Changes in the patterns of antimicrobial resistance of equine pathogens over a fourteen year period

Bacterial resistance to antimicrobials has become a global issue which is affecting veterinary treatment of animals, welfare of animals and can have economic implications. The use of antibiotics in animals can lead to selection of resistance genes that can cause serious risk to human health due to a lack of ability to treat infections. The aim of this project was to investigate the suscepitibility patterns of equine pathogens against a range of antibiotics over a fourteen year period using minimum inhibitory concentrations (MIC‟s) as a measure of resistance. The epsilometer test is an agar diffusion method used to establish if a strain of bacterium is susceptible to the action of a specific antibiotic. It is a predefined, stable gradient with concentrations ranging from 0.001 to 250ug/ul. A total of 2,100 individual MIC tests were carried out. All samples were of equine origin and isolated from clinical cases. The bacteria examined were Escherichia coli, Staphylococcus aureus, Streptococcus equi subsp. equi, Pseudomonas aeruginosa and Klebsiella pneumoniae, which are the most common pathogens of horses. The panel of antibiotics used included; Gentamicin, Ampicillin, Amikacin, Enrofloxacin, Tetracycline, Penicillin and a combination of Trimethoprim/Sulphonimide. The main findings of this study demonstrated a trend in the increase of MIC values for the bacteria Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Streptococcus equi subsp. equi across all antimicrobials tested, with the exception of Staphylococcus aureus where a decreased trend in MIC values was observed. Whilst a decrease in MIC values is a positive finding it must also be noted that clinical resistance levels in Staphylococcus aureus for the majority of antimicrobials tested remained high. Consequently, it is clear from this study that drastic action is needed in the fight against antimicrobial resistance.