The global escalation of severe infections due to carbapenemase-producing Enterobacterales (CPE) isolates has prompted increased usage of parenteral colistin. Considering the reported difficulties in assessing their susceptibility to colistin, the purpose of the study was to perform a comparative evaluation of six phenotypic assays—the colistin broth disc elution (CBDE), Vitek 2 Compact (bioMérieux SA, Marcy l’Etoile, France), the Micronaut MIC-Strip Colistin (Merlin Diagnostika GMBH, Bornheim-Hensel, Germany), the gradient diffusion strip Etest (bioMérieux SA, Marcy l’Etoile, France), ChromID Colistin R Agar (COLR) (bioMérieux SA, Marcy l’Etoile, France), and the Rapid Polymyxin NP Test (ELITechGroup, Signes, France)—versus the reference method of broth microdilution (BMD). All false resistance results were further assessed using population analysis profiling (PAP). Ninety-two nonrepetitive clinical CPE strains collected from two hospitals were evaluated. The BMD confirmed 36 (39.13%) isolates susceptible to colistin. According to the BMD, the Micronaut MIC-Strip Colistin, the CBDE, and the COLR medium exhibited category agreement (CA) of 100%. In comparison with the BMD, the highest very major discrepancy (VMD) was noted for Etest (n = 15), and the only false resistance results were recorded for the Rapid Polymyxin NP Test (n = 3). Only the PAP method and the Rapid Polymyxin NP Test were able to detect heteroresistant isolates (n = 2). Thus, there is an urgent need to further optimize the diagnosis strategies for colistin resistance.
Introduction: Infections due to carbapenemase-producing carbapenem-resistant Enterobacteriaceae (CPCRE) are an emerging global public health threat. The purpose of this study was to investigate phenotypic and genotypic features of CP-CRE strains isolated from hospitalized patients. Material and methods: Between 1st of January - 1st of July 2017, in the Department of Microbiology, “Dr. Constantin Opriş” County Emergency Hospital Baia Mare, Romania, 1110 strains of Enterobacteriaceae were isolated from bronchial secretions, urine, wounds and blood cultures. Bacterial identification and antimicrobial susceptibility tests were performed by conventional methods, Vitek 2 Compact and M.I.C.E. strips. We analysed all Enterobacteriaceae strains non-susceptible to carbapenems according to CLSI 2017 criteria. The modified Hodge test (MHT), the modified carbapenem inactivation method (mCIM) and the combination disks test (KPC, MBL, OXA-48 Confirm kit, Rosco Diagnostica) were used for phenotypic confirmation, whereas a multiplex PCR assay for genes blaKPC, blaNDM and blaOXA-48 was used for genetic confirmation. Results: 19 non-duplicate strains isolated from 16 patients were phenotypically identified as CP-CRE: Klebsiella pneumoniae (n=14), Escherichia coli (n=2), Providencia stuartii (n=2) and Serratia marcescens (n=1). Most strains were isolated from bronchial secretions (n=9). The carbapenem-hydrolizing enzymes were identified by the combination disks test as: KPC (n=9), OXA-48-like (n=5) and MBL (n=5). Molecular confirmation was performed in 18 phenotypically positive isolates with 100% concordant results with mCIM and combination disks test. Discrepant results were noticed with the MHT in case of 4 NDM-producers confirmed by PCR. All CP-CRE strains were resistant to all tested cephems. Three out of 9 K. pneumoniae strains tested against colistin were found resistant. Conclusions: The most common carbapenemase detected was KPC. Therapeutic options were limited in all positive cases. Rapid and reliable detection of CP-CRE is critical for preventing the spread of these pathogens
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