Pulsed ultra-violet inactivation spectrum of Escherichia coli

Inactivation of Escherichia coli is examined using ultra-violet (UV) radiation from a pulsed xenon flashlamp. The light from the discharge has a broadband emission spectrum extending from the UV to the infrared region with a rich UV content. The flashlamp provides high-energy UV output using a small number of short-duration pulses (30 micros). The flashlamp is used with a monochromator to investigate the wavelength sensitivity of E. coli to inactivation by the pulsed UV light. Using 8 nm wide pulses of UV radiation, the most efficient inactivation is found to occur at around 270 nm and no inactivation is observed above 300 nm. A pyroelectric detector allows the energy dose to be determined at each wavelength, and a peak value for E. coli population reduction of 0.43 log per mJ/cm(2) is measured at 270 nm. The results are compared with the published data available for continuous UV light sources.     

Recovery of Escherichia coli in fresh water fish, Jenynsia multidentata and Bryconamericus iheringi

Escherichia coli concentration was determined in digestive tract and muscle of Jenynsia multidentata and Bryconamericus iheringi through bioassays. Field experiments were also conducted with J. multidentata collected in the Suquía River, Córdoba, Argentina. E. coli was quantified by the most probable number, using lauryl sulphate tryptose broth with 4-methylumbelliferyl-beta-D-glucuronide. For bioassays, E. coli concentrations 10(2), 10(3), 10(4), 10(5), 10(6)CFU/ml were introduced in aquarium water. E. coli was recovered from the digestive tracts of J. multidentata and B. iheringi in all the concentrations assayed. Bacterial critical load in water for the recovery of bacteria from muscle, was 10(3)CFU/ml for both species. The regression analysis between E. coli loads in water and those found in digestive tract and muscle showed a positive linear relationship for J. multidentata and B. iheringi. The same relation was observed between the concentration of bacteria in digestive tract and muscle in both species. In field experiments, E. coli was recovered from digestive tract and muscle of J. multidentata. The presence of E. coli in the studied fish suggests that they can carry bacteria to non-polluted waters. However, further studies are necessary to evaluate its significance for public and environmental health.     

Relative survival of Escherichia coli and Salmonella typhimurium in a tropical estuary

Microcosm studies have been carried out to find out the relative survival of Escherichia coli and Salmonella typhimurium in a tropical estuary. Survival has been assessed in relation to the important self-purifying parameters such as biotic factors contained in the estuarine water, toxicity due to the dissolved organic and antibiotic substances in the water and the sunlight. The results revealed that sunlight is the most important inactivating factor on the survival of E. coli and S. typhimurium in the estuarine water. While the biological factors contained in the estuarine water such as protozoans and bacteriophages also exerted considerable inactivation of these organisms, the composition of the water with all its dissolved organic and inorganic substances was not damaging to the test organisms. Results also indicated better survival capacity of E. coli cells under all test conditions when compared to S. typhimurium.     

Genetic diversity of Escherichia coli isolates in irrigation water and associated sediments: implications for source tracking

Identifying the sources of fecal contaminants in surface water bodies such as rivers and lakes is of significant importance for environmental quality, food safety and regulatory purposes. Current DNA library-based source tracking approaches rely on the comparison of the genetic relatedness among the fecal contaminants. The objective of this study was to determine the genetic relatedness of Escherichia coli isolated from irrigation water and associated sediments using pulse field gel electrophoresis (PFGE) and to evaluate the genetic stability of the E. coli PFGE patterns. The isolates were obtained over a 4-month period from specific locations within irrigation canals and sediments associated with the Rio Grande River along the Texas-Mexico border. Fifty E. coli isolates were genotyped using PFGE. Different E. coli genotypes were identified among samples collected in 11 different locations. Some isolates obtained over successive months showed similar genotypic patterns. In the laboratory experiment, the PFGE pattern of one E. coli strain changed during survival in irrigation water. The genetic relatedness of this strain changed from >95% to <83% over 8-week survival. These results imply that PFGE is of such extreme resolution that it may be a challenging task to rely solely on a PFGE-based source tracking DNA fingerprint library for large watersheds.     

