Role of Surface Coverage of Sessile Probiotics in Their Interplay with Pathogen Bacteria Investigated by Digital Holographic Microscopy.

The adhesion of probiotics plays an important role in the gastrointestinal tract. Understanding the effect of the coverage of colonized probiotics on enteric pathogens is critical for the design of effective probiotic therapies. In the present work, we have investigated the adaptive behaviors of the intestinal pathogenic bacteria Enterobacter sakazakii (ES) near the surfaces coated with a probiotic─ Lactobacillus rhamnosus GG (LGG) as a function of surface coverage ratio ( CR LGG ) by using a home-setup digital holographic microscopy. It shows that ES cells can adaptively sense LGG within a distance of 4.2 μm, even at CR LGG values as low as 0.05%. The growth inhibition of ES cells slightly varies with CR LGG , but the near-surface acceleration and accumulation of ES cells have much dependence on CR LGG . As CR LGG increases from 0.05 to 24.6%, the percentage of actively swimming ES, the motion bias, the acceleration, and the interplay duration do not linearly vary with CR LGG . Instead, each of them shows an extreme at CR LGG of 13.4%, corresponding to the chemotaxis behaviors of ES cells induced by diffusing stimuli (organic acids, bacteriocins, etc. ) released from LGG, which showed an extreme concentration gradient at CR LGG = 13.4% by simulations. Our study clearly demonstrates that surface coverage of sessile probiotics profoundly influences their interplay with pathogen bacteria, which should be taken into account in designing probiotic therapies.