Investigation of EDTA-CarbaNP-direct test for the detection of metallo-β-lactamases in Pseudomonas aeruginosa.

Background: WHO has included carbapenem-resistant Pseudomonas aeruginosa (CR-Pa) in the high priority pathogens list. Ceftazidime-avibactam (CZA) is one of the limited treatment options in CR-Pa infections. Early detection of metallo-β-lactamases (MBL) is important because CZA is not effective against MBL-producing isolates.

Aim: To modify the CarbaNP-direct test (CNPdt) with EDTA and evaluate its use in MBL detection and prediction of CZA resistance CR-Pa isolates.

Methods: 398 CR-Pa isolates from five centres in Türkiye were included. Susceptibility tests were done using EUCAST criteria. The isolates were tested for bla, bla, bla, bla, bla and bla genes using Biospeedy Carbapenem-Resistance qPCR kit and GES Antibiotic-Resistance kit (Bioeksen, Türkiye). We modified CNPdt described by Pasteran et al. by adding a third tube with ethylenediaminetetraacetic acid (EDTA). The isolates with carbapenemase genes were subjected to CNPdt and EDTA-CNPdt. EDTA-CNPdt was considered positive if the tube without EDTA turned yellow while the tube with EDTA remained red and negative if both tubes turned yellow (Fig. 1).

Results: Carbapenemase genes were detected in 55 (13.8 %) of the isolates. CNPdt was positive in 31 of the isolates. Of the 31 isolates, 23 were positive for EDTA-CNPdt. All of these 23 isolates were MBL producers and resistant to CZA. PCR, CNPdt, EDTA-CNPdt and CZA susceptibility test results are shown in Table 2.

Conclusion: The positivity of CNPdt in CR-Pa is limited, but EDTA-CNPdt detected 100 % of MBL-producing isolates when CNPdt was positive. This test can be used for MBL detection and prediction of CZA resistance in CNPdt positive isolates.