Escherichia coli and Salmonella spp. isolated from Australian meat chickens remain susceptible to critically important antimicrobial agents

PLoS One. 2019 Oct 23;14(10):e0224281. doi: 10.1371/journal.pone.0224281. eCollection 2019.

Abstract

The World Health Organisation has defined "highest priority critically important antimicrobials" (CIAs) as those requiring the greatest control during food production. Evidence demonstrating that restricted antimicrobial usage prevents the emergence of resistance to CIA's amongst pathogenic and commensal organisms on a production system-wide scale would strengthen international efforts to control antimicrobial resistance (AMR). Therefore, in a designed survey of all major chicken-meat producers in Australia, we investigated the phenotypic AMR of E. coli (n = 206) and Salmonella (n = 53) from caecal samples of chickens at slaughter (n = 200). A large proportion of E. coli isolates (63.1%) were susceptible to all tested antimicrobials. With regards to CIA resistance, only two E.coli isolates demonstrated resistance to fluoroquinolones, attributed to mutations in the quinolone resistance-determining regions of gyrA. Antimicrobial resistance was observed for trimethoprim/sulfamethoxazole (8.7%), streptomycin (9.7%), ampicillin (14.1%), tetracycline (19.4%) and cefoxitin (0.5%). All Salmonella isolates were susceptible to ceftiofur, chloramphenicol, ciprofloxacin, colistin, florfenicol, gentamicin and tetracycline. A low frequency of Salmonella isolates exhibited resistance to streptomycin (1.9%), ampicillin (3.8%), and cefoxitin (11.3%). AMR was only observed among Salmonella Sofia serovars. None of the Salmonella isolates exhibited a multi-class-resistant phenotype. Whole genome sequencing did not identify any known resistance mechanisms for the Salmonella isolates demonstrating resistance to cefoxitin. The results provide strong evidence that resistance to highest priority CIA's is absent in commensal E. coli and Salmonella isolated from Australian meat chickens, and demonstrates low levels of resistance to compounds with less critical ratings such as cefoxitin, trimethoprim/sulfamethoxazole, and tetracycline. Apart from regulated exclusion of CIAs from most aspects of livestock production, vaccination against key bacterial pathogens and stringent biosecurity are likely to have contributed to the favorable AMR status of the Australian chicken meat industry. Nevertheless, industry and government need to proactively monitor AMR and antimicrobial stewardship practices to ensure the long-term protection of both animal and human health.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • Australia
  • Chickens / microbiology
  • Drug Resistance, Bacterial
  • Escherichia coli / drug effects*
  • Escherichia coli / genetics
  • Escherichia coli / isolation & purification*
  • Food Microbiology
  • Meat / microbiology*
  • Salmonella / drug effects*
  • Salmonella / genetics
  • Salmonella / isolation & purification*
  • Whole Genome Sequencing

Substances

  • Anti-Bacterial Agents

Grants and funding

SA, MOD, KH, AP, DT, DJ - Received Funding From the Australian Government’s Department of Agriculture and Water Resources’ Animal Biosecurity and Response Reform Program (IRMA 17250). The funder (Australian Government’s Department of Agriculture and Water Resources) had an influence on study design in a quality-control context. This consisted of interaction with researchers to ensure the scientific validity of the proposed work plan by comparison with standards established by the OIE and major antimicrobial resistance surveillance programs. The funder was not involved in data collection, analysis, decision to publish or preparation of the manuscript. Additionally, the Australian Chicken Meat Federation provided support for the study in the form of a salary for KH. The Birling Avian Labs provided support in the form of salaries for AP and TH. The specific roles of these authors are articulated in the ‘author contributions’ section.