The diagnostic accuracy of the GeneXpert ESBL-ampC prototype assay for rapid PCR-based detection of extended-spectrum beta-lactamase genes directly from urine

The emerging prevalence of extended-spectrum beta-lactamase (ESBL) producing Enterobacterales has implications for the empirical treatment of common infections, such as complicated urinary tract infections. To provide adequate treatment, while avoiding empirical therapy with last resort carbapenems, rapid identification of ESBL-containing pathogens is desirable. Routine urine samples were collected between February and July 2021 in two Dutch clinical medical microbiology laboratories according to a predefined list containing certain culture characteristics. All urine samples were screened for the presence of ESBL genes (bla(CTX-M2), bla(CTX-M14), and bla(CTX-M15)) with random-access quantitative PCR (qPCR) using the Cepheid GeneXpert ESBL-ampC prototype assay. The qPCR and microbiological culture results were compared. After the calculation of the sensitivity and specificity, discrepancies were investigated by whole-genome sequencing. In total, 276 urine samples were available for ESBL analysis (94 ESBL culture positive and 182 ESBL culture negative). The sensitivity and specificity for detection of ESBL genes were 90.4% and 98.4%, respectively. In nine samples (9.6%), no ESBL genes were detected with GeneXpert, while in the microbiological culture, an ESBL-positive organism was isolated. This was mainly explained by non-GeneXpert ESBL genes: bla(SHV)-family (n = 6; 75.0%), bla(TEM)-family (n = 1; 12.5%), and bla(SRT)-family (n = 1; 12.5%). The positive and negative predictive values in a hypothetical clinical scenario with a 15% ESBL prevalence were 0.91 and 0.98, respectively. Regarding ampC, the specificity appears to be satisfactory, but the sensitivity is low. The Cepheid GeneXpert ESBL assay could be beneficial for the fast and accurate detection of ESBL genes in regions where the epidemiology of ESBL genes coincides with the targets in the panel.

Automated summary

The increasing prevalence of ESBL-producing Enterobacterales has implications for the empirical treatment of common infections. Rapid identification of ESBL-containing pathogens is desirable to provide effective treatment without resorting to last resort antibiotics.