Aim: To investigate the adhesion determinants of Lactobacillus plantarum Lp6, a dairy isolate.
Methods and Results: Small intestinal mucus extracted from rats was used as a substrate for adhesion. Adhesion determinants were studied by physical, chemical and enzymatic pretreatments of the bacteria, and adhesion inhibition assay. The mannose‐specific adhesins were explored by studying the effect of d‐mannose on adhesion and the yeast‐agglutinating ability of the bacteria. It was found that adhesion decreased after bacteria were treated with sodium metaperiodate, protease K, trypsin, lithium chloride and trichloroacetic acid. However, adhesion did not decrease after trypsin‐treated bacteria were incubated with cell surface protein extract. Cell surface bound exopolysaccharides were found to inhibit the adhesion. d‐mannose inhibited the adhesion in a dose‐dependent manner. The bacteria could significantly agglutinate yeast and lost this ability after protease K treatment.
Conclusions: Adhesion was mainly mediated by the mannose specific adhesins, which might be proteins that reversibly bind to the cell surface components. Cell surface‐bound exopolysaccharides were also involved in adhesion.
Significance and Impact of the Study: The mannose‐specific adhesion of Lact. plantarum Lp6 to rat mucus might be important for competing with pathogens‐binding sites in gut, which may be used to resist the colonization of the pathogens.
Summary
Lactobacillus plantarum proliferates inefficiently in milk, mainly because of its lack of cell envelope proteases and its inability to hydrolyse proteins in milk. Our previous study showed that this strain could grow well in milk with the addition of oat and malt extracts. To investigate the usage and preference for polypeptides and oligopeptides for this strain, sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), o‐phthaldialdehyde (OPA), high‐performance liquid chromatography (HPLC), plate counting and other methods were used in this study. The results showed that proteins in fermented milk cannot be absorbed and utilised by L. plantarum, whereas polypeptides and oligopeptides provide available nitrogen sources for their growth. Short‐chain peptides were more conducive to absorption and utilisation than long‐chain peptides. In particular, peptides with molecular weights in the range of 200–1400 Da in the oat extract and 100–700 Da in the malt extract were preferentially absorbed and utilised.
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