Reducing antimicrobial resistance with oregano essential oil

University researchers, Dr Partha Ray and Dr Caroline Rymer, undertook a trial to determine the effect of supplementing Anpario’s Orego-Stim Liquid (a source of 100% natural oregano essential oil), in waste milk fed to dairy calves, on the population of antimicrobial resistant bacteria in their faeces. Holstein male calves were offered either waste milk treated with Orego-Stim Liquid for 10 days or a control diet of the same waste milk source without the addition of Orego-Stim Liquid. After the initial 10 days, all calves were fed the same ration of untreated waste milk and concentrates until weaning.

Oregano essential oil supplementation not only reduced the abundance of cefquinome-resistant E. coli but also delayed the emergence of resistance to cefquinome,” – Dr Partha Ray.

Potential solution

The results of the study were very promising, offering a potential solution in helping to reduce the presence of antimicrobial resistant bacteria. In the faeces of calves fed waste milk with no Orego-Stim, 44.1% of E. coli present were resistant to the cephalosporin antibiotic (cefquinome). However, in calves fed waste milk supplemented with Orego-Stim Liquid until day ten, this was significantly reduced to only 12.6% of total E. coli being resistant to cefquinome.

It was even more promising that resistance to the critically important cefquinome was reduced,” – Dr Caroline Rymer.

“Oregano essential oil supplementation not only reduced the abundance of cefquinome-resistant E. coli but also delayed the emergence of resistance to cefquinome,” says Dr Partha Ray, lecturer in dairy animal science at Reading University. “We are conducting further studies to understand the mechanism underlying the effect of Orego-Stim feeding on antimicrobial resistance in the gut of young cattle. Improving our understanding of the mechanism is the only way we can refine the practice of feeding the essential oil based supplement to make it more sustainable.”

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Feeding supplements which have antimicrobial activity may themselves encourage the development of antimicrobial resistance. It was therefore very pleasing that there was no evidence that feeding Orego-Stim increased the resistance of E. coli to any of the antibiotic classes tested. It was even more promising that resistance to the critically important cefquinome was reduced,” said Dr Caroline Rymer, associate professor of animal science at Reading University.