Our gut is home to a diverse bacterial community, including Klebsiella oxytoca, which we see here on an electron micrograph. These members of the much larger Klebsiella family produce tilimycin and tilivalline, two enterotoxins that cause damage to the small intestine. At the same time however, K. oxytoca plays a positive role in colonisation resistance; the ability of the gut microbiome to inhibit the growth of harmful bacteria. In the case of K. oxytoca, these strains were already known to protect against Salmonella infections. 

A team from the German Helmholtz Institute for Infection Research, together with colleagues from other German and Austrian institutes, has elucidated how to explain these contradictory effects - damage and protection - of K. oxytoca. In Nature Microbiology, they describe two underlying mechanisms. Firstly, it all comes down to a food fight: K. oxytoca and Salmonella prey on the same nutrients and as research leader Lisa Osbelt-Block puts it, K. oxytoca is the more assertive party in that fight, causing Salmonella to simply starve. 

But that’s not the whole story. The toxins secreted by K. oxytoca also have an inhibitory effect on Salmonella. This sheds a whole new light on the role of these toxins, which until now have given K. oxytoca a bad reputation. And it offers new leads to combat Salmonella infections. The conventional way is to administer antibiotics, but these are known to also affect beneficial bacteria. Perhaps dietary modifications could also be a therapeutic option, as this would promote the growth of protective strains such as K. oxytoca. ‘Targeted reinforment of the microbiome’, as the researchers call their approach.   

Lisa Osbelt, et al., Klebsiella oxytoca inhibits Salmonella infection through multiple microbiota-context-dependent mechanisms, Nature Microbiology (2024)