Effect of various environmental factors on the viability of Cryptosporidium parvum oocysts

Aims: To evaluate individual and combined effects of temperature (4, 18 and 25°C), pH (7 and 10), ammonia (5 and 50 mg l^?1) and exposure time (1, 2, 4 and 6 days) on the viability of Cryptosporidium parvum oocysts in water. Methods and Results: The viability of oocysts was evaluated using the fluorogenic vital dyes assay (4′,6‐diamidino‐2‐phenylindole and propidium iodide). All the factors analysed (temperature, pH, ammonia and exposure time) and their interaction were statistically significant (P < 0·005). Exposure of oocysts to pH 10 for 6 days at 25°C reduced oocyst viability from ～80% to 51%. Similarly, the exposure of C. parvum oocysts to 5 mg NH₃ l^?1 and 50 mg NH₃ l^?1 for 4 days reduced their viability from between ～80% to 41·5% and 14·8%, respectively. Conclusions: The interaction between pH, temperature and exposure time may have adverse effects on the survival of C. parvum oocysts in water. Low concentrations of ammonia, as commonly found in alga‐based wastewater systems, over a long period of time can produce high C. parvum oocyst inactivation rates. Significance and Impact of the Study: This study provides relevant data on the inactivation of C. parvum oocysts in alga‐based wastewater‐treatment systems in the northwest of Spain.     

Chlorine Dioxide Inactivation of Cryptosporidium parvum Oocysts and Bacterial Spore Indicators

Cryptosporidium parvum, which is resistant to chlorine concentrations typically used in water treatment, is recognized as a significant waterborne pathogen. Recent studies have demonstrated that chlorine dioxide is a more efficient disinfectant than free chlorine against Cryptosporidium oocysts. It is not known, however, if oocysts from different suppliers are equally sensitive to chlorine dioxide. This study used both a most-probable-number–cell culture infectivity assay and in vitro excystation to evaluate chlorine dioxide inactivation kinetics in laboratory water at pH 8 and 21°C. The two viability methods produced significantly different results (P < 0.05). Products of disinfectant concentration and contact time (Ct values) of 1,000 mg · min/liter were needed to inactivate approximately 0.5 log₁₀ and 2.0 log₁₀ units (99% inactivation) of C. parvum as measured by in vitro excystation and cell infectivity, respectively, suggesting that excystation is not an adequate viability assay. Purified oocysts originating from three different suppliers were evaluated and showed marked differences with respect to their resistance to inactivation when using chlorine dioxide. Ct values of 75, 550, and 1,000 mg · min/liter were required to achieve approximately 2.0 log₁₀ units of inactivation with oocysts from different sources. Finally, the study compared the relationship between easily measured indicators, including Bacillus subtilis (aerobic) spores and Clostridium sporogenes (anaerobic) spores, and C. parvum oocysts. The bacterial spores were found to be more sensitive to chlorine dioxide than C. parvum oocysts and therefore could not be used as direct indicators of C. parvum inactivation for this disinfectant. In conclusion, it is suggested that future studies address issues such as oocyst purification protocols and the genetic diversity of C. parvum, since these factors might affect oocyst disinfection sensitivity.     

Mechanism of the Photocatalytic Inactivation of Lactobacillus casei Phage PL-1 by Titania Thin Film

The mechanism of the inactivation of Lactobacillus casei phage PL-1 suspended in a phosphate buffer by black-light (BL) -catalytic titanium dioxide (TiO₂) thin film was studied. Generation of both superoxide anions (O₂ ⁻) and hydroxyl radicals ( · OH) was confirmed in the aqueous medium in which TiO₂ film was settled with BL irradiation under gentle shaking. With BL-irradiation alone without TiO₂ film, only O₂ ⁻ was generated to some extent. The genome DNA inside the phage particles was found to be fragmented by the treatment of PL-1 phages with BL-catalytic TiO₂ film. The phage inactivation by BL-catalytic TiO₂ film was inhibited by the addition of albumin in a concentration-dependent manner. BL-catalytic TiO₂ film was considered to cause primarily the damage to the capsid protein through the generation of active oxygen species such as · OH, followed by damage to the genome DNA inside the phage particles. Received: 11 August 2000 / Accepted: 30 August 2000     

