Retention of a model pathogen in a porous media biofilm

Impacts of antibiotics on biofilm bacterial community and disinfection performance on simulated drinking water supply pipe wall

Overuse of antibiotics is accelerating the spread of resistance risk in the environment. In drinking water supply systems, the effect of antibiotics on the resistance of biofilm is unclear, and there have been few studies in disinfectant-containing systems. Here, we designed a series of drinking water supply reactors to investigate the effects of antibiotics on biofilm and bacteria in the water. At low concentrations, antibiotics could promote the growth of bacteria in biofilm; among the tested antibiotics (tetracycline, sulfadiazine and chloramphenicol), tetracycline had the strongest ability to promote this. And the antibiotic resistant bacteria (ARB) could inhibit the growth of bacteria in drinking water. Results have shown that antibiotics enhanced the bacterial chlorine resistance in the effluent, but reduced that in the biofilm. Furthermore, metagenomic analysis showed that antibiotics reduced the richness of biofilm communities. The dominant phyla in the biofilm were Proteobacteria, Planctomycetes, and Firmicutes. In tetracycline-treated biofilm, the dominant phylum was Planctomycetes. In sulfadiazine- and chloramphenicol-treated groups, bacteria with complex cell structures preferentially accumulated. The dominant class in biofilm in the ARB-added group was Gammaproteobacteria. The abundance of antibiotic resistant genes (ARGs) was correlated with biofilm community structure. This study shows that antibiotics make the biofilm community structure of drinking water more resistant to chlorine. ARGs may be selective for certain bacteria in the process, and there may ultimately be enhanced chlorine and antibiotic resistance of effluent bacteria in drinking water.

Effect of Strain-Specific Biofilm Properties on the Retention of Colloids in Saturated Porous Media under Conditions of Stormwater Biofiltration

Filter performance can be affected by bacterial colonization of the filtration media, yet little is known about how naturally occurring bacteria modify the surface properties of filtration media to affect colloidal removal. We used sand columns and simulated stormwater conditions to study the retention of model colloidal particles, carboxyl-modified-latex (CML) beads, in porous media colonized by naturally occurring bacterial strains. Colloid retention varied substantially across identical columns colonized by different, in some cases closely related, bacterial strains in a cell density independent manner. Atomic force microscopy was applied to quantify the interaction energy between CML beads and each bacterial strain's biofilm surface. We found interaction energy between CML and each strain was significantly different, with adhesive energies between the biofilm and CML, presumed to be associated with polymer-surface bonding, a better predictor of CML retention than other strain characteristics. Overall, the findings suggest that interactions with biopolymers in naturally occurring bacterial biofilms strongly influence colloid retention in porous media. This work highlights the need for more investigation into the role of biofilm microbial community composition on colloid removal in porous media to improve biofilter design and operation.

Biochar filters as an on-farm treatment to reduce pathogens when irrigating with wastewater-polluted sources

Microbial contamination of vegetables due to irrigation with wastewater-polluted streams is a common problem around most cities in developing countries because wastewater is an available source of water and nutrients but wastewater treatment is often inadequate. On-farm treatment of polluted water is a feasible option to manage microbial risks in a multi-barrier approach. Current evidence indicates good suitability of biochar filters for microbe removal from wastewater using the hydraulic loading rate (HLR) designed for sand filters, but their suitability has not been tested under on-farm conditions. This study evaluated the combined effect of several variables on removal of microbial indicators from diluted wastewater by biochar filtration on-farm and the correlations between removal efficiency and HLR. Columns of biochar with three different effective particle diameters (d₁₀) were fed with diluted wastewater at 1x, 6x, and 12x the design HLR and two levels of water salinity (electrical conductivity, EC). Influent and effluent samples were collected from the columns and analyzed for bacteriophages (ɸX174 and MS2), Escherichia coli, Enterococcus spp., and Saccharomyces cerevisiae. Microbe removal decreased with increasing HLR, from 2 to 4 to 1 log₁₀ for bacteria and from 2 to 0.8 log₁₀ for viruses, while S. cerevisiae removal was unaffected. Effective particle diameter (d₁₀) was the main variable explaining microbe removal at 6x and 12x, while EC had no effect. Correlation analysis showed removal of 2 log₁₀ bacteria and 1 log₁₀ virus at 3x HLR. Thus biochar filters on-farm would not remove significant amounts of bacteria and viruses. However, the design HLR was found to be conservative. These results, and some technical and management considerations identified, can assist in the development of a scientific method for designing biochar filters for on-farm and conventional wastewater treatment.

