Interfacial re-arrangement in initial microbial adhesion to surfaces

Upon initial microbial adhesion to a surface, multiple events occur that include interfacial re-arrangements in the region between an adhering organism and a surface. Application of physico-chemical mechanisms to explain microbial adhesion to surfaces requires better knowledge of the interfacial re-arrangement occurring immediately after adhesion than hitherto available.     

Antiadhesive action of a marine microbial surfactant

The antiadhesive action of a lipopeptide biosurfactant from a marine bacterium was investigated. The effect of cultivation conditions on the adhesion property of few bacterial strains was studied. It was observed that the static cultures showed greater adhesion due to scarcity of oxygen. The biosurfactant upon surface conditioning was found to be effective in removal of the microbial adhesion at a concentration as low as 0.1 g L⁻¹. The percentages of inhibition of adhesion against different test bacterial strains ranged from 15 to 89% using 0.1–10 g L⁻¹ of purified biosurfactant. These percentages of adhesion inhibition were found to be significantly higher than the previously reported values. The antiadhesive efficacy of the biosurfactant was also evident from confocal laser scanning microscopy studies.     

A critical flux to avoid biofouling of spiral wound nanofiltration and reverse osmosis membranes: Fact or fiction?

The relation between biofouling and membrane flux in spiral wound nanofiltration and reverse osmosis membranes in drinking water stations with extensive pretreatment such as ultrafiltration has been studied. The flux – water volume flowing through the membrane per unit area and time – is not influencing the development of membrane biofouling. Irrespective whether a flux was applied or not, the feed spacer channel pressure drop and biofilm concentration increased in reverse osmosis and nanofiltration membranes in a monitor, test rigs, a pilot scale and a full-scale installation. Identical behavior with respect to biofouling and feed channel pressure drop development was observed in membrane elements in the same position in a nanofiltration installation operated with and without flux. Calculation of the ratio of diffusive and convective flux showed that the diffusive flux is considerably larger than the convective flux, supporting the observations that the convective flux due to permeate production is playing an insignificant role in biofouling. Since fouling occurred irrespective of the actual flux, the critical flux concept stating that “below a critical flux no fouling occurs” is not a suitable approach to control biofouling of spiral wound reverse osmosis and nanofiltration membranes.     

抗菌生物材料的研究进展

生物材料的感染限制了生物材料的进一步应用.细菌在材料表面粘附、生长成细菌生物膜是生物材料相关感染难治的根本原因.因此,最有效的解决方法是防止细菌生物膜的形成.本文对目前抗菌生物材料的研究现状进行综述,提出目前防止细菌生物膜生成的方法主要有三种:抗细菌粘附的方法;杀菌的方法及二者相结合的方法.在设计抗粘附生物材料时,除了考虑材料表面的化学结构外,也要考虑材料的表面拓扑结构及材料的本体性能对细菌粘附的影响;在设计杀菌的生物材料时,不但要考虑杀菌性能,也要考虑杀菌剂对材料血液相容性的影响.总的来说,抗粘附的方法及杀菌相结合(多重抗菌)的方法是可望解决生物材料感染的一条新方法.     

Homogentisic acid γ-lactone suppresses the virulence factors of Pseudomonas aeruginosa by quenching its quorum sensing signal molecules

Homogentisic acid γ-lactone exhibited excellent anti-quorum sensing (QS) and anti-biofilm activities against Pseudomonas aeruginosa. Moreover, it suppressed the QS-dependent virulence factors in P. aeruginosa by quenching its QS signal molecules.     

Chemical and physical methods for characterisation of biofilms

Research on biofilms has developed into interdisciplinary work, in which scientists from different fields are involved. This review summarizes the state- of-the-art including models due to different aspects of biofilms. Techniques for characterization of surfaces and interfaces, e.g. microscopic, spectroscopic and microsensoric methods will be presented. In addition, procedures that involve sampling of biofilms and subsequent separation of the components for their analysis are a part of this article. Analytical methods are summarized for the investigation of extracellular polymeric substances (EPS), mainly polysaccharides beside proteins in the microbial host. Finally, procedures for the analysis of minerals as components of biofilms are presented.     

