Rapid detection of imipenem/relebactam susceptibility/resistance in Pseudomonas aeruginosa.

Objectives: Imipenem-relebactam (IPR) has been reported to exhibit a good activity against non-metallo-ß-lactamase carbapenem-resistant Pseudomonas aeruginosa (CRPA), and the rapid detection of susceptibility/resistance to this new therapeutic alternative may be crucial. Therefore, the Rapid IPR Pseudomonas NP test was developed to quickly identify IPR susceptibility/resistance among multidrug-resistant P. aeruginosa.

Methods: The principle of the Rapid IPR Pseudomonas NP test is based on visually detecting glucose metabolization by observing (or not) a color change from yellow to red or orange of the red phenol pH indicator in the presence of imipenem at 2 mg/L and relebactam at 4 mg/L A total of 80 clinical Pseudomonas aeruginosa isolates were analyzed, among which 42 isolates were IPR resistant according to EUCAST guidelines (MICs, susceptible ≤2 mg/L, resistant >2 mg/L). Results obtained with the Rapid IPR Pseudomonas NP test were compared with the reference broth microdilution (BMD).

Results: The sensitivity, specificity and accuracy of the test were found to be 100 %, 89.5 % and 95 %, respectively, using the BMD reference method as a comparator. Moreover, five out of the IPR-susceptible isolates (n = 38) exhibiting an MIC of IPR close to the breakpoint (MIC = 1 mg/L, n = 2; MIC = 2 mg/L, n = 3) yielded to a major error result, namely a positive result with the rapid IPR Pseudomonas NP test (resistance). By contrast, all IPR-resistant isolates (n = 42) were all correctly categorized.

Conclusions: The Rapid IPR Pseudomonas NP test is sensitive, specific, and easy to perform and interpret. Therefore, it is suitable for implementation in routine clinical laboratories.