Full Validation of Pooled Antibiotic Susceptibility Testing Using CLSI Methods and Performance Criteria in UTI...

Background: Here, we validate a unique and rapid susceptibility assay, Pooled Antibiotic Susceptibility Testing (P-AST), used for complicated, persistent, and recurrent urinary tract infections (UTIs), following Clinical and Laboratory Standards Institute (CLSI) protocols and performance metrics. Methods: P-AST™ was validated against the standard disk diffusion method with discrepancy resolution by the broth microdilution reference method. Performance was evaluated for five groups of non-fastidious uropathogenic organisms (Enterobacterales, Enterococci, Staphylococci, Pseudomonas aeruginosa, and Acinetobacter species) for up to 20 antibiotics, as clinically relevant per group. Fresh (144 monomicrobial and 49 polymicrobial) and frozen (78 monomicrobial and 7 polymicrobial) clinical urine specimens, as well as contrived specimens from pre-characterized frozen "challenge" isolates (52 monomicrobial and 37 polymicrobial), were included. Results: P-AST met CLSI target performance criteria of ≥90.0% categorical agreement, <3.0% very major error, <3.0% major error, minor error ≤ 10.0%, or within laboratory standards, and precision > 95.0% across all analysis groups. Across all monomicrobial analyses, there were no very major errors (VMEs), and two major errors (MEs). Across all polymicrobial analyses, there were three VMEs and two MEs. No organism-antibiotic pair analysis had more than a single VME or ME. Conclusions: P-AST, a component of the Guidance^® UTI assay, demonstrates acceptable performance within the thresholds established by CLSI when compared against standard and reference methods for antibiotic susceptibility testing. Appropriate performance was established in both monomicrobial and polymicrobial specimens for five CLSI-defined groups of uropathogenic bacteria, against up to 20 antibiotics as clinically relevant to each organism group.