Characterisation of bacterial growth and antimicrobial susceptibility patterns in canine urinary tract infections.

Background: Bacterial urinary tract infection (UTI) is a common reason for antimicrobial therapy in dogs. A reported increase in multi-drug resistance in canine bacterial pathogens, including resistance to extended-spectrum cephalosporins (ESC) is of concern as antimicrobial resistance complicates therapy in dogs. In addition, it is a possible public health concern. The objectives of this study were to investigate the relative prevalence of pathogens in urine samples from dogs with urinary tract infection sampled at referral hospitals, clinics and mixed veterinary practices and to investigate if this was influenced by sample material or by contamination of the culture. The second objective was to assess the susceptibility patterns to clinically relevant antimicrobials and to investigate if this was influenced by whether the samples originated from smaller clinics or from referral hospitals and to perform active screening for the presence of Enterobacteriaceae resistant to ESC.

Results: Escherichia coli was the most frequently isolated pathogen (68%) followed by staphylococci (11%). E. coli isolates were found significantly more often in pure culture than in contaminated samples. Staphylococcus pseudintermedius and Staphylococcus aureus isolates were significantly more prevalent in pre-incubated samples compared to samples submitted as non-incubated media. Susceptibility to the majority of the tested first-line antimicrobials was common. Multiresistance was rare, and these isolates were all susceptible to at least one relevant antimicrobial. Isolates in samples from small animal clinics or mixed veterinary practices were less likely to be susceptible compared to isolates originating from referral animal hospitals. ESC-resistant Enterobacteriacae isolates were found in one per cent of the positive cultures. Bacteria with transferable ESC resistance were confirmed in one dog. The gene demonstrated was bla CMY2.

Conclusions: Choice of sample material might influence the possibility of detecting Staphylococcus pseudintermedius and Staphylococcus aureus isolates in clinical cases of UTI in dogs. Based on the study results, use of first-line antimicrobials is a rational empirical antimicrobial therapy for the studied dog population. E. coli was the most prevalent pathogen, but prevalence of infection with ESC resistant Enterobacteriaceae including E. coli was low, as such isolates were found in only one per cent of the positive cultures.