Efficacy of the modified carbapenem inactivation method (mCIM) for detecting carbapenemase-producing Pseudomonas aeruginosa in a 1,000-bed tertiary hospital in Thailand

Background: Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a prominent healthcare-associated pathogen with worldwide implications for public health. Distinguishing between carbapenemase-producing and noncarbapenemase-producing strains over an extended hospitalization period is vital in assessing the risk of treatment failure in infected patients. Objectives: To study the prevalence of carbapenemase genes and to evaluate the efficacy of the modified carbapenem inactivation method (mCIM) for detecting carbapenemase production among CRPA isolated from Thailand. Materials and methods: A total of 164 CRPA isolates were phenotypically tested for carbapenemase production by the mCIM comparing with genotypic detection of carbapenemase genes using the direct flow chip kits and conventional PCR. In addition, carbapenemase genes were identified by sequencing. Results: The carbapenemase genes, including blaIMP, blaVIM, blaNDM, blaGES, and blaSIM, were found in 83 (50.61%) isolates. The blaIMP showed to be the most prevalent gene, followed by blaVIM and blaNDM, respectively. Of these isolates, 68/83 (82%) of carbapenemase gene-positive isolates were positive by the mCIM assay. The 15 mCIM-negative isolates, six (40%) carried blaVIM-2 gene, while five (33%) isolates contained blaGES-5. Moreover, blaIMP was detected in 3 isolates (20%) and one isolate (7%) of a combination between blaVIM and blaIMP genes. Furthermore, we noted that isolates carrying blaVIM-2 were the most common among the mCIM-negative carbapenemase-producing P. aeruginosa (CPPA), followed by blaGES-5. Conclusion: This study represents a critical report on using mCIM to detect CPPA. It highlights that relying solely on mCIM may not be sufficient for the comprehensive detection of CPPA. Further approaches are needed to enhance the accuracy of detection in this context.