‘Bacteria making curd can kill disease-causing mosquitoes’

A bacteria that make your homemade curd, has the potential to control the population of mosquitoes that spread viruses causing vector-borne diseases such as Japanese encephalitis and West Nile fever, and elephantiasis that afflicts Indians.

A six-year-long investigation led by the University of Mumbai – Department of Atomic Energy Centre for Excellence in Basic Sciences (UM-DAE CBS), Kalina, have identified a novel strain of bacteria belonging to the family of Enterococcus – called Enterococcus durans (E.durans), also a lactic acid bacteria – that killed the larvae of the Culex quinquefasciatus.

This species of mosquito – it is distributed in temperate and tropical regions including India- is also responsible for spreading viruses which can transmit lymphatic filariasis (elephantiasis), and bacterial disease tularaemia (rabbit fever).

In India, Culex mosquito is the main vector of elephantiasis. Studies have shown that rapid urbanisation and industrialisation in the absence of adequate drainage facilities are responsible for their presence in cities across the country.

The present study findings are important because estimates show that India alone contributes to 40% of the world’s lymphatic filariasis disease burden. Gorakhpur in Uttar Pradesh is one of the endemic states.

The World Health Organisation (WHO) describes mosquitoes as “one of the deadliest animals in the world” with incidences of mosquito-borne diseases risen approximately 30-fold over the last three decades resulting in millions of deaths across the globe.

As against physical and chemical methods such as the use of bed nets or repellents to

prevent oneself from mosquito-borne or transmitted diseases, biological control involves using one living organism to kill another.

“This is a first and promising step in identifying a bacterial strain to biologically control Culex mosquitoes. However, more studies need to be conducted to check its impact on the environment and other insects or organisms that are part of the food chain to ensure there are no adverse effects,” said Dr Abhay Chowdhary, head, department of microbiology, DY Patil University, Navi Mumbai, and former head of Haffkine Institute, who was not involved in the study.

Researchers, also from Jaipur National University, said over the last 15 years, alternative biological control through

microbial larvicides like Bacillus thuringiensis var. israelensis (Bti) and Bacillus sphaericus (Bs) have been effective and used extensively against mosquitoes that are safe to non-target organisms.

However, studies now show that both these strains are at a high risk of developing resistance in the mosquito population, and therefore it’s vital to identify novel potent and environment-friendly strains to counter the mosquito menace.

“Mosquito-borne diseases can be tackled in two ways – treat the plasmodium parasite or control the population,” said Chowdhary.

“We isolated new naturally-occurring bacteria without making any genetic modifications to it, and found it more potent against the larvae compared to the reference Bti,” said Avinash Kale, first author and reader, school of chemical sciences, UM-DAE CBS.

“Similar to Bti, we believe that a protein in E.durans kills the larvae by choking its respiratory tract,” he said.

“Further studies are needed to pinpoint the particular protein that acts on the particular protein acts on the mosquito larvae killing them,” he added.

These bacteria also have an added advantage.

Members of the Enterococcus family also constitute a

part of human-associated microbiota in mouth, skin and intestine, and therefore they are not harmful to both humans and animals.

These bacteria have also been used as probiotics in the diet of humans and farm animals, in the dairy industry, and for industrial production of cheese.

“Field trials can be undertaken by the civic body based on our work. All that has to be done is to scale up bacteria cultured in the laboratory, make it into a powder which can be sprayed on designated mosquito fields that are located away from the population,” said Kale.

“To the best of our knowledge for the first time, we report the mosquito larvicidal activity of E. durans.”

The study, which used a novel combined approach of proteomics and metabolomics on the identified E. durans strains to show the potential mosquito larvicidal components, was published in Scientific Reports (Nature Research) on March 8, 2020.