Rapid NP test for detection of aztreonam-avibactam resistance in Pseudomonas aeruginosa.

OBJECTIVES

To develop and evaluate a rapid phenotypic method for detecting aztreonam-avibactam (AZA) resistance-associated phenotypes in Pseudomonas aeruginosa.

METHODS

Test isolates were incubated in medium containing fixed concentrations of AZA (aztreonam 20 µg/mL and avibactam 4 µg/mL). Resazurin was used as a redox indicator to monitor bacterial metabolic activity, with colour change from blue to purple/pink indicating growth. The assay was evaluated using 103 clinical P. aeruginosa isolates with different AZA MIC profiles, using broth microdilution as the reference method. Isolates were classified according to the EUCAST tentative ECOFF-based epidemiological framework. Interassay reproducibility was assessed using independent assay runs.

RESULTS

The rapid NP test showed 100% agreement with the tentative ECOFF-based wild-type/nonwild-type classification derived from the reference broth microdilution method across all 103 clinical isolates. Consistent wild-type/nonwild-type classifications were obtained across independent assay runs, supporting the interassay reproducibility of the method. The total turnaround time was 8 h.

CONCLUSIONS

This method is simple, rapid, and reliable, providing an intuitive approach for detecting AZA resistance-associated phenotypes in P. aeruginosa, with potential utility as a targeted screening approach in clinical microbiology laboratories.