Drug resistance among some bacteria that infect horses continues to grow

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Staphylococcus aureus bacteria magnified 20,000 times by a scanning electron microscope, with false color added. This was from a vancomycin resistant culture. Content provider: Centers for Disease Control / Matthew J. Arduino. Photo:: Janice Haney Carr (Public domain) via Wikimedia Commons
Staphylococcus aureus bacteria magnified 20,000 times by a scanning electron microscope, with false color added. This was from a vancomycin resistant culture. Content provider: Centers for Disease Control / Matthew J. Arduino. Photo: Janice Haney Carr (Public domain) via Wikimedia Commons

Scientists in France have found growing drug resistance in some bacteria in horses, charting increases in recent years.

They say their results suggest veterinarians need support to further encourage the proper use of antibiotics.

The emergence and the spread of antimicrobial drug-resistant bacteria around the world is a major public health issue.

In fact, the transmission of these bacteria from animals to humans has been already observed.

“In this context, the close relationships between horses and humans may contribute to cross-infection,” Albertine Léon and her fellow researchers wrote in the journal, Animals.

“Horses are now recognised to be potential reservoirs of antimicrobial resistance, which can be transmitted to other animal and human pathogens.”

For their study, the researchers set out to learn more about the antimicrobial susceptibility profiles of major equine pathogens over four years, from 2016 to 2019.

More than 7800 bacterial isolates collected from horses in France with different types of infection were analysed for their antimicrobial susceptibility.

An increase in the resistance of Staphylococcus aureus and Enterobacter species was observed between 2016 and 2019. The percentage of multi-drug resistant strains rose from 24.5% to 37.4% among S. aureus isolates, and from 26.3% to 51.7% among the Enterobacter samples tested.

“Our results point to the need to support veterinary antimicrobial stewardship to encourage the proper use of antibiotics,” they said.

However, the news wasn’t all bad.

Following the implementation of two French national plans to reduce animal exposure to veterinary antibiotics, the study showed decreases in the resistance among Group C Streptococci against five classes of antibiotics.

Klebsiella pneumoniae showed a decrease in resistance against four classes of drugs, and Escherichia coli showed a decrease against one class.

“However, Staphylococcus aureus, Escherichia coli and Enterobacter species presented an increased resistance against all the tested classes, excepted for two-fifths of E. coli.”

Discussing their findings, the study team said equine pathogens with zoonotic potential — the ability to infect humans — should be carefully taken into account.

“To date, the use of antimicrobials in equine veterinary medicine remains a necessity in many cases because the methods for the prevention of bacterial infections in horses are limited, with few or no vaccines available.

“In this context, antimicrobials are essential to equine health, and this study underlines the importance of performing antimicrobial susceptibility testing in order to optimise antimicrobial therapy in horses and to reduce the occurrence of resistance.”

Such studies, they said, are essential for evaluating the evolution of antimicrobial resistance and its potential threat to public health.

Analysis of the resistance mechanisms displayed by major bacteria is warranted, they say.

“The use of whole-genome sequencing of strains of interest will prove to be invaluable for investigating molecular epidemiology.”

Léon, A.; Castagnet, S.; Maillard, K.; Paillot, R.; Giard, J.-C. Evolution of In Vitro Antimicrobial Susceptibility of Equine Clinical Isolates in France between 2016 and 2019. Animals 2020, 10, 812.

The study, published under a Creative Commons License, can be read here

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