How good gut bacteria wrest control from bad

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A scanning electron microscope image of Salmonella enterica bacteria. In the gut, these can cause diarrhoea, but a new study shows they’re overpowered in the presence of beneficial, microcin-secreting bacteria.
Credit: JUERGEN BERGER / Getty Images

For patients with inflammatory bowel disease (IBD), the associated pain and nausea can be a massive burden – but a helping hand may one day be in the form of tiny molecules pumped out by bacteria.

Martina Sassone-Corsi and colleagues from the University of California Irvine, US, found beneficial probiotic bacteria secrete small proteins called microcins which give them a leg-up over harmful bacteria in the gut.

The work, published in Nature, could be used to treat patients with IBD, for whom treatment options are currently both limited and non-specific.

IBD, which affects millions of people worldwide, covers a range of diseases, such as Crohn’s disease and ulcerative colitis, with symptoms including diarrhoea, vomiting, fatigue, weight loss and cramping.

These symptoms are caused by inflammation in the inner lining of the gut or within the gut wall itself.

And although the exact cause remains unknown – probably a combination of genetic, dietary and environmental factors – the bugs that colonise your gut (part of your microbiota) and the molecules they secrete, such as microcins, seem to play a leading role.

Sassone-Corsi and her crew wanted to know whether microcins could control bacterial populations in the gut – especially as good versus bad species of gut bacteria become unbalanced in IBD.

Harmful gut bacteria, such as some strains of Escherichia coli and Salmonella species, spread rapidly and overpower beneficial bacteria.

Overpopulation of a particular strain of E. coli, for instance, is linked to Crohn’s disease.

And while microcins have been shown previously to have potent antibacterial properties in the lab, their role in the body – and more specifically in the gut – remained unknown. 

So Sassone-Corsi induced bowel inflammation in mice, then inoculated them with the microcin-producing probiotic E. coli alongside an equal amount of a harmless strain of E. coli normally present in the gut, diarrhoea-inducing Salmonella enterica or a pathogenic strain of E. coli commonly found in patients with Crohn’s disease.

Probiotic E. coli colonised the inflamed gut, pushing out the disease-causing bacteria and calming inflammation. It even reduced inflammation and bacterial numbers in mice with an established Salmonella infection.

The researchers write their work may well lead to new treatments that act in the inflamed gut in IBD, displacing pathogenic bacteria from their niche and restore balance to microbial populations.

With the ever-increasing threat of antibiotic resistance, using bacteria to fight bacteria may just be the way forward.

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