Efficacy of Flushing and Chlorination in Removing Microorganisms from a Pilot Drinking Water Distribution System

To ensure delivery of microbiologically safe drinking water, the physical integrity of the distribution system is an important control measure. During repair works or an incident the drinking water pipe is open and microbiologically contaminated water or soil may enter. Before taking the pipe back into service it must be cleaned. The efficacy of flushing and shock chlorination was tested using a model pipe-loop system with a natural or cultured biofilm to which a microbial contamination (Escherichia coli, Clostridium perfringens spores and phiX174) was added. On average, flushing removed 1.5–2.7 log microorganisms from the water, but not the biofilm. In addition, sand added to the system was not completely removed. Flushing velocity (0.3 or 1.5 m/s) did not affect the efficacy. Shock chlorination (10 mg/L, 1–24 h) was very effective against E. coli and phiX174, but C. perfringens spores were partly resistant. Chlorination was slightly more effective in pipes with a natural compared to a cultured biofilm. Flushing alone is thus not sufficient after high risk repair works or incidents, and shock chlorination should be considered to remove microorganisms to ensure microbiologically safe drinking water. Prevention via hygienic working procedures, localizing and isolating the contamination source and issuing boil water advisories remain important, especially during confirmed contamination events.

Escherichia coli Removal in Biochar-Modified Biofilters: Effects of Biofilm

The presence of microbial contaminants in urban stormwater is a significant concern for public health; however, their removal by traditional stormwater biofilters has been reported as inconsistent and inadequate. Recent work has explored the use of biochar to improve performance of stormwater biofilters under simplified conditions that do not consider potential effects of biofilm development on filter media. The present study investigates the role of biofilm on microbial contaminant removal performance of stormwater biofilters. Pseudomonas aeruginosa biofilms were formed in laboratory-scale sand and biochar-modified sand packed columns, which were then challenged with Escherichia coli laden synthetic stormwater containing natural organic matter. Results suggests that the presence of biofilm influences the removal of E. coli. However, the nature of the influence depends on the specific surface area and the relative hydrophobicity of filter media. The distribution of attached bacteria within the columns indicates that removal by filter media varies along the length of the column: the inlet was the primary removal zone regardless of experimental conditions. Findings from this research inform the design of field-scale biofilters for better and consistent performance in removing microbial contaminants from urban stormwater.

Abundance and Distribution of Enteric Bacteria and Viruses in Coastal and Estuarine Sediments-a Review

The long term survival of fecal indicator organisms (FIOs) and human pathogenic microorganisms in sediments is important from a water quality, human health and ecological perspective. Typically, both bacteria and viruses strongly associate with particulate matter present in freshwater, estuarine and marine environments. This association tends to be stronger in finer textured sediments and is strongly influenced by the type and quantity of clay minerals and organic matter present. Binding to particle surfaces promotes the persistence of bacteria in the environment by offering physical and chemical protection from biotic and abiotic stresses. How bacterial and viral viability and pathogenicity is influenced by surface attachment requires further study. Typically, long-term association with surfaces including sediments induces bacteria to enter a viable-but-non-culturable (VBNC) state. Inherent methodological challenges of quantifying VBNC bacteria may lead to the frequent under-reporting of their abundance in sediments. The implications of this in a quantitative risk assessment context remain unclear. Similarly, sediments can harbor significant amounts of enteric viruses, however, the factors regulating their persistence remains poorly understood. Quantification of viruses in sediment remains problematic due to our poor ability to recover intact viral particles from sediment surfaces (typically <10%), our inability to distinguish between infective and damaged (non-infective) viral particles, aggregation of viral particles, and inhibition during qPCR. This suggests that the true viral titre in sediments may be being vastly underestimated. In turn, this is limiting our ability to understand the fate and transport of viruses in sediments. Model systems (e.g., human cell culture) are also lacking for some key viruses, preventing our ability to evaluate the infectivity of viruses recovered from sediments (e.g., norovirus). The release of particle-bound bacteria and viruses into the water column during sediment resuspension also represents a risk to water quality. In conclusion, our poor process level understanding of viral/bacterial-sediment interactions combined with methodological challenges is limiting the accurate source apportionment and quantitative microbial risk assessment for pathogenic organisms associated with sediments in aquatic environments.

Decontamination of biological agents from drinking water infrastructure: a literature review and summary

This report summarizes the current state of knowledge on the persistence of biological agents on drinking water infrastructure (such as pipes) along with information on decontamination should persistence occur. Decontamination options for drinking water infrastructure have been explored for some biological agents, but data gaps remain. Data on bacterial spore persistence on common water infrastructure materials such as iron and cement-mortar lined iron show that spores can be persistent for weeks after contamination. Decontamination data show that common disinfectants such as free chlorine have limited effectiveness. Decontamination results with germinant and alternate disinfectants such as chlorine dioxide are more promising. Persistence and decontamination data were collected on vegetative bacteria, such as coliforms, Legionella and Salmonella. Vegetative bacteria are less persistent than spores and more susceptible to disinfection, but the surfaces and water quality conditions in many studies were only marginally related to drinking water systems. However, results of real-world case studies on accidental contamination of water systems with E. coli and Salmonella contamination show that flushing and chlorination can help return a water system to service. Some viral persistence data were found, but decontamination data were lacking. Future research suggestions focus on expanding the available biological persistence data to other common infrastructure materials. Further exploration of non-traditional drinking water disinfectants is recommended for future studies.

