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Biofilm formation and microbial adhesion are two related and complex phenomena. These phenomena are known to play an important role in microbial life and various functions with positive and negative aspects. Actinobacteria have wide distribution in aquatic and terrestrial ecosystems. This phylum is very large and diverse and contains two important genera Streptomyces and Mycobacteria. The genus Streptomyces is the most biotechnologically important, while the genus Mycobacteria contains the pathogenic species of Mycobacteriaceae. According to the literature, the majority of studies carried out on actinomycetes are focused on the detection of new molecules. Despite the well-known diversity and metabolic activities, less attention has been paid to this phylum. Research on adhesion and biofilm formation is not well developed. In the present review, an attempt has been made to review the literature available on the different aspects on biofilm formation and adhesion of Actinobacteria. We focus especially on the genus Streptomyces. Furthermore, a brief overview about the molecules and structures involved in the adhesion phenomenon in the most relevant genus is summarized. We mention the mechanisms of quorum sensing and quorum quenching because of their direct association with biofilm formation.

Microbial adhesion to surfaces is thought to involve physicochemical interactions between the substrate and microbial cells. Understanding the physicochemical aspects involved in the adhesion phenomenon, as a critical step in biofilm formation, is essential to finding ways to prevent their formation and control biocontamination risks. The aim of this study was to investigate the relation between the adhesion behavior of 12 Escherichia coli strains isolated from food and their surface hydrophobicities using qualitative ( θ w ) and quantitative (ΔGiwi) approaches. The surface physicochemical properties of both bacterial cells and glass material were estimated through contact angle measurements. The adhesive behavior of E. coli strains on a glass surface was assessed. The results showed a good logarithmic relation between the percentage of the adhered cells and their surface hydrophobicity with the quantitative approach ΔGiwi; however, qualitative hydrophobicity ( θ w ) appeared to demonstrate no effect regarding adhesion behavior. This work lays the foundation for future studies and opens an important debate on the mechanisms underlying the adhesion behavior of E. coli strains by using the thermodynamic approach (ΔGiwi) as an important model of hydrophobicity that could explain and predict better bacterial adhesion ability.