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Evaluation of a Rapid, Low-Cost Broth Turbidity Test for Detecting Ampicillin-Resistant Lower Urinary Tract
W Cooper Brookshire1, Larry Ballard1, Anna Collinsgru1
1Mississippi State University College of Veterinary Medicine, Mississippi State, Mississippi, USA.
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.
