Tweet: "Colistin resistance is a global threat to bacterial infections' management. Being a last-resort antibiotic for treating of MDR Gram-negative infections, it is important to establish an efficient diagnostic method for routine use in clinical microbiology laboratories. Herein, current & emerging diagnostics for detecting colistin resistance are described to inform clinical diagnostic options." Author summary/highlights/importance  Polymyxin resistance is rapidly increasing, threatening public and veterinary healthcare.  As one of the last-line antibiotics, polymyxin must be conserved by containing the spread of polymyxin resistance.  Detecting colistin resistance relies on determining colistin MIC values by standard broth microdilution, which is labour-intensive with longer turnaround time (TAT).

Tweet: "molecular screening of patient samples collected at a national reference laboratory in Pretoria shows endemicity of carbapenemases and rarity of mcr colistin resistance genes" Impacts: Carbapenems and colistin are the last resort antibiotics available for the treatment and eradication of multidrug resistant gram-negative bacteria. Resistance in these antibiotics threaten the public health as it reduces the efficacy of these therapeutics. Klebsiella pneumoniae was identified to harbour all the identified carbapenemases. This is of concern as K. pneumoniae has a history of causing outbreaks and being endemic in healthcare facilities in South Africa. It is important to understand how common carbapenem and colistin-resistant GNB are in the healthcare facilities, as it identifies areas that require attention.

Background. The escalation of colistin resistance, due to transferable mcr-genes, threatens public and animal health as there are limited therapeutic options. Given that colistin is a last-line antibiotic, there is a need to contain the spread of its resistance to conserve its efficacy. Herein, current and emerging colistin resistance diagnostics are described to inform faster clinical diagnostic choices. Methods. A literature search in Pubmed, between 2016 and 2020, was performed. English articles evaluating colistin resistance methods/diagnostics were included. Results. Screening resulted in the inclusion of 89 journal articles. Current colistin resistance diagnostics are either phenotypic or molecular. Broth microdilution (BMD) is currently the only golden standard for determining colistin MIC values. However, other methods have been developed to overcome the challenges associated with the BMD. Phenotypic methods comprise agar-based methods i.e. ChromAgar Col-APSE, SuperPolymyxin, ChromID Colistin R etc., MIC-determiners i.e. Microscan, BD Phoenix, Sensitest colistin, Sensititre, Micronaut etc., MCR-detectors i.e. lateral flow immunoassay (LFI), chelator based assays i.e. EDTA- and DPA-based tests as well as biochemical colorimetric tests i.e. Rapid Polymyxin NP test, Rapid ResaPolymyxin NP test etc. Molecular methods only characterize mobile colistin resistance; they include PCR, LAMP, whole-genome sequencing (WGS) etc. Conclusion. Considering the efficiency (sensitivity, specificity, turnaround time) of the Rapid ResaPolymyxin NP test, it is recommended for the initial screening of colistin-resistant isolates. This can be followed by chelator-based tests or the LFI for the rapid screening of mcr-genes. However molecular assays such as LAMP, PCR may be considered for use in well-equipped clinical laboratories.