The response of a bacterial biofilm community in a simulated industrial cooling water system to treatment with an anionic dispersant

Mixed species biofilms act as planktonic cell factories despite isothiazolinone exposure under continuous-flow conditions

The primary approach to managing biofouling in industrial water systems involves the large-scale use of biocides. It is well-established that biofilms are 'cell factories' that release planktonic cells even when challenged with antimicrobials. The effect of isothiazolinone on the metabolic activity and biomass of mixed Pseudomonas biofilms was monitored in real-time using the CEMS-BioSpec system. The exposure of biofilms to the minimum inhibitory concentration (1.25 mg L-1) of biocide did not impact planktonic cell production (log 7.5 CFU mL-1), while whole-biofilm metabolic activity and biomass accumulation increased. Only the maximum biocide concentration (80 mg L-1) resulted in a change in planktonic cell yields and temporal inhibition of biofilm activity and biomass, a factor that needs due consideration in view of dilution in industrial settings. Interfacing the real-time measurement of metabolic activity and biomass with dosing systems is especially relevant to optimizing the use of biocides in industrial water systems.

Synergistic and antibiofilm activity of DNase I and glucose oxidase loaded chitosan nanoparticles against dual-species biofilms of Listeria monocytogenes and Salmonella

Salmonella and Listeria monocytogenes are two of the most common foodborne pathogens in the food industry. They form dual-species biofilms, which have a higher sensitivity to antimicrobial treatment and a greater microbial adhesion. In this experiment, we loaded DNase I and glucose oxidase (GOX) on chitosan nanoparticles (CSNPs) to explore their inhibitory effects on and disruption of dual-species biofilms of Salmonella enterica and L. monocytogenes. Transmission electron microscopy (TEM) showed that CSNP-DNase-GOX and CSNPs were spherical in shape. CSNP-DNase-GOX was shifted and altered compared to the infrared peaks of CSNPs. CSNPs loaded with DNase I and GOX showed an increase in the particle size and an alteration in the polydispersity index (PDI) and the zeta potential. Compared to free DNase I or GOX, DNase I and GOX loaded on CSNPs had higher stability at different temperatures. CSNP-DNase-GOX was more effective in inhibiting dual-species biofilms than CSNP-GOX. Scanning electron microscopy (SEM) and fluorescence microscopy were used to observe the structure of the biofilm, which further illustrated that CSNP-DNase-GOX disrupted the dual-species biofilms of S. enterica and L. monocytogenes.

Highlighting the limitations of static microplate biofilm assays for industrial biocide effectiveness compared to dynamic flow conditions

The minimal inhibitory concentration of an antimicrobial required to inhibit the growth of planktonic populations (minimum inhibitory concentration [MIC]) remains the 'gold standard' even though biofilms are acknowledged to be recalcitrant to concentrations that greatly exceed the MIC. As a result, most studies focus on biofilm tolerance to high antimicrobial concentrations, whereas the effect of environmentally relevant sub-MIC on biofilms is neglected. The effect of the MIC and sub-MIC of an isothiazolinone biocide on a microbial community isolated from an industrial cooling system was assessed under static and flow conditions. The differential response of planktonic and sessile populations to these biocide concentrations was discerned by modifying the broth microdilution assay. However, the end-point analysis of biofilms cultivated in static microplates obscured the effect of sub-MIC and MIC on biofilms. A transition from batch to the continuous flow system revealed a more nuanced response of biofilms to these biocide concentrations, where biofilm-derived planktonic cell production was maintained despite an increase in the frequency and extent of biofilm sloughing. A holistic, 'best of both worlds' approach that combines the use of static and continuous flow systems is useful to investigate the potential for the development of persistent biofilms under conditions where exposure to sub-MIC and MIC may occur.

