A team of investigators has found that the mcr-1 drug resistance gene, which encodes resistance to a drug that is used as a last resort, has been found for the first time in Shigella flexneri. Shigella are one of the leading causes of diarrhea worldwide. The research is published March 2nd in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.

In the study, the investigators screened more than 2,000 Shigellaisolates for the mcr-1 gene. (Isolates are bacteria from samples which in this case were taken from animal feces on a farm, from patients, and from the environment). Just one isolate tested positive.

That may sound scarce; however, ." as only a small number of strains (<10%) were isolated from farm and urban environments, we were surprised to find one with mcr-1 on a transferable plasmid, which is a relatively high frequency of detection compared to the clinical strains

Isolation of plasmid-mediated colistin resistance in S. flexnerifrom animal feces on a farm suggests that it is circulating via the fecal-oral route at least amongst animals on that farm, and possibly further afield via the food distribution network," according to the report. "In addition, it suggests that farm environments may be an unrecognized reservoir of S. flexneri.

Through a technique called "filter mating," the investigators found that the plasmid was capable of jumping from S. flexneri to a strain of Escherichia coli. (It can likely also jump to other Shigella species, and to other genera of bacteria.)

The original host strain was also multidrug resistant, and that multidrug resistance was also transferable, according to the report. "This is concerning, as S. flexneri is the main cause of Shigellainfections in low and middle income countries

Source: American Society for Microbiology.