Antimicrobial Susceptibilities of Aerobic Isolates from Respiratory Samples of Young New Zealand Horses.

Background Decreased efficacy of antimicrobials and increased prevalence of multidrug resistance ( MDR) is of concern worldwide. Objectives To describe and analyze bacterial culture and antimicrobial susceptibilities from respiratory samples submitted from young horses (4 weeks to 3 years old). Animals Samples from 289 horses were submitted to a commercial laboratory. Methods A retrospective database search of submissions made to a New Zealand veterinary laboratory between April 2004 and July 2014. The results of in vitro susceptibility testing by Kirby-Bauer disc diffusion were described and tabulated for the major bacterial species isolated. Multiple correspondence analysis ( MCA) was used to describe the clustering of MDR isolates and selected demographic variables. Results Overall, 774 bacterial isolates were cultured from 237 horses, the majority of these isolates were gram-positive (67.6%; 95% CI 64.3-70.9%). Streptococcus spp. were the most common genus of bacteria isolated and were 40.1% (95% CI 36.6-43.5%) of the isolates cultured. Susceptibility of Streptococcus spp. to penicillin, gentamicin, and ceftiofur was >85%. Overall, gram-negative susceptibility to ceftiofur, tetracycline, and TMPS was <75%. MDR was defined as resistance to 3 or more antimicrobials, and was found in 39.2% of horses (93/237; 95% CI 33.0-45.5%). Conclusions and clinical importance Culture and susceptibility results have highlighted that MDR is an emerging problem for young horses in New Zealand (NZ), where a bacterial respiratory infection is suspected. This should be considered when prescribing antimicrobials, and emphasizes the need for submission of samples for culture and susceptibility. [ABSTRACT FROM AUTHOR]