Enhancing the Antibiofilm Activity of β-1,3-Glucanase-Functionalized Nanoparticles Loaded With Amphotericin B Against Candida albicans Biofilm

Candida biofilm-related infections cause increased morbidity and mortality in patients with a reduced immune response. Traditional antifungal therapies have proven to be insufficient as the biofilm matrix acts as a perfusion barrier. Thus, novel methods are required to improve drug delivery and kill Candida within the biofilm. In this study, chitosan nanoparticles (CSNPs) loaded with Amphotericin B (AMB), which were functionalized with β-1,3-glucanase (Gls), were fabricated (CSNPs-AMB-Gls), and their antibiofilm activity against Candida albicans biofilm was evaluated in vitro. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were employed to examine biofilm architecture and cell viability. CSNPs-AMB-Gls inhibited planktonic cell growth and biofilm formation effectively and exhibited the highest efficacy on the removal of a mature biofilm than free AMB or CSNPs-AMB. The created nanoparticles (NPs) were found to penetrate the biofilm so as to directly interfere with the cells inside and disassemble the biofilm matrix. CSNPs-AMB-Gls could also eradicate biofilms from clinical isolates. These results suggest the potential applicability of CSNPs-AMB-Gls for the treatment of Candida biofilm-related infections.

Visualizing, quantifying, and controlling local hydrodynamic effects on biofilm accumulation in complex flow paths

Complex flow paths (CFPs) are commonly applied in precision equipment to accurately supply controllable fluids with designed structures. However, the presence of biofilms in CFPs causes quite a few unwanted issues, such as bio-erosion, clogging, or even health risks. To date, visualizing and quantifying the interaction between biofilm distribution and local hydrodynamics remains difficult, and the mechanism during the process is unclear. In this paper, the remodeling simulation method (3D industrial computed tomography scanning-inverse modeling-numerical simulation) and 16S rRNA high-throughput sequencing were integrated. The results indicated that local hydrodynamic characteristics significantly affected biofilm thicknesses on CFP surfaces (relative differences of 41.3-71.2%), which inversely influenced the local turbulence intensity. The average biofilm thicknesses exhibited a significant quadratic correlation with the near-wall hydraulic shear forces (r > 0.72, p < 0.05), and the biofilm reached a maximum thickness at 0.36-0.45 Pa. On the other hand, the near-wall hydraulic shear forces not only affected microbial community characteristics of biofilms, but they also influenced the number of microorganisms involved, which determined the biofilm accumulation thereafter. The PHYLUM Firmicutes and Proteobacteria were the dominant bacteria during the process. The results obtained in this paper could provide practical conceptions for the targeted control of biofilms and put forward more efficient controlling methods in commonly applied CFP systems.

The influence of chlorination timing and concentration on microbial communities in labyrinth channels: implications for biofilm removal

Chlorination is an effective method to control biofilm formation in enclosed pipelines. To date, very little is known about how to control biofilms at the mesoscale in complex pipelines through chlorination. In this study, the dynamic of microbial communities was examined under different residual chlorine concentrations on the biofilms attached to labyrinth channels for drip irrigation using reclaimed water. The results indicated that the microbial phospholipid fatty acids, extracellular polymeric substances, microbial dynamics, and the ace and Shannon microbial diversity indices showed a gradual decrease after chlorination. However, chlorination increased microbial activity by 0.5-19.2%. The increase in the relative abundances of chloride-resistant bacteria (Acinetobacter and Thermomonas) could lead to a potential risk of chlorine resistance. Thus, keeping a low chlorine concentration (0.83 mg l^-1 for 3 h) is effective for controlling biofilm formation in the labyrinth channels.

β-1,3-glucanase disrupts biofilm formation and increases antifungal susceptibility of Candida albicans DAY185

β-1,3-glucan plays a role in Candida biofilm formation and survival of biofilm-forming Candida to stresses. In this study, we evaluated the antibiofilm activity of β-1,3-glucanase, which can degrade poly-β(1→3)-glucose of Candida albicans biofilms. Biofilm was dispersed by 55.96%. β-1,3-glucanase had no effect on Candida planktonic growth as well as adhesion. β-1,3-glucanase markedly enhanced the antifungal susceptibility of fluconazole and amphotericin B. The examination using confocal laser scanning microscopy and scanning electron microscope confirmed the antibiofilm activity of β-1,3-glucanase. Our findings demonstrate that β-1,3-glucanase may be useful as an antibiofilm agent.

