Probing In Vitro Interactions between Lactococcus lactis and Mucins Using AFM

This work was devoted to the first A FM investigation of the adhesion force to pig gastric mucin (PG NI) using Lactococcus Iraqis as the model for lactic acid bacteria. The PG NI coating on polystyrene was characterized using a complementary set of multiscale analytical methods, including AFM (HarmoniX mode), XPS, and the sessile drop method. The PGM layer, which was mainly composed of C-O, C-N, COOH, CONH, and sulfur-related species (protein core and oligosaccharide side chains), was quite homogeneous and hydrophilic, with an estimated thickness of 3.4 nm. L. lactis cells were immobilized on the AFM tip (lacto probe) and used as a force probe to measure the interaction forces between bacteria and PGM-coated polystyrene on the nanoscale. Alter mucin adsorption, adhesion force levels were lower because of the interplay of electrostatic, hydrophilic, and steric repulsions. For example, the adhesion forces of the facto probe to bare and PGM-coated polymer were 0.74 +/- 0.10 and 0.12 +/- 0.06 nN, respectively. The shape analysis of retraction force distance curves highlighted the contribution of both nonspecific and specific forces (ligand/receptor bonding). The lacto probe concept and the associated A FM measurements may now provide a powerful framework for understanding interaction mechanisms between mucins and lactic acid bacteria.