Escherichia coli, enterococci, and Bacteroides thetaiotaomicron qPCR signals through wastewater and septage treatment

Fecal indicators such as Escherichia coli and enterococci are used as regulatory tools to monitor water with 24 h cultivation techniques for possible input of sewage or feces and presence of potential enteric pathogens yet their source (human or animal) cannot be determined with routine methods. This critical uncertainty has furthered water pollution science toward new molecular approaches. Members of Bacteroides genus, such as Bacteroides thetaiotaomicron are found to have features that allow their use as alternative fecal indicators and for Microbial Source Tracking (MST). The overall aim of this study was to evaluate the concentration and fate of B. thetaiotaomicron, throughout a wastewater treatment facility and septage treatment facility. A large number of samples were collected and tested for E. coli and enterococci by both cultivation and qPCR assays. B. thetaiotaomicron qPCR equivalent cells (mean: 1.8 × 10⁷/100 mL) were present in significantly higher concentrations than E. coli or enterococci in raw sewage and at the same levels in raw septage. The removal of B. thetaiotaomicron target qPCR signals was similar to E. coli and enterococci DNA during the treatment of these wastes and ranged from 3 to 5 log₁₀ for wastewater and was 7 log₁₀ for the septage. A significant correlation was found between B. thetaiotaomicron marker and each of the conventional indicators throughout the waste treatment process for both raw sewage and septage. A greater variability was found with enterococci when compared to E. coli, and CFU and equivalent cells could be contrasted by various treatment processes to examine removal and inactivation via septage and wastewater treatment. These results are compared and contrasted with other qPCR studies and other targets in wastewater samples providing a view of DNA targets in such environments.     

Ability of three DNA-based assays to identify presumptive Escherichia coli colonies isolated from water by the culture-based mFC agar method

We tested the ability of three PCR assays, targeting uidA and tuf genes to correctly identify Escherichia coli colonies isolated from water and we compared them to two β-glucuronidase-based culture methods (Colilert^® and Readycult^®), in terms of specificity and sensitivity. E. coli isolates recovered on mFC agar were first tested for the presence of the uidA positive colonies were presumed to be E. coli. For further characterization, uidA-negative colonies were subsequently identified using the Vitek 2 automated system. Colilert^® and Readycult^® detected 436 and 442 of 468 colonies identified as E. coli on mFC corresponding to sensitivities of 93.2 and 94.4%, respectively. None of the 59 non-E. coli isolates was detected by both methods for a specificity of 100%. Two (2) uidA and 1 tuf PCR assays were also tested. The uidA PCR assays yielded positive signals for 447 (95.5%) and 434 (92.7%) of 468 E. coli isolates tested respectively, whereas the tuf PCR assay showed a sensitivity of 100%. None of the 59 non-E. coli isolates was detected by both uidA PCR assays (100% specificity), whereas tuf PCR false-positive signals were obtained with Escherichia fergusonii and Escherichia albertii. However, since these 2 species are principally found in the feces of mammals and birds, their detection indicates a fecal contamination. Consequently, using a 1-h tuf rtPCR assay to confirm the identity of E. coli colonies on mFC agar is as specific, more sensitive, and potentially more cost-efficient than culture methods based on β-glucuronidase detection.     

Removal and recovery of uranium from aqueous solutions by Trichoderma harzianum

Removal and recovery of uranium from dilute aqueous solutions by indigenously isolated viable and non-viable fungus (Trichoderma harzianum) and algae (RD256, RD257) was studied by performing biosorption-desorption tests. Fungal strain was found comparatively better candidate for uranium biosorption than algae. The process was highly pH dependent. At optimized experimental parameters, the maximum uranium biosorption capacity of T. harzianum was 612 mg U g(-1) whereas maximum values of uranium biosorption capacity exhibited by algal strains (RD256 and RD257) were 354 and 408 mg U g(-1) and much higher in comparison with commercially available resins (Dowex-SBR-P and IRA-400). Uranium biosorption by algae followed Langmuir model while fungus exhibited a more complex multilayer phenomenon of biosorption and followed pseudo-second-order kinetics. Mass balance studies revealed that uranium recovery was 99.9%, for T. harzianum, and 97.1 and 95.3% for RD256 and RD257, respectively, by 0.1M Hydrochloric acid which regenerated the uranium-free cell biomass facilitating the sorption-desorption cycles for better economic feasibility.     

