Pooled Antibiotic Susceptibility Testing for Polymicrobial UTI Performs Within CLSI Validation Standards.

Area of Science:

• Clinical microbiology
• Diagnostic assay development
• Antimicrobial resistance

Background:

• Urinary tract infections (UTIs) present a growing challenge due to increasing antimicrobial resistance.
• Novel diagnostic tests are emerging to overcome limitations of standard urine culture.
• Validation of new tests against established antibiotic susceptibility testing (AST) methods is crucial.

Purpose of the Study:

• To validate a novel diagnostic test, Pooled Antibiotic Susceptibility Testing (P-AST), against standard AST methods.
• To assess the agreement and error rates of P-AST in polymicrobial UTI specimens.
• To evaluate the impact of organism load on antibiotic sensitivity results.

Main Methods:

• Polymicrobial urine specimens were tested using P-AST and standard broth microdilution/disk diffusion (BMD/DD) methods.
• Performance characteristics including essential agreement (EA%), very major errors (VMEs), and major errors (MEs) were evaluated against Clinical and Laboratory Standards Institute (CLSI) guidelines.
• Heteroresistance and the association between organism counts and antibiotic sensitivity were assessed.

Main Results:

• P-AST demonstrated essential agreement ≥90% and met CLSI guidelines for VMEs (<2.0%) and MEs (<3.0%) compared to standard AST.
• When accounting for heteroresistance, VMEs and MEs were both <1.5%.
• Increasing organism counts significantly reduced the number of "sensitive" antibiotics detected per sample.

Conclusions:

• P-AST, as part of the Guidance® UTI assay, performs within CLSI standards for AST in polymicrobial UTI diagnostic specimens.
• The findings support the utility of P-AST for accurate UTI diagnostics.
• The study highlights the importance of considering organism load in interpreting AST results.