Evaluation of Two Tests for the Rapid Detection of CTX-M Producers Directly in Urine Samples

Abstract

Infections caused by extended-spectrum β-lactamase-producing Enterobacterales have increased rapidly and are mainly attributed to the production of CTX-M enzymes. This study evaluated the NG-Test® CTX-M MULTI lateral flow assay (CTX-M LFA) and the Rapid ESBL NP® test (ESBL NP test) for rapid detection of CTX-M-producing Enterobacterales directly in midstream urine (MSU) samples. Testing was performed on 277 clinical MSU samples in a hospital microbiology laboratory from November 2022 to January 2023; 60 of these samples (30 positive for ESBL producers and 30 positive for non-ESBL producers) were tested retrospectively after the identification and susceptibility results were obtained, and 217 samples were tested prospectively immediately after a Gram stain showing the presence of Gram-negative bacilli. The results were compared against phenotypic detection of ESBL and molecular testing as the reference methods. Overall, 67 of the 277 samples were culture-positive for ESBL-producing Enterobacterales. PCR for the blaCTX-M gene was positive for all ESBL-producing Enterobacterales isolates. All CTX-M LFA results were interpretable, while three of the ESBL NP test results were noninterpretable. The sensitivity of the CTX-M LFA (100%, 95% CI 94.6–100%) was higher than that of the ESBL NP test (86.6%, 95% CI 76.0–93.7%). Both tests had high specificities (CTX-M LFA, 99.1%, 95% CI 96.6–99.9% and ESBL NP test, 100%, 95% CI 98.2–100%). In conclusion, both the CTX-M LFA and the ESBL NP test can deliver rapid results that could improve antimicrobial stewardship for urinary tract infections.

A proof-of-principle study for the point-of-care detection of ESBL (CTX-M) by NG-Test® CTX-M MULTI lateral flow assay in urine samples using a simplified method for use in a resource-limited setting

“…This approach demonstrated a sensitivity of 100% (95% CI: 91.19%–100%) and a specificity of 95% (95% CI: 95.6%–100%) for beta-lactamase detection. 11 In our study, we observed a sensitivity of 87.5% with a specificity of 100%. A key difference in our research is that we used 1 mL of urine instead of 3 mL and included samples with a bacterial load ≥10 4 cfu/mL.…”

“…Tang et al . 11 recommend a prior enrichment step involving centrifugation of 10 mL urine at 3000 × g for 15 min, discarding the supernatant and additional incubation at 37°C for 20 min to enhance the sensitivity. However, this contradicts the POCT principle, as it requires equipment like a centrifuge and an incubator.…”

“… 10–12 However, this approach may involve enriching or pre-incubating 10 mL urine samples, demanding sophisticated instrumentation and workflow, including more hands-on time to process the samples, thus hampering the POCT approach. 11 In this study, our objective was to explore whether the procedure for detecting ESBL-E directly from urine specimens can be simplified for use in resource-limited settings. As a proof-of-principle, we conducted a head-to-head comparison of two enrichment methods, employing centrifugation and the DirecTool adapter filtration system.…”