Escherichia coli virulence genes profile of surface waters as an indicator of water quality

We compared the presence of 58 known virulence genes (VGs) associated with Escherichia coli strains causing intestinal (InPEC) and extra-intestinal (ExPEC) infections in three estuarine, four brackish and 13 freshwater sites during the dry and wet seasons. The most common VGs observed in water samples during the dry season belonged to ExPEC (traT; 80% and ompA; 70%) whilst east1 (70%) gene was the most common among InPEC. More types of VGs were observed in water samples during wet season and included those found among InPEC (e.g. eaeA; 100%; fyuA, 90%; paa, 65%; cdt, 60%; and stx₂, 60%) and ExPEC (e.g. iroN_E.coli, 90%; iss, 90% and kpsMTII, 80%). Eight VGs were found exclusively in the wet season, of which four were found in all three water types indicating their association with storm-water run off. The number of VGs associated with ExPEC were significantly (P < 0.05) higher in only brackish and estuarine waters during the wet season compared to the dry season. There was no correlation between the number of E. coli and the presence of VGs in any of the water types in both seasons but we found similarities in VG profiles of sites with similar land uses.     

Optimization of DGGE community fingerprinting for characterizing Escherichia coli communities associated with fecal pollution

We evaluated the use of DGGE fingerprinting to differentiate communities of Escherichia coli from animal and geographic sources. An initial screening of 15 gene candidates revealed the ability of three target genes (mdh, phoE and uidA-4) to effectively differentiate E. coli communities originating in horses, pigs, geese and goats. Cluster and jackknife analyses performed on the communities from a more extensive number of hosts (n = 150) including humans (via raw sewage), horses, pigs, geese and cows revealed that the internal accuracy of classification of E. coli community fingerprints to their origin was similar for each of the three genes (85-86%). Each of the three genes were tested for their ability to associate E. coli source- and sink communities in two settings featuring contaminated water; (i) a stream receiving municipal wastewater effluent and (ii) a pond inhabited by geese. For each gene, DGGE fingerprints effectively matched effluent- and downstream E. coli communities (98-100% similarity) and excluded upstream communities, while communities from goose fecal material were 77-79% similar to communities in pond water, indicating fecal inputs from geese. Furthermore, each gene discriminated against E. coli communities from hosts non-indigenous to either setting. DGGE analysis of E. coli communities appears to be a promising tool to augment existing efforts aiming to address the dynamics of bacteria pollution in complex, natural environments.     

Hydroxyapatite-supported Ag-TiO2 as Escherichia coli disinfection photocatalyst

A series of hydroxyapatite (HAP), 1wt% Ag-TiO(2) (AT1), 1wt% Ag-HAP and 5wt% AT1/HAP composite catalysts were prepared by incipient wetness and mechanical mixing methods. They were characterized by X-ray diffraction (XRD), FT-IR, SEM and ESCA analyses and their photocatalytic bactericidal activities were measured in suspension using Escherichia coli (E. coli), a water pollutant indicator. The surface analysis revealed that the Ag/Ti ratio is found to be ca. 0.0273 and also it indicated that the titania is present in the form of Ti(4+) and Ag is present as metallic silver. Both the XRD and ESCA analyses confirmed the phase of metallic Ag particles, which played a significant role on the bactericidal activity of the Ag doped TiO(2) catalysts. The FT-IR analysis of HAP revealed that the peak intensity is due to the absorbance of surface PO(4)(3-) group centered at wave number 1030cm(-1) and is drastically decreased upon exposure to UV for 1h. The HAP displayed high amount of bacteria adsorption, ca. 80% during the dark experiments compared to other catalytic systems tested. The cumulative photocatalytic properties of AT1/HAP catalytic system resulted in 100% E. coli bacteria reduction within 2min.     

Influence of tetracycline resistance on the transport of manure-derived Escherichia coli in saturated porous media

In this research, tetracycline resistant (tet^R) and tetracycline susceptible (tet^S) Escherichia coli isolates were retrieved from dairy manure and the influence of tetracycline resistance on the transport of E. coli in saturated porous media was investigated through laboratory column transport experiments. Experimental results showed that tet^RE. coli strains had higher mobility than the tet^S strains in saturated porous media. Measurements of cell surface properties suggested that tet^RE. coli strains exhibited lower zeta potentials than the tet^S strains. Because the surface of clean quartz sands is negatively charged, the repulsive electrostatic double layer (EDL) interaction between the tet^R cells and the surface of sands was stronger and thus facilitated the transport of the tet^R cells. Although no difference was observed in surface acidity, cell size, lipopolysaccharides (LPS) sugar content and cell-bound protein levels between the tet^R and tet^S strains, they displayed distinct outer membrane protein (OMP) profiles. It was likely that the difference in OMPs, some potentially related to drug efflux pumps, between the tet^R and tet^S strains led to alteration in cell surface properties which in turn affected cell transport in saturated porous media. Findings from this research suggested that manure-derived tet^RE. coli could spread more widely in the groundwater system and pose serious public health risks.     

