Aquaculture is popular in India. We now produce more than five million tonnes of freshwater fish. To prevent bacterial diseases in fish farms, antibiotics are used. This can lead to multidrug resistant bacteria in fish from the farms as in the case of poultry that is farmed.
To check whether this is true, Gaurav Rathore and team, National Bureau of Fish Genetic Resources, Lucknow collaborated with colleagues from the Shri Ramswaroop Memorial University, Lucknow.
They collected samples from local fish farms and retail fish markets in Lucknow. To check for bacterial contamination, they took swabs from the gills of the fishes, and inoculated bile esculin broth with bacteria extracted from the swabs. The researchers cultured the bacteria and selected cultures containing Enterococcus faecalis, a pathogenic microbe capable of developing antimicrobial resistance.
They screened the culture samples for gelatinase and biofilm production, key indicators of tissue invasion and bacterial virulence. The strains collected from the fish market formed coloured colonies in the culture media suggesting biofilm production and high virulence. To find the genes responsible for the virulence, the researchers screened the resistant phenotypes using polymerase chain reaction.
Then, they tested the susceptibility of the bacteria cultured to nine commonly used antibiotics. Bacteria from fish collected directly from farms showed no signs of multidrug resistance. But bacteria from fish markets showed high antimicrobial resistance.
The researchers tracked the supply chain from the fish farms to the market. They found that the fish were infected during transportation to the fish market.
“To prevent the spread of multidrug resistant pathogens, fish traders need to improve sanitation and implement safe handling protocols during transportation,” says Arti Dwivedi, ICAR-National Bureau of Fish Genetic Resources, Lucknow.
“The findings highlight the potential for using E. faecalis as a bioindicator for monitoring and analysing fish quality,” adds Gaurav Rathore, her mentor.
Biologia, published online on 17th June 2025;
DOI: 10.1007/s11756-025-01949-w
Reported by Meera K M
Centre for Marine Living Resources and Ecology, Kochi
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