The study, published in Nature Microbiology​, focused on Klebsiella pneumoniae​, described by the Imperial College scientists as “the most urgent threat to human health because many strains are resistant to multiple antibiotics, are highly virulent, cause disease in both adults and infants, and readily spread between hosts”​.

The key step in K. pneumoniae​ pathogenesis is colonization during which there are no symptoms. This asymptomatic colonization can serve as the reservoir of organisms that cause acute infection in the respiratory tract, and also be the source of K. pneumoniae​ that may be transmitted to others, they explained.

However, Bacteroidetes bacteria already present in the gastrointestinal tract may suppress K. pneumoniae​.

Immune cells called macrophages may exhibited higher bactericidal activity in the presence of Bacteroidetes stimulated IL-36, noted the researchers.

“Thus, our study provides mechanistic insight into when, where and how commensal Bacteroidetes protect against ​K. pneumoniae colonization and contagion, providing insight into how these protective microorganisms could be harnessed to confer population-level protection against ​K. pneumoniae infection,” ​they wrote.

“How the microbiota can or cannot exert colonization resistance by modulating the immune system”​

Commenting on the paper, the scientific committee of the International Probiotics Association noted that the work concerns the endogenous microbiota and it’s health effect.

“This is very nice research shedding light on how the microbiota can or cannot exert colonization resistance by modulating the immune system,” ​stated the IPA’s scientific committee. “But, this is all based on animal studies. The proof is in the pudding. Can we connect these observations to the human situation? Is prior carriage of high levels of fecal Bacteroidetes associated with a reduced K. pneumoniae carriage risk? Can we reduce encapsulation of K. pneumoniae in the respiratory tract and allow the immune system to do its work?​

“Also, anyone reading this study may make a strong distinction between commensal populations which is the subject of this study, and probiotic administration. In some future looking position can this gap be bridged? It’s a very interesting direction and begs the question or should we say further research; Can probiotic administration establish or enhance the functionality observed in certain commensal populations?”​

Intestine vs airways​

The study also looked at what happens in the upper airways and note that Proteobacteria enhanced the clearance of K. pneumoniae​ by macrophages through the IL-17A. However, K. pneumoniae​ outsmarts these defenses by forming a capsule, and thereby effectively colonizes this site.

“We reveal that microbiota development drives separate host defence programmes in the adult intestine and upper airways to inhibit colonization by the ​K. pneumoniae,” ​wrote the researchers. “This major antibiotic-resistant pathogen can overcome these defences in the upper airways but cannot compete with the microbiota in the intestine.​

“As a result of this, microbiota dysbiosis within an individual might not only promote ​K. pneumoniae colonization in that host but also promote its spread to others. Thus, the defined consortium of Bacteroidetes we identify here could provide population level protection against ​K. pneumoniae by preventing its transmission between hosts – the ultimate means of infectious disease control.”​

IPAWC + Probiota Americas 2020 The IPA World Congress + Probiota Americas will feature a range of in-depth presentations on a range of topics, including postbiotics, microbes and the mitochondria, the application of probiotics in a clinical healthcare setting, fermented foods, probiotics in sport, and much more. The IPA World Congress + Probiota Americas​​, the leading annual event for the prebiotic​, probiotic ​and the microbiota​-focused food and pharma industries in the Americas, will take place May 27-29, 2020 at the Crystal Gateway Marriott Hotel, Washington DC.

Source: Nature Microbiology​

Volume 5, Pages 304–313, doi: 10.1038/s41564-019-0640-1​

“Commensal Bacteroidetes protect against ​Klebsiella pneumoniae colonization and transmission through IL-36 signalling”​

Authors: R.P. Sequeira, et al.