1887

Abstract

A selective chromogenic culture medium for the laboratory isolation and differentiation of colistin resistant and spp. (CHROMagar COL- was developed, evaluated and compared to an existing selective bacterial culture medium (SuperPolymyxin).

The medium was challenged with 84 isolates, including polymyxin B (POL B)-susceptible and -resistant type strains and colistin (COL)-resistant organisms recovered from human and animal samples. Susceptibility to COL and POL B was determined by agar dilution and broth microtitre dilution. The lower limit for the detection of COL-resistant organisms was also calculated for both CHROMagar COL- and SuperPolymyxin media. The ability to isolate and correctly differentiate COL-resistant organisms within mixed cultures was also assessed and compared using both media.

Using CHROMagar COL- Gram-negative pathogens (=71) with intrinsic (=8) or acquired COL (=63) resistance were recovered with 100 % specificity down to the lower limit of detection of 10 colony-forming units (c.f.u.). The growth on SuperPolymyxin was similar, but notably weaker for COL-resistant non-fermentative bacteria ( and ). CHROMagar COL- was also more sensitive in supporting the growth of with COL resistance associated with the carriage of

CHROMagar COL- is a sensitive and specific medium for the growth of COL-resistant bacterial pathogens. Due to the low limit of detection (10 c.f.u.), it may be useful as a primary isolation medium in the surveillance and recovery of COL-resistant bacteria from complex human, veterinary and environmental samples, especially those with plasmid-mediated MCR-1 or novel mechanisms of polymyxin resistance.

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/content/journal/jmm/10.1099/jmm.0.000602
2017-11-01
2020-02-19
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