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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.

Premise plumbing promotes the regrowth and survival of opportunistic pathogens, such as Legionella pneumophila (L. pneumophila), especially within biofilms. The purpose of this study was to investigate the effectiveness of chlorine disinfection against L. pneumophila serogroup 1 and serogroup 2–15 planktonic form and biofilms. Planktonic cells were able to survive during the study period in the presence of chlorine at recommended free chlorine levels (0.2–0.5 mg/L). Biofilms were developed on galvanized steel and polyvinyl chloride (PVC) for 18 and 30 days and exposed to 50, 100, 150, and 200 mg/L for 2 hours. No colony appeared immediately after chlorination; however, persistent cells were able to tolerate treatment and continue to grow on subsequent days. The biofilm formation was evaluated by atomic force microscopy. This study demonstrates that the biofilm formed on the surfaces of plumbing materials increases bacterial resistance against high levels of chlorination. A new approach towards monitoring and eradicating L. pneumophila from water systems is required.

Background and Objectives: Legionnaires’ disease continues to be a public health concern. Colonized water distribution systems are often implicated in Legionella transmission, despite the use of various disinfection strategies, the bacterium is capable to persist and survive in water systems. The aim of this study was to investigate the persistence of Legionella pneumophila to sodium chloride over time at different temperatures and analysing the role of biofilms in the survival of this bacteria. Materials and Methods: L. pneumophila serogroup 1 and L. pneumophila serogroup 2-15 were used to study the effect of sodium chloride on planktonic and sessile cells. The tested concentrations were: 0.5%, 1%, 2%, 3%, 4%, 6% and 8% (W/V) NaCl. Biofilms were grown on 24-well microplates. Results: At 20°C, L. pneumophila planktonic cells were able to survive in sodium chloride concentrations up to 2%. How- ever, at 37°C, a sodium chloride concentration over 1.5%, reduced systematically the numbers of bacterial cells. Biofilms were grown for 20 days in the absence and presence of sodium chloride. The results show that bacterial strains were able to survive and regrow after the sodium chloride shock (2-3%). Moreover, it seems that this effect is less expressed with the age of the biofilm; old biofilms were more persistent than the young ones. Conclusion: Results from this study demonstrate that the sodium chloride disinfection strategy was effective on Legionella pneumophila planktonic cells but not on biofilms, which demonstrate the role of biofilms in the persistence and recoloniza- tion of L. pneumophila in water distribution systems.

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.

This study aims to understand the relationship between capabilities of Escherichia coli strains to form biofilm and serotype groups expressed on cell surface. Sixteen strains of E. coli were originally isolated from different food processing lines in different Moroccan cities. Strains serotyped based on their O (somatic), H (flagellar), and K (capsular) surface antigen profiles using different antiserums. Biofilm assays carried out in 96-well microtiter dishes using the method of O’Toole et al. Our results show that no clear relation observed between origin and serotype groups. In the other hand, we observed that not all studied strains were able to form biofilm. Furthermore, combination of antigens H40 and K11 appears to be involved in biofilm formation. In fact, the H antigen seems to be implicated in the placement of the bacterial cells near the surface and the K antigen may play a role in physicochemical interactions between bacteria and inert surface.

Escherichia coli surface characteristics including hydrophobicity, electrophoretic mobility and surface functional groups' composition were investigated. These characteristics were determined respectively by water contact angle measurements, microelectrophoresis and x-ray photoelectron spectroscopy (XPS). The relation between the physicochemical properties and functional groups' composition was also examined. The electrophoretic mobility at pH 7 appeared to be governed on the cell surface by the (O=C) functional groups. The cell surface's hydrophilicity was associated with high levels of (C-(O.N)) and (OH-(C-O-C)) functional groups, whereas the cell surface's hydrophobicity was associated with (C-(C,H)) functional groups. Características de superfície de Escherichia coli, tais como hidrofobicidade, mobilidade eletroforética e composição dos grupos funcionais de superfície, foram estudadas. Essas características foram determinadas por medidas de angulo de contato com água, microeletroforese e espectroscopia fotoeletrônica de raio-X (XPS), respectivamente. A relação entre as propriedades fisicoquímicas e a composição dos grupos funcionais foi também examinada. Aparentemente, a mobilidade eletroforética em pH 7 é controlada na superfície celular pelos grupos funcionais (O=C). A hidrofilicidade da superfície celular estava associada com altos níveis dos grupos funcionais [C-(O.N)] e [OH-(C-O-C)], enquanto a hidrofobicidade estava associada com os grupos funcionais [C-(C,H)].