BACKGROUND : Antimicrobial resistant Staphylococcus are becoming increasingly important in horses because of the
zoonotic nature of the pathogens and the associated risks to caregivers and owners. Knowledge of the burden and
their antimicrobial resistance patterns are important to inform control strategies. This study is an exploratory descriptive
investigation of the burden and antimicrobial drug resistance patterns of Staphylococcus isolates from horses presented
at a veterinary teaching hospital in South Africa.
METHODS : Retrospective laboratory clinical records of 1027 horses presented at the University of Pretoria veterinary
teaching hospital between 2007 and 2012 were included in the study. Crude and factor-specific percentages of
Staphylococcus positive samples, antimicrobial resistant (AMR) and multidrug resistant (MDR) isolates were computed
and compared across Staphylococcus spp., geographic locations, seasons, years, breed and sex using Chi-square and
Fisher’s exact tests.
RESULTS : Of the 1027 processed clinical samples, 12.0% were Staphylococcus positive. The majority of the isolates were
S. aureus (41.5%) followed by S. pseudintermedius (14.6%). Fifty-two percent of the Staphylococcus positive isolates were
AMR while 28.5% were MDR. Significant (p < 0.05) differences in the percentage of samples with isolates that were AMR
or MDR was observed across seasons, horse breeds and Staphylococcus spp. Summer season had the highest (64.3%) and
autumn the lowest (29.6%) percentages of AMR isolates. Highest percentage of AMR samples were observed among the
Boerperds (85.7%) followed by the American saddler (75%) and the European warm blood (73.9%). Significantly (p < 0.001)
more S. aureus isolates (72.5%) were AMR than S. pseudintermedius isolates (38.9%). Similarly, significantly (p < 0.001) more S.
aureus (52.9%) exhibited MDR than S. pseudintermedius (16.7%). The highest levels of AMR were towards β-lactams (84.5%)
followed by trimethoprim/sulfamethoxazole (folate pathway inhibitors) (60.9%) while the lowest levels of resistance were
towards amikacin (14.%).
CONCLUSIONS : This exploratory study provides useful information to guide future studies that will be critical for guiding
treatment decisions and control efforts. There is a need to implement appropriate infection control, and judicious use of
antimicrobials to arrest development of antimicrobial resistance. A better understanding of the status of the problem is a
first step towards that goal.