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Attraction of Brachyspira pilosicoli to mucin

Murdoch University

The anaerobic intestinal spirochaete Brachyspira pilosicoli colonises the large intestine of various species, including human beings. In the colon the spirochaete can penetrate the overlying mucus layer, attach by one cell end to the underlying enterocytes, and initiate localised colitis and diarrhoea. The aim of this study was to investigate whether, as part of the colonisation process, B. pilosicoli is attracted to mucin. Fifteen B. pilosicoli strains isolated from humans, pigs, chickens and dogs, and a control strain of Brachyspira hyodysenteriae, were analysed for their ability to enter solutions of hog gastric mucin in an in vitro capillary tube assay. No attraction was detected with 1 % mucin, but some strains started to enter a 2 % solution, and attraction then increased with increasing concentrations to peak at around 6 - 8 % mucin. A similar increase was seen with B. hyodysenteriae, although this activity peaked at 6 % mucin and then declined, suggesting that the two species have different affinities for mucin. These mucin concentrations were much higher than those used in previous experimental studies with Brachyspira species. The viscosities of the 6 - 8 % mucin solutions were around 7 - 12 mPa.s, which were similar to the measured viscosities of the mucus layer overlying the epithelium in the caecum and colon of experimental pigs. The strains varied in their motility, as assessed by their ability to enter tubes containing chemotaxis buffer, but there was no significant relationship between this motility and the extent of their ability to enter the mucin solutions. Different strains also had different propensities to enter the mucin solutions, but there were no consistent differences according to the host species of origin. B. pilosicoli strain 95/1000 was attracted towards a solution of D-serine, suggesting that chemotaxis was involved in the attraction to mucin; however, 95/1000 also was attracted to viscous solutions of polyvinylpyrillodone (PVP), in a manner mirroring the response to mucin, and hence suggesting the involvement of viscotaxis in the attraction to mucin. B. hyodysenteriae B204 showed a similar viscotaxis to PVP. Further studies are required to determine whether the in vitro interactions of a given strain with mucin is a useful indicator of its in vivo colonisation ability, and hence could be used as a potential marker for virulence.

¹ E-mail: d.hampson{at}murdoch.edu.au