Predatory bacteria - that eat others of their kind - could be a new weapon in the fight against drug-resistant bacteria or 'superbugs', a new study suggests.
A naturally occurring predatory bacterium is able to work with the immune system to clear multi-drug resistant Shigella infections in zebrafish, researchers from Imperial College London and Nottingham University in the UK said.
It is the first time the predatory bacterium Bdellovibrio bacteriovorus has been successfully used as an injected anti-bacterial therapy and represents an important step in the fight against drug-resistant infections, or 'superbugs'.
Shigella infection is responsible for over 160 million illnesses and over one million deaths every year - and is a common cause of travellers' diarrhoea.
Cases of drug-resistant Shigella are also on the rise as, although the diarrhoea usually clears up without treatment, antibiotics are often used even in mild cases to stop the diarrhoea faster.
To investigate Bdellovibrio's ability to control drug resistant Gram-negative infections, researchers injected zebrafish larvae with a lethal dose of Shigella flexneri strain M90T, resistant to both streptomycin and carbenicillin antibiotics.
Bdellovibrio was injected into the larvae's infection site and a decrease in the number of Shigella was seen.
In the absence of Bdellovibrio, zebrafish were unable to control the replication of Shigella and levels of the bacteria rose.
"This study really shows what a unique and interesting bacterium Bdellovibrio is as it presents this amazing natural synergy with the immune system and persists just long enough to kill prey bacteria before being naturally cleared," said Serge Mostowy, from Imperial College London.
"It's an important milestone in research into the use of a living antibiotic that could be used in animals and humans," Mostowy said.
Bdellovibrio can invade and kill a range of Gram-negative bacteria, such as E coli and Salmonella, in the natural environment.
Previous research has shown that it can reduce pathogen numbers in the stomach of chickens when taken as an oral therapy, but there is growing need to develop therapies to target infections in wounds and organs.
Successful use of Bdellovibrio highlights its potential uses in tackling a range of drug-resistant Gram-negative bacterial infections that can develop in hospital patients.
"This has been a truly ground-breaking collaboration that shows therapeutic Bdellovibrio in action inside the translucent living zebrafish," Professor Liz Sockett, from The University of Nottingham said.
"The predatory action of the Bdellovibrio breaks the Shigella-pathogen cells and this stimulates the white blood cells; redoubling their 'efforts' against the pathogen and leading to increased survival of the zebrafish 'patients'," said Sockett.
The study was published in the journal Current Biology.