Mcr colistin resistance gene: a systematic review of current diagnostics and detection methods

Resistance to colistin, mediated by chromosomal mutations and more recently, by plasmid-borne mcr genes, is increasingly being reported in bacterial isolates taken from humans, animals, farms, foods, and the environment. To easily identify and contain this quickly spreading menace, efficient diagnostics that are cheaper, faster, simpler, sensitive, and specific have become indispensable and urgently necessary. A thorough and systematic review of the literature available at Pubmed, ScienceDirect and Web of Science was thus undertaken to identify articles describing novel and efficient colistin resistance- and mcr gene-detecting methods. From the final 23 studies included in this review, both phenotypic and molecular tests were found. The phenotypic tests consisted of novel culture media viz., SuperPolymyxin™, CHROMagar COL-APSE and LBJMR media, commercial automated MIC-determining instruments such as MICRONAUT-S, Vitek 2, BD Phoenix, Sensititre and MicroScan, and novel assays such as Colistin MAC test, Colispot, rapid polymxin NP test (RPNP), alteration of Zeta potential, modified RPNP test, MICRONAUT-MIC Strip, MIC Test Strip, UMIC System, and Sensitest™ Colistin. Molecular diagnostics consisted of the CT103XL microarray, eazyplex^® SuperBug kit, and Taqman^® /SYBR Green^® real-time PCR assays, with 100% sensitivity and specificity plus a shorter turnaround time (<3 hr). Based on the sensitivity, specificity, cost, required skill and turnaround time, the RPNP test and/or novel culture media is recommended for under-resourced laboratories while the Multiplex PCR or Taqman^® /SYBR Green^® real-time PCR assay alongside the RPNP or novel culture media is suggested for well-resourced ones.