The Effects of Selected Brominated and Chlorinated Chemicals onPseudomonas fluorescensPlanktonic Cells and Flow-Generated Biofilms

Zwitterionic Peptides Reduce Accumulation of Marine and Freshwater Biofilm Formers

Zwitterionic peptides are facile low-fouling compounds for environmental applications as they are biocompatible and fully biodegradable as their degradation products are just amino acids. Here, a set of histidine (H) and glutamic acid (E), as well as lysine (K) and glutamic acid (E) based peptide sequences with zwitterionic properties were synthesized. Both oligopeptides (KE)₄K and (HE)₄H were synthesized in d and l configurations to test their ability to resist the nonspecific adsorption of the proteins lysozyme and fibrinogen. The coatings were additionally tested against the attachment of the marine organisms Navicula perminuta and Cobetia marina as well as the freshwater bacterium Pseudomonas fluorescens on the developed coatings. While the peptides containing lysine performed better in protein resistance assays and against freshwater bacteria, the sequences containing histidine were generally more resistant against marine organisms. The contribution of amino acid-intrinsic properties such as side chain pK_a values and hydrophobicity, as well as external parameters such as pH and salinity of fresh water and seawater on the resistance of the coatings is discussed. In this way, a detailed picture emerges as to which zwitterionic sequences show advantages in future generations of biocompatible, sustainable, and nontoxic fouling release coatings.

Response of Formed-Biofilm of Enterobacter cloacae, Klebsiella oxytoca, and Citrobacter freundii to Chlorite-Based Disinfectants

Bacterial biofilms formed on equipment surfaces are potential sources of cross-contamination and can be responsible for the spread of bacteria involved in food spoilage, such as some Enterobacteriaceae family members. In this study, the effect of chlorite-based disinfectants, including sodium hypochlorite (SH), chlorine dioxide (CD), strongly acidic electrolyzed water (StAEW), and neutral electrolyzed water (NEW), on inactivation of mono-biofilms of Enterobacter cloacae, Klebsiella oxytoca, and Citrobacter freundii was evaluated separately. All the strains were enumerated by the viable plate-count method after disinfection for 30 min. A comparison of the surviving cells after disinfection indicated that E. cloacae biofilms were more resistant to disinfectants than the biofilms of the other two strains, and treatment with all the disinfectants improved sanitizing. SH (200 mg/L) was the most effective in the reduction of cell number in the biofilms of all strains. Considering the safety of use and environmental protection, electrolyzed oxidizing water, especially StAEW, was a good suggestion for the inactivation of cells in K. oxytoca or C. freundii biofilms. These results suggest that the cells in biofilm of E. cloacae, K. oxytoca, and C. freundii were highly sensitive to chlorite-based disinfectants and provide insights into the efficacy of disinfectants in killing bacteria.

PRACTICAL APPLICATION

The Enterobacteriaceae biofilms formed on equipment surfaces, which can cause cross-contamination and food spoilage, are greatly challenging bacterial contaminants of food products. Electrolyzed oxidizing water is a novel, environmentally friendly disinfectant that can effectively treat Enterobacteriaceae biofilms. The results of this study may be used to design effective measures to disinfect biofilms on equipment contact surfaces.

Bacterial Adhesion to Ultrafiltration Membranes: Role of Hydrophilicity, Natural Organic Matter, and Cell-Surface Macromolecules

Insight into the mechanisms underlying bacterial adhesion is critical to the formulation of membrane biofouling control strategies. Using AFM-based single-cell force spectroscopy, we investigated the interaction between Pseudomonas fluorescens, a biofilm-forming bacterium, and polysulfone (PSF) ultrafiltration (UF) membranes to unravel the mechanisms underlying early stage membrane biofouling. We show that hydrophilic polydopamine (PDA) coatings decrease bacterial adhesion forces at short bacterium-membrane contact times. Further, we find that adhesion forces are weakened by the presence of natural organic matter (NOM) conditioning films, owing to the hydrophilicity of NOM. Investigation of the effect of adhesion contact time revealed that PDA coatings are less effective at preventing bioadhesion when the contact time is prolonged to 2-5 s, or when the membranes are exposed to bacterial suspensions under stirring. These results therefore challenge the notion that simple hydrophilic surface coatings are effective as a biofouling control strategy. Finally, we present evidence that adhesion to the UF membrane surface is mediated by cell-surface macromolecules (likely to be outer membrane proteins and pili) which, upon contacting the membrane, undergo surface-induced unfolding.