Spreading fresh feedlot manure on paddocks to improve fertility could worsen the growing crisis in human antibiotic resistance, new research from the University of New England says.
UNE PhD student Fadhel Abbas, who conducted the study at the university's research feedlot at Tullimba, west of Armidale, assessed 11 types of antibiotics by growing colonies of bacteria harvested from fresh manure.
Mr Abbas exposed the colonies to a standard and then double-dose of each antibiotic and looked at soils treated and not treated with feedlot manure.
He found 30 to 75 per cent of the antibiotic-resistant bacterial load in fresh manure was present in soil treated with fresh manure, depending on the class of antibiotic.
However, levels of antibiotic-resistant bacteria plunged sharply in feedlot manure that was stored for at least five months - likely due to anti-microbial effects like sunlight, high temperatures, acidity, and moisture.
UNE microbiologist Dr Gal Winter said once antibiotic-resistant bacteria are in the soil, they could be transferred to humans via the skin, inhalation, or through plants.
"Living bacteria may not be needed to create new generations of antibiotic-resistant bacteria, only gene fragments of dead bacteria," Dr Winter said.
"Bacteria are very good at integrating DNA from their surrounding into their genome."
UNE biochemistry and immunology senior lecturer Dr Nick Andronicos said the potential for feedlot manure to contribute to human antibiotic resistance was compounded by the use of the same classes of antibiotic for humans and animals.
"If we used different classes of antibiotics in feedlots to those we use in human health, then the growth of antibiotic resistance might be slowed. At the moment, that's not the case," Dr Andronicos said.
"Everyone is aware that there is a problem, but so far we haven't developed effective solutions to break these cycles."
Dr Andronicos said many livelihoods and substantial parts of our food systems depended on intensive livestock production, which in turn depended on a degree of antibiotic use.
"We need to come up with innovative solutions, but do so carefully so we're not short-changing either food production in a crowded world, or human and animal health," he said.
In 2018, Australia's feedlot industry became one of the first in the world to launch formal antimicrobial guidelines.
The guidelines, which were voluntary, became mandatory on January 1, 2022.
Australian Lot Feeders' Association president Barb Madden said very low levels of antimicrobial resistance was derived from cattle feedlots in Australia and the industry was a global leader when it came to stewardship.
"Published industry research has demonstrated very low levels of antimicrobial resistance is derived from cattle feedlots in Australia, however, as a sector we will not become complacent, and we will continue to work with research partners to respond to emerging threats relating to antimicrobial resistance," Ms Madden said.
"Our antimicrobial stewardship standards became a mandatory component of the National Feedlot Accreditation Scheme as of the first of January this year - a significant milestone in our continuous journey for improvement."
Ms Madden said ALFA and the feedlot industry were committed to preserving the efficacy of antimicrobials to ensure the health of cattle was not compromised and to maintain the safety of its product for consumers.
"As the researchers from this recent study have noted, consumers can have full confidence that Australian beef is safe to eat," she said.
In November, Australian Veterinarian Association policy and veterinary science national manager Dr Melanie Latter said antimicrobial resistance was one of the top ten global issues identified as a threat to human health and the veterinary profession was working alongside human health professionals to address the issue.
"Australian veterinarians are trained and experienced in the principles of judicious antimicrobial use, and as a result, Australian animals have low levels of antibiotic resistance in their bacterial fauna, compared to other countries," Dr Latter said.
Last week, the AVA announced the release of antimicrobial prescribing guidelines for dairy cattle.
It said beef cattle and horse antimicrobial prescribing guidelines will follow later this year.
Antimicrobial prescribing guidelines for poultry and sheep were completed in 2020, while pig guidelines were completed in 2019.
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