A model for predicting resuspension of Escherichia coli from streambed sediments

To improve the modeling of water quality in watersheds, a model is developed to predict resuspension of Escherichia coli from sediment beds in streams. The resuspension rate is expressed as the product of the concentration of E. coli attached to sediment particles and an erosion rate adapted from work on sediment transport. The model uses parameter values mostly taken from previous work, and it accounts for properties of the flow through the bottom shear stress and properties of the sediment through the critical shear stresses for cohesive and non-cohesive sediment. Predictions were compared to resuspension rates inferred from a steady mass balance applied to measurements at sixteen locations in a watershed. The model’s predictions matched the inferred rates well, especially when the diameter of particles to which E. coli attach was allowed to depend on the bottom shear stress. The model’s sensitivity to the parameters depends on the contributions of particle packing and binding effects of clay to the critical shear stress. For the current data set, the uncertainty in the predictions is controlled by the concentration of E. coli attached to sediment particles and the slope used to estimate the bottom shear stress.     

Detection of virulence genes in Escherichia coli of an existing metabolic fingerprint database to predict the sources of pathogenic E. coli in surface waters

A collection of 366 Escherichia coli strains from 10 host groups and surface waters were tested for the presence of 15 virulence genes associated with strains causing intestinal and extra-intestinal infections. The virulence genes included eaeA, VT1, 2 and 2e, LT1, ST1 and 2, Einv gene, EAgg gene, CNF1 and 2, papC, O111 and O157 side chain LPS. Of the 262 strains obtained from nine different hosts, 39 (15%) carried one or more of these virulence genes. These included six strains from humans, two from horses, eight from dogs, two from ducks, five from cattle, seven from chickens, four from pigs, two from sheep and three from deer. Of the remaining 104 strains obtained from water samples, 10 (10%) also carried one or more of the tested virulence genes. Of these, six had identical biochemical phenotypes (BPTs) to strains isolated from humans (two strains), dogs (two strains), chickens (one strain) and sheep (one strain) with 4 BPTs also carrying same virulence genes. Our results indicate that the sources of clinically important E. coli strains found in surface waters due to faecal contamination can be predicted by using a combination of biochemical fingerprinting method and the detection of virulence genes. From the public health point of view this information will be of great importance for evaluating the risk associated with public use of the catchment.     

DNA extraction and Escherichia coli quantification of anaerobically digested biosolids using the competitive touchdown PCR method

Accurate enumeration of indicator organisms such as Escherichia coli is important for assessing the safety of water and wastewater samples. Recent research has shown that E. coli can enter a viable but non-culturable state; therefore, traditional cultivation methods could potentially underestimate the quantities of the organisms. The goals of the research were to develop and verify a DNA extraction protocol and a quantitative polymerase chained reaction (PCR) method for E. coli enumeration in digested biosolids. A solvent-based DNA extraction protocol with extensive cell lysis recovered approximately 78-84% of spiked DNA. In comparison, a commercial kit only recovered 28-42% of DNA, likely from inefficient cell lysis. The developed competitive touchdown PCR (cPCR) method for E. coli enumeration was comparable to both real-time PCR (rt-PCR) and cultivation methods with sensitivity of approximately 50,000-500,000 E. coli per gram dry solids (DS), which is suitable for Class B biosolids monitoring in the US and "conventional" biosolids in the European Union. The cPCR protocol provides a less expensive alternative than the rt-PCR as a culturing independent method for enumerating E. coli.     