Study of biofilm formation by total-reflection X-ray fluorescence spectrometry

A total reflection X-ray fluorescence spectrometric method was developed for elemental analysis of natural biofilms grown on polycarbonate substrates in the Lake Velence. For the duration of 9 weeks long growing period, two substrates were removed weekly from the lake and investigated by analytical and algological methods. The total biomass production achieved its highest value after 7 weeks. Ca, Sr and Ti, as well as Fe, Mn, K and Zn showed their maximum concentrations in the biofilms after 5 and 6-7 weeks, respectively. The enrichment factors of the 6 weeks old biofilm for the detected seven elements amounted to 10³-10⁴. The recommended colonization time for biomonitoring of the Lake Velence is 6 weeks applying polycarbonate substrates.     

Preventing biofilm development on DGT devices using metals and antibiotics

The DGT technique has potential as a tool for monitoring reactive phosphorus in freshwater aquaculture effluents. Because those waters have high concentrations of suspended matter and nutrients, biofilms may form on the surface of the DGT devices. Those biofilms may hinder the movement of reactive phosphorus and hence interfere with the DGT measurements. We tested two antibiotics, glutaraldehyde and chloramphenicol, two metal-iodides, copper and silver and also two alternative filter types, nucleopore membrane and silver-based filters, to evaluate their respective potential to prevent the formation of algae. The treatment with silver iodide seems to affect the properties of the diffusive gel and changes the flux measurements of the DGT device. The DGT response observed using the copper iodide and chloramphenicol treatments was not significantly different from the control. Glutaraldehyde changed the macroproperties of the diffusive gel and interfered with the phosphorus detection using spectrophotometric determinations. The effect of the anti-biofilm treatments on the DGT measurements was independent of pH and ionic strength of the water. For the field deployment in fish farms, copper and silver were the best anti-biofilm agents. Copper prevented algal colonisation for 14-days post-deployment and the response was unaffected by the anti-biofilm agent throughout this period. Silver was even better and prevented biofilm formation up to a 21-days post-deployment. Conversely, chloramphenicol did not prevent algal colonisation for the 14- and 21-days deployments. However, for deployments longer than 14 days, it was difficult to obtain consistently good results for all of anti-biofilm agents tested, due to the high concentration of suspended matter in the freshwater effluents of the fish farms tested. This approach suggests a metal pre-treatment of the membrane filters is useful to prevent biofilm formation for DGT deployments aimed at P measurements. DGT deployments for metal measurements would likely require a different approach.     

Quantitative and morphological analysis of biofilm formation on self-assembled monolayers

In spite of intensive studies over the past two decades, the influence of surface properties on bacterial adhesion and biofilm formation remains unclear, particularly on late steps. In order to contribute to the elucidation of this point, we compared the impact of two different substrates on the formation of bacterial biofilm, by analysing bacterial amount and biofilm structure on hydrophilic and hydrophobic surfaces. The surfaces were constituted by NH₂- and CH₃-terminated self-assembled monolayers (SAMs) on silicon wafers, allowing to consider only the surface chemistry influence because wafers low roughness. A strain of Escherichia coli K12, able to produce biofilm on abiotic surfaces, was grown with culture durations varying from 4 h to 336 h on both types of substrates. The amount of adhered bacteria was determined after detachment by both photometry at 630 nm and direct counting under light microscope, while the spatial distribution of adhered bacteria was observed by fluorescence microscopy. A general view of our results suggests a little influence of the surface chemistry on adherent bacteria amount, but a clear impact on dynamics of biofilm growth as well as on biofilm structure. This work points out how surface chemistry of substrates can influence the bacterial adhesion and the biofilm formation.