Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015.

The research article presented is a thorough exploration of the prevalence of antibiotic resistance in bacteria found in New Zealand’s equine population, with a focus on those causing respiratory disease in young horses. The research revealed that multi-drug resistance is present and that a careful selection of antimicrobials is necessary to treat bacterial infections.

Introduction and Objectives

• The study was conducted in response to concerns about the declining effectiveness of veterinary drugs and the rising occurrence of multi-drug resistance (MDR) in bacteria affecting New Zealand’s horse population.
• Particular attention was given to stud farms where antibiotics are frequently used to treat respiratory disease without veterinary oversight.
• The aim of the investigation was to analyse the bacterial culture and antimicrobial sensitivity from respiratory samples taken from young horses, specifically those aged between 4 weeks and 3 years old.

Methodology

• A retrospective study of clinical pathology records was carried out, encompassing the period of April 2004 to July 2014.
• The results from the in vitro sensitivity testing by the Kirby-Bauer disk diffusion method were tabulated for the main bacterial species isolated.
• Multiple correspondence analysis was utilised to describe any clustering of multi-drug resistance and selected demographic variables.

Results

• Of the 289 eligible respiratory samples, 237 had at least one aerobic bacterial isolate. The majority (68%) of the 774 bacterial isolates were Gram-positive.
• Streptococcus was identified as the most common genus isolated, accounting for 40% of all isolates.
• Streptococcus’s sensitivity to penicillin, gentamicin, and ceftiofur was over 85%, but it showed only 53% sensitivity to trimethoprim-sulfamethoxone. Sensitivity for Gram-negative bacteria to ceftiofur, tetracycline, and trimethoprim-sulfamethoxone was below 75%.
• Multi-drug resistance was identified in 16% of isolates, affecting 39% of horses.

Conclusion and Recommendations

• This research suggests penicillin as the ideal first-line antimicrobial treatment for most young New Zealand horses suspected of having bacterial respiratory infections.
• Nonetheless, due to the observed incidents of multi-drug resistance, the researchers recommend submitting samples for culture and sensitivity monitoring as a tool to inform antimicrobial selection effectively.
• This study was backed by Massey University McGeorge Fund and the New Zealand Equine Research Foundation.