Elucidating bacterial adhesion to mucosal surface by an original AFM approach

Abstract

Background Fish skin represents an ancient vertebrate mucosal surface, sharing characteristics with other mucosal surfaces including those of the intestine. The skin mucosa is continuously exposed to microbes in the surrounding water and is therefore important in the first line defense against environmental pathogens by preventing bacteria from accessing the underlying surfaces. Understanding the microbe-host interactions at the fish skin mucosa is highly relevant in order to understand and control infection, commensalism, colonization, persistence, infection, and disease. Here we investigate the interactions between the pathogenic bacteria Aeromonas salmonicida (A. salmonicida) and Yersinia ruckeri (Y. ruckeri), respectively, and the skin mucosal surface of Atlantic salmon fry using AFM force spectroscopy. Results The results obtained revealed that when retracting probes functionalized with bacteria from surfaces coated with immobilized mucins, isolated from salmon mucosal surfaces, rupture events reflecting the disruption of adhesive interactions were observed, with rupture strengths centered around 200 pN. However, when retracting probes functionalized with bacteria from the intact mucosal surface of salmon fish fry no adhesive interactions could be detected. Furthermore, rheological measurements revealed a near fluid-like behavior for the fish fry skin mucus. Taken together, the experimental data indicate that the adhesion between the mucin molecules within the mucous layer may be significantly weaker than the interaction between the bacteria and the mucin molecules. The bacteria, immobilized on the AFM probe, do bind to individual mucins in the mucosal layer, but are released from the near fluid mucus with little resistance upon retraction of the AFM probe, to which they are immobilized. Conclusion The data provided in the current paper reveal that A. salmonicida and Y. ruckeri do bind to the immobilized mucins. However, when retracting the bacteria from intact mucosal surfaces, no adhesive interactions are detected. These observations suggest a mechanism underlying the protective function of the mucosal surface based on the clearing of potential threats by adhering them to loosely attached mucus that is subsequently released from the fish skin.

Probing the expression and adhesion of glycans involved in Helicobacter pylori infection

“…Another study by Herman-Bausier et al examined the adhesion of Staphylococcus aureus collagen binding protein Cna which demonstrated binding forces of ~ 1.2 nN to collagen, which was disrupted by multiple mAbs, including 9G7, C2 and 11H11 41 . Some studies have explored using AFM to measure bacterial glycan interactions with mAbs, lectins 42 – 44 , and, with regard to H. pylori , Parreira et al demonstrated the mechanistic binding method between H. pylori blood-group binding adhesin (BabA) and Lewis B 29 . Parreira et al also highlighted the potential for AFM in the development of new targeted therapies against bacteria 28 .…”

The enhanced expression of genes encoding diguanylate cyclases under cold stress contributes to the adhesion and biofilm formation of Shewanella putrefaciens WS13

“…The adhesive force of S. putrefaciens WS13 was measured by AFM (Bioscope resolve, Bruker, Germany) as described ( 29 ).…”