Urinary Tract Infections (UTIs) in Dogs and Cats: Insights from a Hong Kong Study on Antimicrobial Resistance

Urinary tract infections (UTIs) are common clinical problems in both dogs and cats, often leading to recurrent cases of cystitis and pyelonephritis. In addition to following antimicrobial treatment guidelines¹, regional epidemiological analysis can offer valuable and specific insights to help veterinarians better understand antimicrobial resistance (AMR) trends and make informed treatment decisions.

In 2023, a retrospective study² on UTIs in companion animals was published in Hong Kong, aiming to evaluate the relationship between clinical antimicrobial usage and bacterial resistance patterns from 2018 to 2020. The study analyzed urine culture data from 15,449 canine and feline samples collected over three years. Of these, 5,731 samples (37%) yielded positive bacterial cultures, with dogs accounting for 55.2% and cats for 44.8% of the positive cases.

However, only 311 isolates (11%) out of the 5,731 culture-positive cases were fully susceptible to all tested antimicrobials, while a concerning 56% exhibited multidrug resistance. This highlights the growing complexity in empirical prescribing and the difficulty in selecting effective treatments against diverse bacterial strains.

The study found that the types of pathogens causing UTIs in dogs and cats were relatively consistent. For dogs, the top five bacterial pathogens were Escherichia coli, Proteus spp., Staphylococcus spp., Enterococcus spp., and Klebsiella spp., collectively accounting for approximately 90% of the annual positive samples. For cats, the dominant pathogens included E. coli, Enterococcus spp., Staphylococcus spp., Pseudomonas spp., Proteus spp., and Klebsiella spp., comprising 95% of the positive cases in the same period.

Of particular concern, these common uropathogens demonstrated widespread resistance to first-line antimicrobial agents such as amoxicillin, ampicillin, and trimethoprim-sulfamethoxazole. For example:

• E. coli: The most frequently isolated pathogen in feline UTI cases, accounting for 45–49% of positive cat samples annually. It also comprised 34–39% of dog isolates. Resistance to amoxicillin and ampicillin reached 47% in cats and 50% in dogs.
• Klebsiella spp.: Exhibited extremely high resistance rates to amoxicillin and ampicillin (>96%) in both species, and moderate resistance (50–60%) to cephalosporins, fluoroquinolones, and penicillins.
• Staphylococcus spp.: Showed resistance rates of 78% to amoxicillin and 60% to ampicillin.
• Enterococcus spp.: Demonstrated over 95% resistance to trimethoprim-sulfamethoxazole. Moreover, as cephalosporins are ineffective against Enterococci, careful selection of alternative antimicrobials becomes critical to avoid accelerating resistance.

Even more alarming, multidrug resistance—defined as resistance to three or more antimicrobial classes—was observed in 56% of positive cultures, with 68% originating from canine samples. Despite these high resistance rates, the three-year data showed that pathogen distribution and resistance trends remained relatively stable throughout the study period.

In conclusion, this study clearly identifies the predominant pathogens associated with UTIs in dogs and cats in Hong Kong, along with their widespread resistance to first-line antimicrobials—especially the high rate of multidrug resistance. These findings serve as an important alert to clinicians when selecting empirical treatments. While the resistance trends remained stable during the study period, veterinarians should continue to monitor local AMR patterns closely. Whenever possible, bacterial culture and sensitivity testing should be encouraged to guide more accurate and effective antimicrobial choices.

The research team also emphasized that promoting judicious antibiotic use, alongside tools such as diagnostic testing systems, could support veterinarians in making more informed therapeutic decisions—ultimately contributing to the effort to curb the spread of antimicrobial resistance.

References:

1. J. Scott Weese et. al., International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats, The Veterinary Journal, 2019. https://doi.org/10.1016/j.tvjl.2019.02.008
2. Olivia S. K. Chan et. al., A Retrospective Study of Antimicrobial Resistant Bacteria Associated with Feline and Canine Urinary Tract Infection in Hong Kong SAR, China—A Case Study on Implication of First-Line Antibiotics Use, Antibiotics, 2022, 11, 1140. https://doi.org/10.3390/antibiotics11091140