Dispersal of single and mixed non-albicans Candida species biofilms by β-1,3-glucanase in vitro

β-1,3-glucan plays a role in non-albicans Candida species biofilm formation and survival of biofilm Candida to stresses. In this study, we evaluated the antibiofilm activity of β-1,3-glucanase, which can degrade poly-β(1 → 3)-glucose of non-albicans Candida species biofilms, on single and mixed species biofilm of non-albicans Candida species, including Candida tropicalis, Candida parapsilosis and Candida krusei. Biofilm by all tested species in microplate were dispersed more than 60%. β-1,3-glucanase also detached mixed species biofilm in microplate and on medical material surface. β-1,3-glucanase had no effect on Candida planktonic growth as well as adhesion. However, further biofilm formation was inhibited with β-1,3-glucanase added at 24 h after biofilm initiation. β-1,3-glucanase markedly enhanced the antifungal susceptibility of amphotericin B. The examination using confocal laser scanning microscopy and scanning electron microscope confirmed the antibiofilm activity of β-1,3-glucanase. Our findings demonstrate that β-1,3-glucanase may be useful as an antibiofilm agent.

Development and Control of Bacterial Biofilms on Dairy Processing Membranes

Membrane fouling is a major operational problem that leads to reduced membrane performance and premature replacement of membranes. Bacterial biofilms developed on reverse osmosis membranes can cause severe flux declines during whey processing. Various types of biological, physical, and chemical factors regulate the formation of biofilms. Extracellular polymeric substances produced by constitutive microflora provide an effective barrier for the embedded cells. Cultural and microscopic techniques also revealed the presence of biofilms with attached bacterial cells on membrane surfaces. Presence of biofilms, despite regular cleaning processes, reflects ineffectiveness of cleaning agents. Cleaning efficiency depends upon factors such as pH of the cleaning agent, temperature, pressure, cleaning agent dose, optimum cleaning time, and cross-flow velocity during cleaning. Among different cleaning agents, surfactants help to prevent bacterial attachment to surfaces by reducing the surface tension of water and interfacial tension between the layers. Enzymes mixed with surfactants and chelating agents can be used to penetrate the biofilm matrix formed by microbes. Recent studies have shown the role of quorum-sensing-based cell-to-cell signaling, which provides communication within bacterial cells to form a mature biofilm, and also the role of applying quorum inhibitors to prevent biofilm formation. Major cleaning applications are also summarized in Table .

Extracellular polysaccharides produced by cooling water tower biofilm bacteria and their possible degradation

The extracellular polymers (EPS) of biofilm bacteria that can cause heat and mass transfer problems in cooling water towers in the petrochemical industry were investigated. In addition, these microorganisms were screened for their ability to grow and degrade their own EPS and the EPS of other species. Twelve bacteria producing the most EPS were isolated from cooling water towers and characterized biochemically by classic and commercial systems. These were species of Pseudomonas, Burkholderia, Aeromonas, Pasteurella, Pantoea, Alcaligenes and Sphingomonas. EPS of these species were obtained by propan-2-ol precipitation and centrifugation from bacterial cultures in media enriched with glucose, sucrose or galactose. EPS yields were of 1.68-4.95 g l(-1). These EPS materials were characterized for total sugar and protein contents. Their total sugar content ranged from 24 to 56% (g sugar g(-1) EPS), and their total protein content ranged from 10 to 28% (g protein g(-1) EPS). The monosaccharide compositions of EPS were determined by HPLC. Generally, these compositions were enriched in galactose and glucose, with lesser amounts of mannose, rhamnose, fructose and arabinose. All bacteria were investigated in terms of EPS degradation. Eight of the bacteria were able to utilize EPS from Burkholderia cepacia, seven of the bacteria were able to utilize EPS from Pseudomonas sp. and Sphingomonas paucimobilis. The greatest viscosity reduction of B. cepacia was obtained with Pseudomonas sp. The results show that the bacteria in this study are able to degrade EPS from biofilms in cooling towers.

