Abstract:
The emergence of polymyxin resistance, due to transferable mcr genes, threatens public
and animal health as there are limited therapeutic options. As polymyxin is one of the
last-line
antibiotics, there is a need to contain the spread of its resistance to conserve its
efficacy. Herein, we describe current and emerging polymyxin resistance diagnostics to
inform faster clinical diagnostic choices. A literature search in diverse databases for studies
published between 2016 and 2020 was performed. English articles evaluating colistin
resistance methods/diagnostics were included. Screening resulted in the inclusion of 93
journal articles. Current colistin resistance diagnostics are either phenotypic or molecular.
Broth microdilution is currently the only gold standard for determining colistin MICs
(minimum inhibitory concentration). Phenotypic methods comprise of agar-based
methods
such as CHROMagar™ Col-APSE,
SuperPolymyxin, ChromID® Colistin R, LBJMR
and LB medium; manual MIC-determiners
viz., UMIC, MICRONAUT MIC-Strip
and
ComASP Colistin; automated antimicrobial susceptibility testing systems such as BD
Phoenix, MICRONAUT-S,
MicroScan, Sensititre and Vitek 2; MCR-detectors
such as
lateral flow immunoassay (LFI) and chelator-based
assays including EDTA-and
DPA-based
tests, that is, combined disk test, modified colistin broth-disk
elution (CBDE),
Colispot, and Colistin MAC test as well as biochemical colorimetric tests, that is, Rapid
Polymyxin NP test and Rapid ResaPolymyxin NP test. Molecular methods only characterize
mobile colistin resistance; they include PCR, LAMP and whole-genome
sequencing.
Due to the faster turnaround time (≤3 h), improved sensitivity (84%–100%)
and specificity (93.3%–100%)
of the Rapid ResaPolymyxin NP test and Fastinov®, we recommend
this test for initial screening of colistin-resistant
isolates. This can be followed
by CBDE with EDTA or the LFI as they both have 100% sensitivity and a specificity of
≥94.3% for the rapid screening of mcr genes. However, molecular assays such as LAMP
and PCR may be considered in well-equipped
clinical laboratories.
