Type: Research Essays
Sample donated: Pamela Dennis
Last updated: May 23, 2019
Introduction One of the mostdiverse and abundant microbial niches is found in the human body. TheGram-negative anaerobe Akkemansiamuciniphila, which belongs to the Planctomycetes-Verrucomicrobia-Chlamydiaesuperphylum, is present in the alimentary canal of more than 90% of theanalyzed cases. A. muciniphila isespecially adapted to the human gut environment and uses glycosolated proteinsof the epithelial mucus layer as its C and N source. Earlier studies indicatethat A.
muciniphila is related to guthealth; i.e. a low density of A.
muciniphila is related to diabetes type 1,Crohn’s disease (CD) and in Ulcerative colitis (UC), both during remission andin clinically active disease, than in vigorous individuals. Furthermore, A.muciniphila is related to restoration of the thickness of the mucos layer inthe intestines and reducing endotoxemia. State of the art The evidence ofthe positive effect of A.muciniphila on gut health increases but less is know about the interactionsbetween the host and the bacterium and how it copes with differentcircumstances. The interaction of the bacteria and its hosts starts with colonizing in which they can adhere by binding to the mucus layer of theintestines epithelium or via the cells underneath, the enterocytes.
To whichsurface A. muciniphila adheres hasn’tbeen studied yet even as the ability of coping with an oxygen rich environment.This study will answer which mechanisms A. muciniphila uses to adhere tothe mucus layer or the epithelium cells of the gastrointestinal tract. Recent findings Although the humancolon consists out of an anaerobic microbe community, it turned out that A.
muciniphila is capable of survivingin both oxic as well as anoxic conditions. As A. muciniphila is aerotolerant, contrasting incubation conditions were comparedin an adhesion experiment. The binding efficiency with epithelial cells HT29 and Caco-2 do not differ between aerobicand anaerobic atmosphere. Thus, A.muciniphila does not have to be treated as a true anaerobe, but is able tocope with oxygen. Also, it turnedout that the only significant binding of A.muciniphila, compared to BSA, occurred with laminin.
The bindingprocess of A. muciniphila with other extracellular matrix (ECM) proteins, was not significant. Asthe adhesion between A. muciniphila andthe intestinal mucus is less than 1%, it can be stated that there is noadhesion at all. As other bacteria, for example L. rhamnosus and B. bifidum,show strong connection to human colonic mucus, it was unexpected that A.
muciniphila did not. An explanationfor this is that these species do not utilize and degrade the mucus, like A. muciniphila does. Although theadhesion of A. muciniphila and L.
rhamnosus on colonic mucus was notcompareble, A. muciniphila adhered toboth enterocrytes equally well as L.rhamnosus. This might indicate that the enterocytes are true binding sitesfor A. muciniphila. A.
muciniphila and B. fragilis were both cocultivated for 24 hours and indicated an expansionin transepithelial electricalresistance (TER). Compared to the Caco-2 cultures, without bacteria the TER ofCaco-2 cocultures of Escherichia coli declinedsignificantly.
This shows that at this timepoint E. coli cells increased and that there is no cell suspension forthe OD600 values of A. muciniphilaand B. fragilis, which indicatesa stagnation of growth. The positive impact of cell monolayer integrity for thefirst 24 hours was the most succesfull with B.
fragilis, followed by A. muciniphila. After 48 hours the transepithelial electrical resistance of Caco-2 cocultures of A. muciniphila became equal to the coculturesof B. fragilis. During the 48 hour incubation the cell density of B.
fragilis and A. muciniphila did not diversify, neither seems thatthe bacteria are severly compromised. Under the same circumstances, E. coliaffected TER development negatively and the coculture increased during thesecond 24 hours, which will probably result in a further decline of the transepithelial electrical resistance in E.
coli cocultures. Earlier studieshave associated obesity and diabetes to decreased gut health and inflammation,which result in lipopolysaccharide (LPS) induced endotoxemia. When LPS isreleased, enterocytes start producing the chemokine interleukin-8 (IL-8) whichleads to inflammation. Needless inflammation can cause disorder in theintestinal epithelium and can disturb the homeastasis of the colonal mucus.Compared to the IL-8 production by E.coli, A. muciniphila produced less IL-8 in HT-29 cells. Thus, there willbe no strong inflammation when A.
muciniphila is present in the gastrointestinal tract. Since there almostwas no inflammatory response in the presence of A.muciniphila, it was checkedwether it does or does not produce LPS and whether it is different compared to E.coli. The results show that A.
muciniphila does produce LPS, howeverit does not activate HT-29 cells to produce a lot of interleukin-8. Therefor it islikely that the produced LPS by A. muciniphila is different compared to that of E. coli. Discussion The results ofthis study show that A. muciniphila does not bind to the intestinal mucus butprefers to bind to the epithelial cells Caco-2 and HT-29 and the ECM laminin.
It remains unknown howthis organism is able to live in this constantly changing environment andshould be studies to answere this question. A possible justification could bethat A. muciniphila releases a certainenzyme which decreases the colonic mucus, making it hard for the bacteria toeffectively bind to the mucus.
As A. muciniphila was able to bind to the extracellularmatrix laminin it might suggest that pathogens are competing with A. muciniphila for bindingsites atlocations where the epithelial cell layer of the colon is damaged. Furthermore, it is likely that A. muciniphila isable to strengthen the barier of the intestinal track. Future research couldstudy the helpful role of A.
muciniphila inconnection with its host in for example obesity and diabetes.