Sodium dodecyl sulfate allows the persistence and recovery of biofilms of Pseudomonas fluorescens formed under different hydrodynamic conditions

The effect of the anionic surfactant sodium dodecyl sulfate (SDS) on Pseudomonas fluorescens biofilms was investigated using flow cell reactors with stainless steel substrata, under turbulent (Re = 5200) and laminar (Re = 2000) flow. Steady-state biofilms were exposed to SDS in single doses (0.5, 1, 3 and 7 mM) and biofilm respiratory activity and mass measured at 0, 3, 7 and 12 h after the SDS application. The effect of SDS on biofilm mechanical stability was assessed using a rotating bioreactor. Whilst high concentrations (7 mM) of SDS promoted significant biofilm inactivation, it did not significantly reduce biofouling. Turbulent and laminar flow-generated biofilms had comparable susceptibility to SDS application. Following SDS exposure, biofilms rapidly recovered over the following 12 h, achieving higher respiratory activity values than before treatment. This phenomenon of post-treatment recovery was more pronounced for turbulent flow-generated biofilms, with an increase in SDS concentration. The mechanical stability of the biofilms increased with surfactant application, except for SDS concentrations near the critical micellar concentration, as measured by biofilm removal due to an increase in external shear stress forces. The data suggest that although SDS exerts antimicrobial action against P. fluorescens biofilms, even if only partial and reversible, it had only limited antifouling efficacy, increasing biofilm mechanical stability at low concentrations and allowing significant and rapid recovery of turbulent flow-generated biofilms.

Control of membrane-attached biofilms using surfactants

The effect of surfactants on membrane-attached biofilms (MABs) was studied in a lab-scale extractive membrane bioreactor (EMB). Twenty-two surfactants were screened for their potential of increasing the cell wall negative charge (i.e. the electrostatic repulsion between bacteria) of Burkholderia sp. JS150 bacterial strain. Surfactants resulting in increased bacterial negative charge were further investigated for their effects on MAB population morphology and MAB attachment behaviour. Microscopic investigation of the bacterial population in MABs showed that surfactants affect the development of flagella, suggesting changes in the attachment capability of the JS150 strain in the presence of different surfactants. Among the screened surfactants, teepol showed the best characteristics in relation to the reduction of MAB accumulation, and it was tested in an EMB system for the extraction of monochlorobenzene from a synthetic wastewater. Comparison with a control EMB, operated without surfactants under the same conditions, proved that teepol effectively reduces MAB accumulation on the membrane walls. As a result, the overall mass transfer coefficient in the presence of teepol was 53% higher than in the control EMB.

Comparison of antiadhesive and antibacterial effects of antiseptics on Streptococcus sanguinis

Three antiseptic (chlorhexidine, Olaflur, Octenisept) and one putative antiadhesive (chitosan) agent were investigated for their effect on viable planktonic and attached Streptococcus sanguinis cells. The bacterial pretreatment with each chemotherapeutic was performed in two steps: (i) After the exposure of planktonic streptococci to the antiseptics, the cells were suspended in human sterile saliva and allowed to attach to human enamel for 60 min; (ii) After 60 min in the flow chamber system, initially attached streptococci were treated with these agents. The microbial viability was monitored by the percentage of vital streptococci determined by fluorescence microscopy and cell reproduction. In comparison with the negative control NaCl, the non-bactericidal chitosan derivative showed distinctive antiadhesive properties. For both treatment procedures, the efficacy of the antiseptics in reducing the viability of planktonic and attached streptococci was Octenisept > Olaflur > chlorhexidine > saline > chitosan. Further studies appear warranted to develop new antiplaque/antibiofilm strategies involving highly efficient bactericidals with antiadhesive formulations.