Amoebae living in a creek in Mumbai are acting as a ‘Trojan horse’ harbouring and protecting multidrug resistant bacteria, according to new research.   

The study, led at the University of Strathclyde, discovered that free-living amoebae in Vashi Creek, a tidal estuary, were harbouring bacteria which had far higher levels of antimicrobial resistance (AMR) than those found in the creek’s surrounding sediment.

Nearly half of the bacteria in the amoebae were resistant to four or more antibiotics, rising to six or more in 22% of the samples. In marked contrast, the same level of resistance was found in only 0.6% of samples derived from the sediment.

Earlier detection

These findings indicate that, while they are normally predators of bacteria, amoebae could serve as “sentinel indicators” of AMR, offering the potential for earlier detection of emerging resistance threats in the environment. The researchers believe this approach aligns with the World Health Organization’s One Health strategy, which seeks a sustainable balance between the health of people, animals and ecosystems.

The work comes against the backdrop of a major global health challenge, with bacterial AMR directly responsible for an estimated 1.27 million deaths in 2019 and contributing to nearly five million deaths overall.

The research has been published in the journal Environmental Microbiology. 

Dr Ronnie Mooney, of Strathclyde’s Department of Civil and Environmental Engineering, the lead author of the paper, said: “Environmental reservoirs are increasingly recognised as key contributors to the persistence and spread of AMR, particularly in polluted systems. What we’re seeing is that these environments don’t just contain resistant bacteria; they actively shape and select them.

Protective space

“Amoebae are abundant in every environment and can act as vectors, transporting clinically relevant bacteria from the environment into high-risk areas such as hospitals or water treatment facilities without being detected. They essentially operate as a microbial Trojan Horse, giving bacteria a protective space in which to survive, adapt and strengthen their resistance.

Our research raises important questions about how these hidden reservoirs are being overlooked by current surveillance systems. If amoebae are harbouring highly resistant bacteria, then conventional monitoring approaches may not be capturing the true scale or distribution of antimicrobial resistance in the environment.

Professor Fiona Henriquez-Mui, project lead and Head of the Department of Civil and Environmental Engineering, said: “We know that antimicrobial resistance can develop and spread in the environment, and that interactions between microbes play a major role in this process. Until now, however, these interactions had not been directly linked to the relationship between amoebae and the bacteria they harbour.

“Because many clinically important bacteria are already known to survive digestion by these amoebae, we were particularly concerned that this interaction could drive the development or amplification of antimicrobial resistance in species that already pose risks to human and animal health.

Our findings suggest that these concealed reservoirs may accelerate the spread of antimicrobial resistance in precisely those bacteria we can least afford to overlook, and in ways current monitoring systems are not equipped to capture.

“We hope this research will help environmental agencies, industry and government bodies improve how they monitor antimicrobial resistance in natural and built environments.”

The study also involved partners with the University of the West of Scotland, Glasgow Caledonian University, and the Indian Institute of Technology, Bombay. It was funded by the Natural Environment Research Council, part of UK Research and Innovation, and the Department of Biotechnology Government of India.