Détection rapide des β-lactamases à Spectre Elargi: Etude comparée du β-LACTA TM Test, du NG-TEST CTXM MULTI et de l’Automate ePlex® de Genmark.

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Résumé

Background: Enterobacteriaceae are the main germs responsible for bloodstreams and urinary tract infections. These bacteria became a global threat because of their multidrug resistance, essentially due to the Extended Spectrum Beta-lactamase (ESBL) acquisition. The purpose of this study is to evaluate, the diagnostic performances of three tests in the rapid detection of ESBL from urine and blood cultures samples. Methods: Over a period of five months, the ePlex® and MALDI-TOF-MS automated systems were used to identify bacteria from blood culture and urine samples positive to Gram-negative bacilli to the microscopic exam. Simultaneous detection of CTX-M resistance genes was performed on the ePlex® automated system. The detection of ESBLs was done by immunochromatographic (NG-Test-CTXM MULTI) and chromogenic (β-LACTATM Test) tests. The culture on agar media with an antibiotics susceptibility test including the search for ESBL by a synergy test was the reference technique. Results: A total of 51 urine samples and 46 blood cultures, all positive for Gram-negative bacilli on microscopic exam were included. Enterobacteriaceae accounted for 98% (50/51) and 69.5% (32/46) of isolates in UTIs and bacteremia, respectively, with E. coli leading 72.5% (37/51) and 45.6% (21/46). ESBL-producing Enterobacteriaceae accounted for 22% (11/50) of the isolates in UTIs versus 28.1% (9/32) in bacteremias. The identification concordances between ePlex® and MALDI-TOF-MS after isolation were between 92 and 98% in both types of samples. Among the 11 ESBL-producing uropathogenic strains, the β-LACTATM, the ePlex®, the NG-Test-CTXM MULTI detected 9; 9 and 10 respectively. One ESBL-producing E. coli (non-CTX-M) was not detected by ePlex®, NG-Test-CTXM MULTI and β-LACTATM. No false positives were found with these three tests. The sensitivity (Se), specificity (Sp), positive predictive value (PPV) and negative predictive value (NPV) were 82%, 100%, 100% and 95% for β-LACTATM and ePlex, respectively. The NG-Test-CTXM MULTI showed a Se, Sp, PPV and NPV of 91%, 100%, 100% and 98% respectively. Among the 9 ESBL strains from blood cultures, they were all detected by the β-LACTATM test and the NG-Test-CTXM MULTI while the ePlex® detected 8/9 of them. For the 37 non ESBL GNB in blood cultures, no false positives were recorded in these 3 tests. The performance of β-LACTATM test and NG-Test-CTXM MULTI for the detection of ESBL was similar: Se, Sp, PPV and NPV at 100% while ePlex® had Se, Sp, PPV and NPV of 89%, 100%, 100% and 97%. Conclusion: The Gram-negative panel of ePlex® is well adapted to the rapid diagnosis of Enterobacteriaceae and the identification of associated resistance genes. However, the simplicity and lower cost of the β-LACTATM tests as well as the NG-Test-CTXM MULTI make them effective alternatives in the rapid diagnosis of ESBL-producing enterobacteria.

Mots-clés

ESBL, CTXM, β-LACTA test, ePlex