Urinary tract infections (UTIs) are commonly treated with empirically selected antimicrobials in veterinary practice. Antimicrobial use guidelines recommend administration of amoxicillin or trimethoprim-sulfonamide (TMS) for 3 to 5 days for UTIs, but the efficacy of these recommendations against urinary tract pathogens found in Australian cats and dogs has not been examined.
We analysed bacterial identification and antimicrobial susceptibility results from bacterial isolates from 5614 cat and dog urine samples between 2015 and 2019, predominantly from first opinion veterinary clinics (78%). E. coli was the most prevalent species, and was isolated from 67% of dog and 55% of cat samples. Enterococcus faecalis, Staphylococcus pseudintermedius, Proteus spp., Enterobacter spp., coagulase-negative staphylococci, and Streptococcus canis were also detected commonly. There was relatively little acquired antimicrobial resistance in these isolates, with the exception of a high prevalence of fluoroquinolone resistance in Enterococcus faecalis and Streptococcus canis. Multi-drug resistance was most common in E. coli (9.7%), primarily due to resistance to multiple (non-potentiated) beta-lactam antibiotics, but 84% of these were susceptible to amoxicillin-clavulanate. Using a formula for rational antimicrobial therapy, the most effective empirical antibiotic choice was amoxicillin-clavulanate. However, when isolates were classified based on morphology, amoxicillin was almost as effective as amoxicillin-clavulanate against cocci, and TMS was almost as effective against bacilli, highlighting the value of in-clinic urinary microscopy in selecting empirical therapy, particularly when attempting to improve antimicrobial stewardship in veterinary practice. A novel population analysis was used to combine antimicrobial importance ratings with susceptibility results; findings suggested that when the morphology had not been determined, TMS was the best first-line empirical choice and amoxicillin the best second-line choice.
This study showed favourable antimicrobial susceptibility profiles in dog and cat urinary isolates compared with local human urinary isolates1 and confirmed the current international2 and Australian3 guideline recommendations of TMS or amoxicillin for empirical treatment of sporadic UTIs in dogs and cats.