Multiple surface interaction mechanisms direct the anchoring, co-aggregation and formation of dual-species biofilm between and .

Introduction: Polymicrobial biofilms have a significant impact on pathogenesis of infectious microorganisms. Many human diseases are affected by colonization of multi-species communities affecting negatively the treatments and increase the risks for the health. In particular, in the epithelium of the stomach co-existence between and has been described, which has been associated to a synergistic effect on ulcer pathogenesis.

Objective: The objective of this work was to advance in the understanding of surface interaction between and for the formation of polymicrobial biofilms.

Methods: Studies of microbial surfaces both bacterium, yeast and co-cultures of them were carried out by infrared spectroscopy, deconvolution analysis, transmission and scanning electron microscopies, and optic microscopy. Additional methods were used to contrast the results as dynamic light scattering, contact angle, agarose gel electrophoresis and gene amplification.

Results: Several surface interaction mechanisms promote the anchoring of on , cell co-aggregation, and polymicrobial biofilm formation, main identified interactions were: (i) hydrophobic interactions between non-polar peptide chains and lipid structures, characterized by among 84.9 ± 1.6 (γ = 22.78 mJ/m with 95.3 of dispersive contribution) and 76.6 ± 3.8 (γ = 17.34 mJ/m, 40.2 of dispersive contribution) for and , respectively, (ii) hydrogen bonds between surface components of yeast and bacterium (e.g., -S-H⋅⋅⋅NH- or -S-H⋅⋅⋅O[bond, double bond]CO-) and (iii) thiol-mediated surface interactions identified by displacements to lower wavenumbers (Δ = 5 cm). Evidence of internalization and electrostatic interactions were not evidenced. All observations were congruent with the biofilm formation, including the identification of small-size biostructures (i.e., 122-459 nm) associated with extracellular proteins, extracellular DNA, or outer membrane vesicles were observed characteristic of biofilm formation.

Conclusion: It is concluded that biofilm is formed by co-aggregation after anchoring of on . Several surface interactions were associated with the prevalence of , the possibility to find in the stomach epithelium infected by , but also, strength interactions could be interfering in experimental observations associated with bacterial-DNA detection in culture mixtures.