Colistin is considered an antibiotic of last resort to treat patients with XDR GNB infections. Increasing colistin resistance is a serious challenge in clinical practice with major public health implications. Traditionally colistin resistance in K. pneumoniae was known to be chromosomally mediated involving mutations in mgrB, phoP, phoQ, pmrA, pmrB, pmrC and crrABC genes. Usage of colistin as a growth promoter in livestock farms is a well-known contributing factor to the spread of colistin resistance between animals and environment and subsequent transmission to humans. There are published reports of colistin resistance in Indian hospitals with K. pneumoniae dominating the picture and mutations in mgrB being the most common mechanism conferring colistin resistance. The authors set out to investigate the presence of colistin resistant bacteria in poultry and other raw food materials in India and to determine the possible molecular mechanisms for resistance.
Raw food samples such as poultry meat, fish, mutton meat, fruits and vegetables were collected from 22 sources-14 shops and 8 households of the Chennai metropolitan city, in the month of October and November 2017. One hundred and ten food samples (vegetables n=63, fish n=21, chicken n=19, mutton n=4, fruits n=3) were screened and 51 of these (23 vegetables, 11 fish, 12 chicken, 3 mutton, 2 fruits) were found to contain Col-R organisms. At least one sample was positive from all the 22 sources, including households that provided only vegetable samples. Of the 71 isolates screened, three E. coli (one mutton and two poultry meat samples) were found to harbour mcr-1. All the twenty-nine Col-R K. pneumoniae isolates were sequenced to determine mgrB mutations.
The authors propose that extensive usage of colistin as a growth promoter in the poultry and aquaculture and usage of poultry litter as a manure in agriculture could be the reason behind these alarming results.