Feedlots may contribute to antibiotic resistance, research finds

calendar icon 12 January 2022
clock icon 2 minute read

University of New England (UNE) research has found evidence that antibiotic use in domestic animals may be limiting future human health options. Analysis by UNE PhD student Fadhel Abbas found that farm soils on which feedlot manures had been spread carried significantly higher levels of bacteria resistant to antibiotics compared to untreated soils.

Abbas's research reveals that antibiotic bacteria that have evolved under feedlot conditions readily transfer to farmland soils and could have significant implications for human and animal health.

Abbas's PhD supervisor, UNE microbiologist Gal Winter, said that once antibiotic-resistant bacteria are in the soil, they can 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. “Bacteria are very good at integrating DNA from their surrounding into their genome,” Winter said.

Cattle feedlots routinely use antibiotics to maintain animal health in crowded, often dusty conditions. Manure from feedlots is often collected and spread on agricultural land to improve fertility.

The World Health Organisation (WHO) has said that antibiotic resistance as one of the biggest threats to global health, food security and development.

Abbas examined bacteria-soil interactions at UNE's research feedlot, Tullimba.

He assessed 11 types of antibiotics by growing colonies of bacteria harvested from fresh manure, and soils treated and not treated with feedlot manure, and exposing the colonies to a standard and then double-dose of each antibiotic.

Fresh feedlot manure carried significantly higher populations of antibiotic-resistant bacteria compared to treated and untreated soils and stored manure. Depending on the class of antibiotic, between 30-75% of the antibiotic-resistant bacterial load in fresh manure was present in soil treated with fresh manure.

Another of Abbas's UNE supervisors, Nick Andronicos, a senior lecturer in Biochemistry and Immunology, said the potential for feedlot manure to contribute to human antibiotic resistance is 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," Andronicos said. "At the moment, that's not the case."

Levels of antibiotic-resistant bacteria plunged sharply in feedlot manure that was stored for at least five months. Winter believes this is likely due to anti-microbial effects like sunlight, high temperatures, acidity, and moisture.

UNE animal health researchers work with the global One Health initiative in mind. One Health recognises that the health of people is connected to the health of animals and our shared environment.

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