Comparison of three colloidal gold immunoassays and GeneXpert Carba-R for the detection of variants.

The increasing use of ceftazidime-avibactam has led to the emergence of a wide range of ceftazidime-avibactam-resistant variants. Particularly, the conventional carbapenemase phenotypic assay exhibited a high false-negative rate for KPC-2 variants. In this study, three colloidal gold immunoassays, including the Gold Mountainriver CGI test, Dynamiker CGI test and NG-Test CARBA5, and GeneXpert Carba-R, were used to detect the presence of KPC-2 carbapenemase and its various variants in 42 strains. These strains covered (13/42) and 16 other variants including (1/42), (1/42), (1/42), (6/42), (1/42), (1/42), (1/42), (8/42), (1/42), (1/42), (1/42), (1/42), (1/42), (1/42), (2/42), and (1/42). For KPC-2 strains, all four assays showed 100% negative percentage agreement (NPA) and 100% positive percentage agreement (PPA) with sequencing results. For all 16 KPC-2 variants, GeneXpert Carba-R showed 100% NPA and 100% PPA, and the three colloidal gold immunoassays showed 100% NPA, while the PPAs of the Gold Mountainriver CGI test, Dynamiker CGI test, and NG-Test CARBA5 were 87.5%, 87.5%, and 68.8%, respectively. We also found a correlation between the mutation site in the amino acid of the variants and false-negative results by colloidal gold immunoassays. In conclusion, the GeneXpert Carba-R has been proven to be a reliable method in detecting KPC-2 and its variants, and the colloidal gold immunoassay tests offer a practical and cost-effective approach for their detection. For the sample with a negative result by a colloidal gold immunoassay test but not matching the drug-resistant phenotype, it is recommended to retest using another type of kit or the GeneXpert Carba-R assay, which can significantly improve the accuracy of detection.