Investigations on the prevalence of colistin-resistance and their genetic determinants and localisations

Project

Project code: BfR-BIOS-08-1322-648
Contract period: 01.01.2016 - 01.12.2017
Purpose of research: Experimental development

In a recent publication Liu et al. (2015) reported for the first time on a plasmid based and transferable gene conferring resistance to colistin that was detected in enterobacteria in China. The plasmid could be transferred to other Enterobacteriaceae and Pseudomonas aeruginosa and was stable in the recipients even without further selective pressure. So far, resistance to colistin was reported to be non-transferable as genes were localized in the bacterial chromosome and could not be mobilized. The spread of bacteria carrying the plasmid and the resistance gene needs to be evaluated. Introduction into the German food animal population may lead to rapid spread as colistin is used extensively in animal production in Germany. As a prerequisite to assessing the risk for consumers more detailed knowledge on the prevalence and the characteristics of the gene and the related plasmid in different bacterial and animal species is required. Any bacteria occurring along the food animal population may be transmitted via the food chain to consumers. Exposure of consumers is related to the prevalence of the gene in animals at slaughter and the transmission of bacteria from the animals to the carcass during slaughter. So far it is not known, if bacteria harbouring this gene can colonize humans, however, the Chinese report suggests this is possible. The assessment of the relevance of this transferable resistance gene requires extensive investigations. The national resistance monitoring in zoonotic pathogens and commensals in the food chain provides a good starting point for these investigations regarding E. coli and Salmonella spp. from various food chains. Recently, a new publication describes a novel colistin resistance gene variant (mcr-2) that is also attributed to an extrachromosomal element. The respective plasmid is self-transmissible and thus of great concern for the spread of colistin resistant bacteria. Investigations will be based on PCR screening of all colistin resistant isolates for the mcr-2 gene. Positive isolates will be subjected to further analyses using whole genome sequencing for more detailed insight into the nature of this gene. Additionally, bioinformatic analysis on PacBio Genome sequences of mcr-1 encoding E. coli will be performed to generate genemaps and to submit final plasmid annotation to sequence databases like EMBL or ENA. Further microbiological analyses shall be performed to characterise the transferability and stability of mcr-2 resistance plasmids.

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