M Coppi1, A Cannatelli2, A Antonelli1, I Baccani1, V Di Pilato3, S Sennati2, T Giani2, G M Rossolini4. 1. Department of Experimental and Clinical Medicine, University of Florence, Italy. 2. Department of Medical Biotechnologies, University of Siena, Siena, Italy. 3. Department of Surgery and Translational Medicine, University of Florence, Italy. 4. Department of Experimental and Clinical Medicine, University of Florence, Italy; Clinical Microbiology and Virology Unit, Florence Careggi University Hospital, Florence, Italy. Electronic address: gianmaria.rossolini@unifi.it.
Abstract
OBJECTIVES: To evaluate a novel method, the colistin-MAC test, for phenotypic screening of acquired colistin resistance mediated by transferable mcr-1 resistance determinants, based on colistin MIC reduction in the presence of dipicolinic acid (DPA). METHODS: The colistin-MAC test consists in a broth microdilution method, in which colistin MIC is tested in the absence or presence of DPA (900 μg/mL). Overall, 74 colistin-resistant strains of Enterobacteriaceae (65 Escherichia coli and nine other species), including 61 strains carrying mcr-1-like genes and 13 strains negative for mcr genes, were evaluated with the colistin-MAC test. The presence of mcr-1-like and mcr-2-like genes was assessed by real-time PCR and end-point PCR. For 20 strains, whole-genome sequencing data were also available. RESULTS: A ≥8-fold reduction of colistin MIC in the presence of DPA was observed with 59 mcr-1-positive strains, including 53 E. coli of clinical origin, three E. coli transconjugants carrying MCR-1-encoding plasmids, one Enterobacter cloacae complex and two Citrobacter spp. Colistin MICs were unchanged, increased or at most reduced by twofold with the 13 mcr-negative colistin-resistant strains (nine E. coli and four Klebsiella pneumoniae), but also with two mcr-1-like-positive K. pneumoniae strains. CONCLUSIONS: The colistin-MAC test could be a simple phenotypic test for presumptive identification of mcr-1-positive strains among isolates of colistin-resistant E. coli, based on a ≥8-fold reduction of colistin MIC in the presence of DPA. Evaluation of the test with a larger number of strains, species and mcr-type resistance determinants would be of interest.
OBJECTIVES: To evaluate a novel method, the colistin-MAC test, for phenotypic screening of acquired colistin resistance mediated by transferable mcr-1 resistance determinants, based on colistin MIC reduction in the presence of dipicolinic acid (DPA). METHODS: The colistin-MAC test consists in a broth microdilution method, in which colistin MIC is tested in the absence or presence of DPA (900 μg/mL). Overall, 74 colistin-resistant strains of Enterobacteriaceae (65 Escherichia coli and nine other species), including 61 strains carrying mcr-1-like genes and 13 strains negative for mcr genes, were evaluated with the colistin-MAC test. The presence of mcr-1-like and mcr-2-like genes was assessed by real-time PCR and end-point PCR. For 20 strains, whole-genome sequencing data were also available. RESULTS: A ≥8-fold reduction of colistin MIC in the presence of DPA was observed with 59 mcr-1-positive strains, including 53 E. coli of clinical origin, three E. coli transconjugants carrying MCR-1-encoding plasmids, one Enterobacter cloacae complex and two Citrobacter spp. Colistin MICs were unchanged, increased or at most reduced by twofold with the 13 mcr-negative colistin-resistant strains (nine E. coli and four Klebsiella pneumoniae), but also with two mcr-1-like-positive K. pneumoniae strains. CONCLUSIONS: The colistin-MAC test could be a simple phenotypic test for presumptive identification of mcr-1-positive strains among isolates of colistin-resistant E. coli, based on a ≥8-fold reduction of colistin MIC in the presence of DPA. Evaluation of the test with a larger number of strains, species and mcr-type resistance determinants would be of interest.
Authors: Jose A Di Conza; Gabriel O Gutkind; Edgar Gonzales Escalante; Katherine Yauri Condor Journal: J Clin Microbiol Date: 2020-02-24 Impact factor: 5.948
Authors: Fernanda Esposito; Miriam R Fernandes; Ralf Lopes; Maria Muñoz; Caetano P Sabino; Marcos P Cunha; Ketrin C Silva; Rodrigo Cayô; Willames M B S Martins; Andrea M Moreno; Terezinha Knöbl; Ana C Gales; Nilton Lincopan Journal: J Clin Microbiol Date: 2017-10-04 Impact factor: 5.948
Authors: Honghui Wang; Yong Chen; Jeffrey R Strich; Steven K Drake; Jung-Ho Youn; Avi Z Rosenberg; Marjan Gucek; Patrick T McGann; Anthony F Suffredini; John P Dekker Journal: Clin Proteomics Date: 2019-02-26 Impact factor: 3.988