Evaluation of a Lateral Flow Immunoassay for Rapid Detection of CTX-M Producers from Blood Cultures

Abstract

Bacteremia caused by extended-spectrum β-lactamases-producing Enterobacterales has increased rapidly and is mainly attributed to CTX-M enzymes. This study aimed to evaluate the NG-Test® CTX-M MULTI lateral flow assay (CTX-M LFA) for rapid detection of CTX-M producers in blood cultures (BCs) positive for Gram-negative bacilli in spiked and clinical BCs. Retrospective testing was performed on BC bottles spiked with a collection of well-characterized Enterobacterales isolates producing CTX-M (n = 15) and CTX-M-like (n = 27) β-lactamases. Prospective testing of clinical, non-duplicate BCs (n = 350) was performed in two hospital microbiology laboratories from April 2021 to March 2022 following detection of Gram-negative bacilli by microscopic examination. Results were compared against molecular testing as the reference. In the spiked BCs, the CTX-M LFA correctly detected all CTX-M producers including 5 isolates with hybrid CTX-M variants. However, false-positive results were observed for several CTX-M-like β-lactamases, including OXY-1-3, OXY-2-8, OXY-5-3, FONA-8, -9, -10, 11, 13 and SFO-1. In clinical BCs, the CTX-M LFA showed 100% (95% CI, 96.0–100%) sensitivity and 99.6% (97.9–100%) specificity. In conclusion, this study showed that rapid detection of CTX-M producers in BC broths can be reliably achieved using the CTX-M LFA, thus providing an opportunity for early optimization of antibiotics.

First report and characterization of a plasmid-encodedblaSFO-1in a multi-drug resistantAeromonas hydrophilaclinical isolate

“…We report the first clinical isolate of an Aeromonas species encoding bla SFO-1 from a multi-drug resistant strain in the USA. It is possible that the frequency of SFO in clinical isolates may be underreported due to misidentification as CTX-M in lateral flow assays [54]. Isolate MAH-4 contained numerous ESBLs both chromosomally and on a 327 kb mobilizable plasmid.…”

Genomic Investigation of Salmonella Typhi in Hong Kong Revealing the Predominance of Genotype 3.2.2 and the First Case of an Extensively Drug-Resistant H58 Genotype

“…The MIC (µg/mL) was interpreted as follows: azithromycin (sensitive ≤ 16, resistant ≥ 32) and ciprofloxacin (sensitive ≤ 0.06, intermediate 0.12–0.5, resistant ≥ 1). A double disc synergy test was used for the phenotypic detection of ESBL, in which ceftriaxone discs were placed 25 mm away from a 20/10 µg amoxicillin/clavulanate disc [ 20 ]. A clear extension of the edge of the inhibition zone towards the disc containing clavulanate was interpreted as positive for ESBL production.…”

“…With the post-pandemic travelling boom, there is a high risk of the global dissemination of drug-resistant Salmonella Typhi, which calls for an urgent need for the development of rapid diagnostics that can accurately predict the susceptibility of the infecting strain [ 19 ]. For example, a lateral flow immunoassay for the extended-spectrum β-lactamase (ESBL) CTX-M has been shown to have excellent sensitivity and specificity for the rapid detection of CTX-M-producing Enterobacterales in blood culture [ 20 ]. Until the wide availability of rapid diagnostic tests, knowledge of the local, regional, and global distribution of antimicrobial resistance in Salmonella Typhi remains crucial for guiding empirical treatment and public health interventions.…”

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

“…All the bacterial isolates from the MSU samples were identified to the species level with susceptibility testing and detection of ESBL production as described below. All the Enterobacterales and other Gram negative bacterial isolates were further tested for the bla CTX-M gene using CTX-M subgroup-specific multiplex polymerase chain reaction (PCR) assays as previously described [14,17].…”

“…The NG-Test ® CTX-M MULTI test (NG-Biotech Laboratories, Guipry, France) is a lateral flow assay (CTX-M LFA) that uses a cocktail of monoclonal antibodies to detect all five groups of CTX-M enzymes [12]. Apart from testing isolated bacterial colonies, both tests have been evaluated for direct detection of ESBLs from positive blood culture broths with good performance [13,14]. However, data on their performance in direct detection of ESBLs in urine specimens is lacking.…”