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The choice of effective biocides used for routine hospital practice should consider the role of disinfectants in the maintenance and development of local resistome and how they might affect antibiotic resistance gene transfer within the hospital microbial population. Currently, there is little understanding of how different biocides contribute to eDNA release that may contribute to gene transfer and subsequent environmental retention. Here we investigated how different biocides affected the release of eDNA from mature biofilms of two opportunistic model strains Pseudomonas aeruginosa ATCC 27853 (PA) and Staphylococcus aureus ATCC 25923 (SA) and contribute to the hospital resistome in the form of surface and water contaminants and dust particles. The effect of four groups of biocides including alcohols, hydrogen peroxide, quaternary ammonium compounds, and polymeric guanidines were evaluated using PA and SA biofilms. Most biocides, except for PHMG-Cl and 70% ethanol, caused substantial eDNA release and PHMG-Cl was found to block biofilm development when used at concentrations of 0.5% and 0.1%. This might be associated with the formation of DNA-PHMG-Cl complexes as PHMG-Cl is predicted to bind to AT base pairs by molecular docking assays. PHMG-Cl was found to bind high molecular DNA and plasmid DNA and continued to inactivate DNA on surfaces even after four weeks. PHMG-Cl also effectively inactivated biofilm-associated antibiotic resistance gene eDNA released by a pan-drug-resistant Klebsiella strain which demonstrates the potential of PHMG-Cl as a new surface-active agent to combat the spread of antibiotic resistance in hospital settings.

Pseudomonas fluorescens SBW25 is a model soil- and plant-associated bacterium capable of forming a variety of air–liquid interface biofilms in experimental microcosms and on plant surfaces. Previous investigations have shown that cellulose is the primary structural matrix component in the robust and well-attached Wrinkly Spreader biofilm, as well as in the fragile Viscous Mass biofilm. Here, we demonstrate that both biofilms include extracellular DNA (eDNA) which can be visualized using confocal laser scanning microscopy (CLSM), quantified by absorbance measurements, and degraded by DNase I treatment. This eDNA plays an important role in cell attachment and biofilm development. However, exogenous high-molecular-weight DNA appears to decrease the strength and attachment levels of mature Wrinkly Spreader biofilms, whereas low-molecular-weight DNA appears to have little effect. Further investigation with CLSM using an amyloid-specific fluorophore suggests that the Wrinkly Spreader biofilm might also include Fap fibers, which might be involved in attachment and contribute to biofilm strength. The robust nature of the Wrinkly Spreader biofilm also allowed us, using MALDI-TOF mass spectrometry, to identify matrix-associated proteins unable to diffuse out of the structure, as well as membrane vesicles which had a different protein profile compared to the matrix-associated proteins. CLSM and DNase I treatment suggest that some vesicles were also associated with eDNA. These findings add to our understanding of the matrix components in this model pseudomonad, and, as found in other biofilms, biofilm-specific products and material from lysed cells contribute to these structures through a range of complex interactions.

The process of microbially influenced corrosion (MIC) of metallic underground constructions is often related with biofilm formation and metabolic activity of sulfur cycle bacteria. The extracellular polymeric substances (EPS) produced by these bacteria in biofilms on metallic surfaces establish the interfacial reaction space in which relevant corrosion processes occur. The EPS composition of the sulfur oxidizing bacterium Thiobacillus thioparus DSM 505 varies according to growth conditions. Presence of elemental sulfur and mild steel are demonstrated here as stimulants for variation of the EPS composition. The distribution of sugar moieties in the EPS of planktonic and biofilm grown cells of Thiobacillus thioparus DSM 505 was observed by fluorescently labeled lectin binding assays. The strongest signal was found with the PWM lectin (Pokeweed, Phytolacca americana) specific for Poly- N-Acetylglucosamine (PNAG). Cell associated proteins, visualized by Thiazine Red staining, were observed in the planktonic growth mode. Low amounts of EPS proteins from planktonic were detected. The observed influence of elemental sulfur and mild steel on the EPS composition in biofilm forming cells can be suggested to have a pivotal role in interfacial processes such as (bio) corrosion. Understanding factors that mediate changes in the composition and surface associated structural features of EPS as a consequence of working materials may help to develop a new strategy for biocorrosion prevention.