Microbial toxicity of metal oxide nanoparticles (CuO, NiO, ZnO, and Sb2O3) to Escherichia coli, Bacillus subtilis, and Streptococcus aureus

In this study, the microbial toxicities of metal oxide nanoparticles were evaluated for Escherichia coli, Bacillus subtilis, and Streptococcus aureus in laboratory experiments. The nanoparticles tested were CuO, NiO, ZnO, and Sb₂O₃. The metal oxide nanoparticles were dispersed thoroughly in a culture medium, and the microorganisms were cultivated on Luria-Bertani agar plates containing different concentrations of metal oxide nanoparticles. The bacteria were counted in terms of colony forming units (CFU). The CFU was reduced in a culture medium containing metal oxide NP, and the dose-response relationship was characterized. CuO nanoparticles were found to be the most toxic among the tested nanoparticles, followed by ZnO (except S. aureus), NiO, and Sb₂O₃ nanoparticles. We determined that the intrinsic toxic properties of heavy metals are also associated with the toxicity of metal oxide nanoparticles. Ion toxicity was also evaluated to determine the effects of metal ions dissolved from metal oxide NPs, and the toxicity induced from the dissolved ions was determined to be negligible herein. To the best of our knowledge, this is the first study of the toxicity of NiO and Sb₂O₃ NPs on microorganisms. We also discuss the implications of our findings regarding the effects of the intrinsic toxic properties of heavy metals, and concluded that the apparent toxicities of metal oxide NPs can largely be understood as a matter of particle toxicity.     

Deer diet affects ribotype diversity of Escherichia coli for bacterial source tracking

Ribotyping is one of a number of genotypic methods for bacterial source tracking. This method requires a host origin database of one bacterial species be established in order to identify environmental isolates. Researchers establishing these databases have observed considerable ribotype diversity within a specific bacterial species. One source of this diversity may be diet. We determined the effect of diet on ribotype diversity for Escherichia coli in penned and wild deer (Odocoileus virginianus) in a 13-ha forested watershed. A total of 298 E. coli isolates was obtained, 100 from penned deer, 100 from wild deer, and 98 from the stream in the watershed to which all deer had access. The wild deer had significantly more ribotypes (35) than the penned deer (11 ribotypes, p = 0.05). This result suggests that diet affected ribotype diversity, and that a host origin database for bacterial source tracking should contain bacterial isolates from wild rather than from captive animals. Also, 42 of 98 (42.9%) environmental isolates matched penned and wild deer ribotypes. If bacterial source tracking determines that fecal contamination is predominantly from wildlife, then it may be unnecessary to monitor these watersheds because control over wildlife is difficult.     

Evaluation of data from the literature on the transport and survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated conditions

Escherichia coli and thermotolerant coliforms are of major importance as indicators of fecal contamination of water. Due to its negative surface charge and relatively low die-off or inactivation rate coefficient, E. coli is able to travel long distances underground and is therefore also a useful indicator of fecal contamination of groundwater. In this review, the major processes known to determine the underground transport of E. coli (attachment, straining and inactivation) are evaluated. The single collector contact efficiency (SCCE), eta0, one of two parameters commonly used to assess the importance of attachment, can be quantified for E. coli using classical colloid filtration theory. The sticking efficiency, alpha, the second parameter frequently used in determining attachment, varies widely (from 0.003 to almost 1) and mainly depends on charge differences between the surface of the collector and E. coli. Straining can be quantified from geometrical considerations; it is proposed to employ a so-called straining correction parameter, alpha(str). Sticking efficiencies determined from field experiments were lower than those determined under laboratory conditions. We hypothesize that this is due to preferential flow mechanisms, E. coli population heterogeneity, and/or the presence of organic and inorganic compounds in wastewater possibly affecting bacterial attachment characteristics. Of equal importance is the inactivation or die-off of E. coli that is affected by factors like type of bacterial strain, temperature, predation, antagonism, light, soil type, pH, toxic substances, and dissolved oxygen. Modeling transport of E. coli can be separated into three steps: (1) attachment rate coefficients and straining rate coefficients can be calculated from Darcy flow velocity fields or pore water flow velocity fields, calculated SCCE fields, realistic sticking efficiency values and straining correction parameters, (2) together with the inactivation rate coefficient, total rate coefficient fields can be generated, and (3) used as input for modeling the transport of E. coli in existing contaminant transport codes. Areas of future research are manifold and include the effects of typical wastewater characteristics, including high concentrations of organic compounds, on the transport of E. coli and thermotolerant coliforms, and the upscaling of experiments to represent typical field conditions, possibly including preferential flow mechanisms and the aspect of population heterogeneity of E. coli.     

