Predictive role of culture-based MIC testing vs. genotyping for carbapenem-resistant Enterobacterales in a non-universal screening, highly resourced setting

Abstract

A lack of evidence of accuracy for various testing modalities for carbapenem-resistant Enterobacterales (CRE) reduces the efficiency of screening and delays the isolation of carriers. This study examined the performance of phenotypic detection of CRE in comparison to molecular testing. A cross-sectional study was conducted in an academic medical institution in Saudi Arabia on CRE-screened patients during a 36-month period (April 1, 2019, through March 31, 2022). Cases were followed up for their susceptibility status by the phenotypic gradient method and genotypes. Of 3,116 samples tested, 359 carbapenemase genes were detected in 297 strains (9.5%) belonging to 292 patients. Oxacilliniase-48 (OXA-48) was the most frequently detected genotype (n=190, 64%), followed by a combined New Delhi metallo-B-lactamase (NDM)/OXA-48 genotype (n=77, 25.9%). Variable missed isolation days were encountered for various genotypes (0-18.5 days), with an excellent clinical utility index obtained for screening the OXA-48 genotype phenotypically. The data provided some insights into the predictive role and shortcomings of the e-test alone in CRE screening. While it provided a reasonable approach in a CRE population dominated by OXA-48 genotypes, it was more likely to miss the NDM-incurred carbapenemase. Thus, local epidemiology in an institution must be considered when designing a local screening protocol in addition to consideration of cost and turnaround time.