Evaluation of a Rapid, Low-Cost Broth Turbidity Test for Detecting Ampicillin-Resistant Lower Urinary Tract Infections in Dogs and Cats

Background

Effective treatment of urinary tract infections (UTIs) in dogs and cats relies on timely recognition of antimicrobial resistance, but traditional microbiological culture and susceptibility testing require 48–72 h and can be cost-prohibitive.

Objective

To evaluate a novel, low-cost broth turbidity test for detecting ampicillin-resistant UTIs in dogs and cats compared to the gold standard microbiological methods.

Animals

One hundred sixty urine samples from 145 dogs and 15 cats at the Mississippi State University College of Veterinary Medicine.

Methods

From September 2023 to February 2024, urine samples were tested using an ampicillin-supplemented Mueller–Hinton broth turbidity test and gold standard culture with Sensititre MIC plates. Sensitivity, specificity, Cohen's κ, and McNemar's test were calculated.

Results

The broth turbidity test showed 89.47% sensitivity (95% CI: 66.86%–98.72%) and 100% specificity (95% CI: 97.42%–100%) for the detection of ampicillin-resistant organisms in the urine, with substantial agreement (κ = 0.94, p < 0.001) and no classification difference (p = 0.500). Notably, all 36 samples with ampicillin-susceptible organisms identified by the gold standard cultures test were correctly identified as negative for ampicillin resistance by the broth turbidity test.

Conclusions

The broth turbidity test's simplicity and affordability make it a promising tool for in-house use by veterinary practitioners to guide first-line therapy decisions, though its sensitivity could be limited in cases with low bacterial loads or confounding factors such as recent antibiotic administration.