Transport of Escherichia coli in saturated porous media: dual mode deposition and intra-population heterogeneity

Because of heterogeneity among members of a bacteria population, deposition rates of bacteria may decrease upon the distance bacteria are transported in an aquifer. Such deposition rate decreases may result in retained bacteria concentrations, which decrease hyper-exponentially as a function of transport distance, and may therefore significantly affect the transport of colloids in aquifers. We investigated the occurrence of hyper-exponential deposition of Escherichia coli, an important indicator for fecal contamination, and the causes for such behavior. In a series of column experiments with glass beads of various sizes, we found that attachment of E. coli decreased hyper-exponentially, or, on logarithmic scale in a bimodal way, as a function of the transported distance from the column inlet. From data fitting of the retained bacteria concentration profiles, the sticking efficiency of 40% of the E. coli population was high (alpha=1), while the sticking efficiency of 60% was low (alpha=0.01). From the E. coli total population, an E. coli subpopulation consisting of slow attachers could be isolated by means of column passage. In subsequent column experiments this subpopulation attached less than the E. coli total population, consisting of both slow and fast attachers. We concluded that the main driver for the observed dual mode deposition was heterogeneity among members of the bacteria population. Intra-population may result in some microbes traveling surprisingly high distances in the subsurface. Extending the colloid filtration theory with intra-population variability may provide a valuable framework for assessing the transport of bacteria in aquifers.     

UV inactivation and characteristics after photoreactivation of Escherichia coli with plasmid: health safety concern about UV disinfection

Occurrence and degree of photoreactivation after ultraviolet (UV) exposure have been widely studied. However, the characteristics of photoreactivated microorganisms were rarely investigated. Hence, in this study, Escherichia coli with plasmids of ampicillin (amp)-resistance or fluorescence was used as indicators to examine the UV inactivation efficiencies and variations of characteristics of E. coli after subsequent photoreactivation.The experimental results indicate that the amp-resistant bacteria and the fluorescent bacteria used in this study had similar trends of UV dose-response curves. 3.5-log₁₀ and 3-log₁₀ reductions were achieved with a UV dose of 5 mJ/cm² for the amp-resistant and fluorescent E. coli, respectively. There was no significant difference in the UV inactivation behavior, as compared with common strains of E. coli.For the amp-resistant E. coli and the fluorescent E. coli, after exposures with UV doses of 5, 15, 25, 40 and 80 mJ/cm², the corresponding percent photoreactivations after a 4 h exposure to photoreactivating light were 1% and 46% respectively for a UV dose of 5 mJ/cm², and essentially negligible for all other UV doses. Furthermore, the photoreactivated amp-resistant bacteria still have the ability of amp-resistance. And the revived fluorescent E. coli showed similar fluorescent behavior, compared with the untreated bacteria. The experimental results imply that after UV inactivation and subsequent photoreactivation, the bacteria retained the initial characteristics coded in the plasmid. This reveals a possibility that some characteristics of bacteria can retain or recover through photoreactivation, and a safety concern about pathogenicity revival might need to be considered with UV disinfection and photoreactivation.     

Effects of primary sludge particulate (PSP) entrapment on ultrasonic (20 kHz) disinfection of Escherichia coli

The role of primary sludge particulates (PSPs) in ultrasonic disinfection of Escherichia coli (E. coli) was investigated. Entrapment of E. coli by PSP was directly observed through scanning electron microscope (SEM) after E. coli and PSP were incubated together in water for 24 h at 35 °C. Entrapment coefficient was proposed for the first time to reflect the ability of PSP to entrap E. coli and was estimated as 1.4 × 10³ CFU/mg PSP under our experimental conditions. Ultrasonication (20 kHz) of different E. coli-PSPs solutions showed that the entrapped E. coli cells were protected by PSP from ultrasonication and the unentrapped cells were not. However, the protection of entrapped E. coli cells gradually decreased as ultrasonication proceeded, suggesting the ability of power ultrasonication to deprotect the entrapped E. coli cells. SEM studies suggested a two-step mechanism for ultrasonic (20 kHz) disinfection of entrapped E. coli: breakdown of the protective PSP refugia and disinfection of the exposed E. coli cells. This research will enable more informed decisions about disinfection of aqueous samples where porous PSP are present.