If transferred to a pathogen, these genes could spawn a new drug-resistant bacterium
Bacteria in sediments of Sunderban mangrove have genes that withstand antibiotics, a research team has discovered1. The Bose Institute team found that the continual flow of effluents and water-borne pollutants to these delta waters contributed to the development of antibiotic-resistant genes (ARGs).
The researchers correlated pollutants such as harmful heavy metals and polycyclic aromatic hydrocarbons (PAHs) with diversity of ARGs. Analysis of the pollutants showed their origins in farm run-off, industrial effluents, domestic waste and the effects of tourism. “Our understanding of the effect of pollution also involves how it affects the natural environment, far from densely populated areas,” said lead researcher, Abhrajyoti Ghosh.
Antibiotics kill pathogenic bacteria that frequently infect humans and domestic animals. Exposure to a combination of a host and antibiotics triggers mutations in bacterial genes, creating ARGs. This, however, doesn’t explain the origins of all such genes because some possibly evolve in microbes that grow in natural environments2.
This led the Kolkata team to search for ARGs in natural environments such as the Sundarban mangrove. The researchers collected sediment samples from five islands – Godkhali, Kalash, Sushnir Char, Lothian Island and Bonnie Camp.
They found that Godkhali sediments had the highest abundance of bacteria such as Rhizobium and Marinobacter that degrade PAHs. PAH-degrading bacteria such as Arthrobacter and Cycloclasticus were most abundant in Sushnir Char. They identified 42 ARGs, in various levels, in these bacteria. Of these, 17 and 25 resistance genes were enriched or depleted respectively.
Their analysis suggested that heavy metalsand PAH pollution selectively increased the abundance of the resistance genes. “Since no new antibiotics have been recently developed, pollutants seem to be major drivers that accelerate evolution of ARGs,” said Paola Grenni, microbial ecologist at the Water Research Institute of National Research Council in Rome, who is not associated with the study. “Once these resistance genes are in the environment, they spread among bacterial species between habitats and even migrate between connected aquatic ecosystems, and also spread to pathogens,” Grenni said.