An overview on the reactors to study drinking water biofilms

The development of biofilms in drinking water distribution systems (DWDS) can cause pipe degradation, changes in the water organoleptic properties but the main problem is related to the public health. Biofilms are the main responsible for the microbial presence in drinking water (DW) and can be reservoirs for pathogens. Therefore, the understanding of the mechanisms underlying biofilm formation and behavior is of utmost importance in order to create effective control strategies. As the study of biofilms in real DWDS is difficult, several devices have been developed. These devices allow biofilm formation under controlled conditions of physical (flow velocity, shear stress, temperature, type of pipe material, etc), chemical (type and amount of nutrients, type of disinfectant and residuals, organic and inorganic particles, ions, etc) and biological (composition of microbial community - type of microorganism and characteristics) parameters, ensuring that the operational conditions are similar as possible to the DWDS conditions in order to achieve results that can be applied to the real scenarios. The devices used in DW biofilm studies can be divided essentially in two groups, those usually applied in situ and the bench top laboratorial reactors. The selection of a device should be obviously in accordance with the aim of the study and its advantages and limitations should be evaluated to obtain reproducible results that can be transposed into the reality of the DWDS. The aim of this review is to provide an overview on the main reactors used in DW biofilm studies, describing their characteristics and applications, taking into account their main advantages and limitations.

Effect of biofilm in irrigation pipes on microbial quality of irrigation water

AIMS

The focus of this work was to investigate the contribution of native Escherichia coli to the microbial quality of irrigation water and to determine the potential for contamination by E. coli associated with heterotrophic biofilms in pipe-based irrigation water delivery systems.

METHODS AND RESULTS

The aluminium pipes in the sprinkler irrigation system were outfitted with coupons that were extracted before each of the 2-h long irrigations carried out with weekly intervals. Water from the creek water and sprinklers, residual water from the previous irrigation and biofilms on the coupons were analysed for E. coli. High E. coli concentrations in water remaining in irrigation pipes between irrigation events were indicative of E. coli growth. In two of the four irrigations, the probability of the sample source, (creek vs sprinkler), being a noninfluential factor, was only 0.14, that is, source was an important factor. The population of bacteria associated with the biofilm on pipe walls was estimated to be larger than that in water in pipes in the first three irrigation events and comparable to one in the fourth event.

CONCLUSION

Biofilm-associated E. coli can affect microbial quality of irrigation water and, therefore, should not be neglected when estimating bacterial mass balances for irrigation systems.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work is the first peer-reviewed report on the impact of biofilms on microbial quality of irrigation waters. Flushing of the irrigation system may be a useful management practice to decrease the risk of microbial contamination of produce. Because microbial water quality can be substantially modified while water is transported in an irrigation system, it becomes imperative to monitor water quality at fields, rather than just at the intake.

Adhesion and biofilm formation on polystyrene by drinking water-isolated bacteria

This study was performed in order to characterize the relationship between adhesion and biofilm formation abilities of drinking water-isolated bacteria (Acinetobacter calcoaceticus, Burkholderia cepacia, Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata and Staphylococcus sp.). Adhesion was assessed by two distinct methods: thermodynamic prediction of adhesion potential by quantifying hydrophobicity and the free energy of adhesion; and by microtiter plate assays. Biofilms were developed in microtiter plates for 24, 48 and 72 h. Polystyrene (PS) was used as adhesion substratum. The tested bacteria had negative surface charge and were hydrophilic. PS had negative surface charge and was hydrophobic. The free energy of adhesion between the bacteria and PS was > 0 mJ/m(2) (thermodynamic unfavorable adhesion). The thermodynamic approach was inappropriate for modelling adhesion of the tested drinking water bacteria, underestimating adhesion to PS. Only three (B. cepacia, Sph. capsulata and Staphylococcus sp.) of the six bacteria were non-adherent to PS. A. calcoaceticus, Methylobacterium sp. and M. mucogenicum were weakly adherent. This adhesion ability was correlated with the biofilm formation ability when comparing with the results of 24 h aged biofilms. Methylobacterium sp. and M. mucogenicum formed large biofilm amounts, regardless the biofilm age. Given time, all the bacteria formed biofilms; even those non-adherents produced large amounts of matured (72 h aged) biofilms. The overall results indicate that initial adhesion did not predict the ability of the tested drinking water-isolated bacteria to form a mature biofilm, suggesting that other events such as phenotypic and genetic switching during biofilm development and the production of extracellular polymeric substances (EPS), may play a significant role on biofilm formation and differentiation. This understanding of the relationship between adhesion and biofilm formation is important for the development of control strategies efficient in the early stages of biofilm development.