The evidence points to a pattern of multi-drug resistant R. equi spread and evolution directly determined by antibiotic pressure in equine farms, they said.
They said their study probably underestimates the extent of the spread of the multi-drug resistant form.

The study team said the evidence indicated increasing prevalence of multi-drug resistant R. equi since it was first formally documented in 2002. It is caused by a clone, dubbed R. equi 2287, attributable to changes driven by macrolide/rifampin therapy. The clone likely emerged after large-scale use of the antibiotic combination in the US to prevent the onset of pneumonia in foals.

The authors said their analyses showed that R. equi 2287 has diversified since its first documented isolation. They found resistance to macrolides, lincosamides, streptogramins, and, in a substantial proportion, also to tetracycline.

“All of these antibiotic drugs are listed as critically or highly important for human medicine by the World Health Organization.”

They continued: “Our findings illustrate that overuse of antimicrobial prophylaxis in animals can generate multi-drug resistant pathogens with zoonotic* potential.
“In addition to compromising the therapeutic management of equine R. equi infection, these isolates represent a potential hazard to human health because of the risk of zoonotic transmission.”

*Zoonotic: Zoonotic diseases (also known as zoonoses) are caused by germs that spread between animals and people.

Source: HorseTalk article. Origin study: CDC