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.