Antimicrobial resistance in faecal Escherichia coli isolates from horses treated with antimicrobials: a longitudinal study in hospitalised and non-hospitalised horses.

The study investigates the rise and persistence of drug-resistant E. coli in horses treated with antibiotics. The results indicated that antibiotic treatment in horses, both in hospital and community settings, increased the risk of faecal shedding of drug-resistant E. coli but this is usually temporary.

Objective of the Study

• The primary purpose of this research was to investigate the occurrence and persistence of antibiotic-resistant Escherichia coli, commonly known as E. coli, in the stool of horses treated with antibiotics in both hospital and community settings.

Methodology

• Stool samples were collected from horses either hospitalised or treated outside the hospital and from untreated horses as control.
• Samples were taken before treatment, five days after treatment, and again at two weeks and two months after treatment in treated horses.
• The resistance of the E. coli in the stool samples to 15 different antibiotics was tested through a method called disc diffusion, while additional tests were performed to identify specific antibiotic-resistant genes.

Findings

• Resistance to antibiotics was found in 60.5% of all samples, with no significant difference between those from hospitalised and non-hospitalised horses.
• The likelihood of a sample containing a drug-resistant strain significantly increased five days after treatment in treated horses but not in untreated horses.
• Two weeks after treatment, resistance in non-hospitalised horses returned to pre-treatment levels. In hospital-treated horses, it remained significantly higher than pre-treatment level but returned to baseline two months after treatment.
• In seven samples (17 isolates), production of extended-spectrum beta-lactamases (ESBL), which are enzymes that confer resistance to most beta-lactam antibiotics, was observed. Within these, two specific resistance genes were identified – bla(CTX-M) and bla(TEM).

Implications

• The results of this study indicate that the use of antibiotics in horses increases the risk of the emergence of drug-resistant E. coli, though this effect is usually transient.
• The widespread prevalence of resistant strains suggests a need for measures to minimise potential spread. This could include better antibiotic stewardship and hygiene protocols, especially in hospitals where such resistance can pose a danger to other animals.