Antimicrobial resistance in commensal bacteria in bovine faeces at slaughter

Summary

Antimicrobials have been utilised by the Australian cattle industry to prevent infection and treat disease of animals since the 1950s. Although Australia does not have a national, ongoing surveillance program for the monitoring of antimicrobial resistance (AMR) in the animal production sector, periodic assessments are conducted to test for AMR.

This study was conducted to determine the presence of non-wild type (NWT) populations of bacteria, opposed to wild-type (WT), from the faeces of beef cattle, dairy cattle and veal calves at slaughter, which were then assessed for their response to antimicrobials. The presence of NWT bacteria suggests that the bacteria have been in the presence of antibiotics and may potentially become resistant to them.   

Results showed that 94.0% of Salmonella, 83.8% of E. coli and 75.8% of Enterococcus isolates were WT for all antimicrobials tested. This suggests responsible use of antibiotics in cattle production in Australia.

Objectives

The main objective of this project was to collect 1000 faecal isolates from beef cattle, dairy cattle and veal calves and determine the resistance of any Salmonella, E. coli or Enterococcus isolated from the faeces to a range of antimicrobials. The prevalence of non-wild type resistance and multi-antibiotic drug resistance were determined and results compared with a similar survey conducted in 2013.

Key findings

• E.coli was isolated from 969 (96.8%) samples, Salmonella from 184 (18.4%) samples and Enterococcus from 907 (90.6%) samples.
• The study determined that 94.0% of Salmonella, 83.8% of E. coli and 75.8% of Enterococcus isolates were WT for all antimicrobials tested.
• Populations of NWT isolates to antimicrobials that are considered highly or critically important to human medicine were low and there was limited evidence of specific production practices, such as grain-feeding, leading to widespread disproportionate development of NWT isolates.

Benefits to industry

The outcomes of the study permit the Australian beef industry to arrive at the same conclusion as the 2013 study - that is, populations of NWT isolates to antimicrobials considered highly or critically important to human medicine are low. There is also limited evidence that specific production practices, such as grain-feeding, lead to widespread disproportionate development of NWT isolates. This is good news for the red meat industry.

MLA action

• The results of this project will be submitted for publication in a scientific journal.
• An interpretive summary of the results will be provided to industry as input into their antimicrobial stewardship programs and further development of antibiotic prescribing guidelines for Australian cattle.
• The results will be presented and discussed in a number of settings, being used to demonstrate the positive performance of the industry in controlling antimicrobial resistance.

Future research

Periodic surveys, such as this, are probably sufficient to monitor antimicrobial resistance at an industry level and will be repeated as needed. Specific surveys may be required more frequently to monitor the development of resistance to antibiotics of high importance to human health. This is a rapidly developing area of OneHealth (human, animal, environmental) policy, so additional studies may be required to respond to emerging issues.

Related resources

MLA publications

• Antimicrobial stewardship guidelines for the Australian cattle feedlot industry, MLA manual, March 2018
• Antimicrobial resistant bacteria in beef production in Australia, MLA final report, 24 November 2014
• Antimicrobials and the cattle industry, MLA fact sheet, July 2014