A gene that confers antibiotic resistance has been found in Shigella flexneri, one of the leading causes of diarrhea. According to research published today in Applied and Environmental Microbiology, this is the first time the mrc-1 gene has been reported in Shigella flexneri.
More than 2,000 Shigella isolates were screened for the mcr-1 gene. Just one isolate tested positive. Isolation of plasmid-mediated colistin resistance in S. flexneri from animal feces on a farm suggests that it is circulating via the fecal-oral route, at least among animals on that farm, and possibly further afield via the food distribution network, according to the authors from the LIverpool School of Tropical Medicine.
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. The original host strain was also multidrug resistant, and that multidrug resistance was transferable. "This is concerning, as S. flexneri is the main cause of Shigella infections in low and middle income countries," said co-author Adam P. Roberts, senior lecturer, antimicrobial chemotherapy and resistance.
In order to try and control antimicrobial resistance, we need to understand the epidemiology of the resistance genes and how they move around," said Roberts, "This work is part of that overall effort. Now that we know mcr-1 is functional and can transfer in Shigella we can monitor this situation to see if Shigella is responsible for transfer of this gene to other species."
Citing intensive use of colistin in Chinese agriculture to boost growth of farm animals, the investigators report that the selective pressures are high enough to suggest that a large proportion of drug resistance emerged from the agriculture sector. This use has allowed for the selection, transfer, and maintenance of plasmid-mediated colistin resistance into clinical strains of E. coli, Klebsiella pneumoniae, and Salmonella spp. and rarely into other Enterobacteriaceae.
The researchers also noted that in their filter mating experiments, a host of additional mobile elements, containing multidrug resistance among much else, also transferred among microbes, suggesting that other plasmids conferring multi-drug resistance phenotypes can be acquired from the S. flexneri strain.