Evaluation of Two Methods for the Detection of Third Generation Cephalosporins Resistant Enterobacterales Directly From Positive Blood Cultures

Abstract

Due to the importance of a rapid determination of patients infected by multidrug resistant bacteria, we evaluated two rapid diagnostic tests for the detection of third-generation cephalosporins (3GC)-resistant Enterobacterales directly from positive blood cultures within 1 h: BL-RED TM (electrochemical method) and β-LACTA TM test (chromogenic method). A panel of 150 clinical strains characterized for their resistance profiles (e.g., penicillinases, extended-spectrum beta-lactamases (ESBLs), overproduction of cephalosporinase, carbapenemases, impermeability) was tested. Approximately 100 CFU of each isolate was spiked into sterile blood culture bottles and incubated in a BD BACTEC TM FX automated system (Becton Dickinson, USA). Positive blood cultures were examined to parallel testing using the BL-RED TM and β-LACTA TM tests and conventional susceptibility method (disc diffusion following EUCAST recommendations). For all phenotypes combined, the sensitivity, specificity, positive predictive value, and negative predictive value in the detection of 3GC resistance were, respectively (i) with BL-RED TM : 45.7, 100, 100, and 54.2% and (ii) with β-LACTA TM test: 52.2, 100, 100, and 56.9%. The positivity of tests allows to adapt antibiotic treatment whereas the negative result requires other tests. Moreover, these tests detect most Ambler class A-producing Enterobacterales (KPC, ESBL, extended-spectrum OXY) with sensitivities and specificities of 87.5 and 99% for BL-RED TM , respectively and both 100% for β-LACTA TM test (47/47 isolates). These two rapid tests failed to detect AmpC overexpressed (sensitivities of 2.7% for BL-RED TM and 0% for β-LACTA TM test) and Ambler class B-producing Enterobacterales (sensitivities of 40% for both tests) notably strains without ESBLs associated (sensitivities of 0% for both tests). BL-RED TM and β-LACTA TM tests are easy-to-use and mainly attractive when a positive result is obtained notably to detect most of the Ambler class A-producing Enterobacterales in <1 h after the positivity of the blood culture, allowing a rapid adaptation of the antibiotic therapy in patients.

Antimicrobial Susceptibility of Community-Acquired Urine Bacterial Isolates in French Amazonia

“…Enterobacterales were divided into three groups according to their enzymatic resistance profile to b-lactams at the basal state (natural resistance). 12 Group I are those without enzymatic resistance at the basal state (e.g., E. coli, Proteus mirabilis), group II are those producing low-level penicillinase (e.g., K. pneumoniae, Citrobacter koseri), and group III are those producing low-level AmpC (e.g., Enterobacter spp., Serratia marcessens, Citrobacter freundii). Cross-resistance refers to resistance to several antibiotics with a similar mechanism of action.…”

Detection of Multidrug-Resistant Enterobacterales—From ESBLs to Carbapenemases

“…The successor of this principle is the commercially available BL-RED test (Coris BioConcept, Gembloux, Belgium) which is designed for the detection 3rd generation cephalosporin hydrolysis from bacterial culture or directly from positive blood cultures. Durand and colleagues challenged the test with a set of 150 Enterobacterales spiked into blood cultures and reported a good detection of 3rd generation cephalosporin resistance conferred by Ambler class A β-lactamases (sensitivity 83.3% and specificity 99.1%), but the test failed to detect 3rd generation cephalosporin resistance conferred by Ambler classes B, C and D β-lactamases [ 81 ].…”