial resistance, due to the uncontrolled use of antimicrobials [2,3] for the prevention and treatment of infections, promotion of growth and improvement in production [4].waste from hospitals and livestock producers containing antimicrobial residues have facilitated the selection of resistomes in the environment with potential diffusion to animals and humans [5]
We aimed to investigate the antibiotic susceptibility of commensal E. coli, especially towards antimicrobials used in human therapy, isolated in organic, antibiotic-free and conventional (C) broilers on farms and at slaughter
With respect to antimicrobial susceptibility, O and AF samplings showed higher prevalence of E. coli-resistant strains to tigecycline than C (29.3% in O, 20.7% in AF, and 10.3% in C) (Figure 1) with an odds ratio (OR) of 3.59 (p = 0.01) for O (Table 1)

Summary

Introduction

The rapidly increasing demand for livestock products by the human population has led to the development of intensive production of food animals, such as cattle, poultry and pigs [1], and the increase of antimicrobial resistance, due to the uncontrolled use of antimicrobials [2,3] for the prevention and treatment of infections, promotion of growth and improvement in production [4].waste from hospitals and livestock producers containing antimicrobial residues have facilitated the selection of resistomes in the environment with potential diffusion to animals and humans [5]. The diffusion of ESBL could result in unsuccessful therapeutic treatment in human infections and require the use of “last resort antibiotics” (e.g., carbapenems) causing an increased resistance to these antibiotic classes [27,28]. In this scenario, poultry producers have turned to alternative production systems, such as organic (O) and antibiotic-free (AF) farming, based on the lack of antimicrobial use, unless animal welfare is at risk [29].

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