UK oregano oil study shows promising results tackling E. coli

Adding an oregano essential oil to calf diets can significantly reduce levels of E. coli bacteria that are resistant to a fourth-generation cephalosporin antibiotic, according to a UK university study.

The University of Reading study saw Holstein male calves were offered either waste milk treated with Orego-Stim Liquid (a source of natural oregano essential oil) for 10 days.

University researchers Dr. Partha Ray and Dr. Caroline Rymer then investigated the effect of supplementing Anpario’s Orego-Stim Liquid on the population of antimicrobial-resistant bacteria in their faeces compared with calves fed 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.


Researchers say 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 oregano oil, 44.1% of E. coli present were resistant to the cephalosporin antibiotic (cefquinome).

However, in calves fed waste milk with the supplement added until day 10, this was significantly reduced to only 12.6% of total E. coli being resistant to cefquinome.

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

These antibiotics are commonly used in human and animal medicine and are classified as ‘highest priority critically important’, therefore safeguarding their use is an absolute necessity.

“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.