A survey of the antimicrobial susceptibility of Escherichia coli isolated from Sable Island horses.

In this research, a survey was conducted in 2014 to monitor antimicrobial resistance among the wild horses living on Sable Island, off the east coast of Canada. The horses were found to have minimal antimicrobial resistance with around 3% of samples tested showing resistance, most commonly to tetracycline.

Geographical and Biological Context

• The study was carried out on Sable Island, situated approximately 160 km off the east coast of Nova Scotia, Canada.
• The island is home to a unique population of wild horses which are geographically isolated and have no contact with domestic animals, minimal contact with humans, and have never received antimicrobials.
• This isolation makes these horses an ideal population for studying the spread of antimicrobial resistance in nature.

Research Methodology

• As part of an ongoing monitoring program, the researchers collected fecal samples from 508 horses, representing 92% of the total population, between July and September 2014.
• The fecal matter was then selectively cultured for Escherichia coli (E. coli) on two types of media, MacConkey and CHROMagar ESBL.
• The antimicrobial susceptibilities of the E. coli was determined and those resistant to β-lactam antimicrobials were further screened for β-lactamase genes using Polymerase Chain Reaction (PCR).

Findings

• E. coli was found in 146 (28.7%) of the horses tested.
• The majority of isolates (97%) were found to be susceptible to all drugs tested, indicating a low level of antimicrobial resistance.
• The most common form of resistance detected was to the antibiotic tetracycline, found in E. coli isolated from 4 (2.7%) of the horses.
• A single isolate was found to be resistant to three antibiotics: ampicillin, ceftriaxone, and ceftiofur. This isolate possessed the CTX-M-1 gene, indicating antimicrobial resistance.

Conclusion

• The results demonstrate that while antimicrobial resistance is generally uncommon in isolated populations such as the Sable Island horses, clinically relevant resistance genes do exist in the population.
• This finding underlines the ubiquity of antimicrobial resistance and the potential for its spread even in populations that have not been subjected to medical treatments.