Chlorine dioxide inactivation of bacterial threat agents

Aims: To evaluate the efficacy of chlorine dioxide (ClO₂) against seven species of bacterial threat (BT) agents in water. Methods and Results: Two strains of Bacillus anthracis spores, Yersinia pestis, Francisella tularensis, Burkholderia pseudomallei, Burkholderia mallei and Brucella species were each inoculated into a ClO₂ solution with an initial concentration of 2·0 (spores only) and 0·25 mg l^?1 (all other bacteria) at pH 7 or 8, 5 or 25°C. At 0·25 mg l^?1 in potable water, six species were inactivated by at least three orders of magnitude within 10 min. Bacillus anthracis spores required up to 7 h at 5°C for the same inactivation with 2·0 mg l^?1 ClO₂. Conclusions: Typical ClO₂ doses used in water treatment facilities would be effective against all bacteria tested except B. anthracis spores that would require up to 7 h with the largest allowable dose of 2 mg l^?1 ClO₂. Other water treatment processes may be required in addition to ClO₂ disinfection for effective spore removal or inactivation. Significance and Impact of Study: The data obtained from this study provide valuable information for water treatment facilities and public health officials in the event that a potable water supply is contaminated with these BT agents.     

Cell Culture-Taqman PCR Assay for Evaluation of Cryptosporidium parvum Disinfection

Cryptosporidium parvum represents a challenge to the water industry and a threat to public health. In this study, we developed a cell culture-quantitative PCR assay to evaluate the inactivation of C. parvum with disinfectants. The assay was validated by using a range of disinfectants in common use in the water industry, including low-pressure UV light (LP-UV), ozone, mixed oxidants (MIOX), and chlorine. The assay was demonstrated to be reliable and sensitive, with a lower detection limit of a single infectious oocyst. Effective oocyst inactivation was achieved (>2 log₁₀ units) with LP-UV (20 mJ/cm²) or 2 mg of ozone/liter (for 10 min). MIOX and chlorine treatments of oocysts resulted in minimal effective disinfection, with <0.1 log₁₀ unit being inactivated. These results demonstrate the inability of MIOX to inactivate Cryptosporidium. The assay is a valuable tool for the evaluation of disinfection systems for drinking water and recycled water.     

Solar UV reduces Cryptosporidium parvum oocyst infectivity in environmental waters

Aims: To determine the effect of solar radiation on Cryptosporidium parvum in tap and environmental waters. Methods and Results: Outdoor tank experiments and a cell culture infectivity assay were used to measure solar inactivation of C. parvum oocysts in different waters. Experiments conducted on days with different levels of solar insolation identified rapid inactivation of oocysts in tap water (up to 90% inactivation within the first hour). Increased dissolved organic carbon content in environmental waters decreased solar inactivation. The role of solar ultraviolet (UV) in inactivation was confirmed by long-pass filter experiments, where UV-B was identified as the most germicidal wavelength. Reductions in oocyst infectivity following solar radiation were not related to a loss of excystation capacity. Conclusions: Solar UV can rapidly inactivate C. parvum in environmental waters. Significance and Impact of the Study: This is the first study to assess natural sunlight inactivation of C. parvum oocysts in surface waters and drinking water using an infectivity measure and determines the wavelengths of light responsible for the inactivation. The findings presented here provide valuable information for determining the relative risks associated with Cryptosporidium oocysts in aquatic environments and identify solar radiation as a critical process affecting the oocyst survival in the environment.     

The influence of (photo)respiration on carbon isotope discrimination in plants

The contribution which (photo)respiration makes to carbon isotope discrimination (Δ¹³C) was examined by conducting simultaneous gas exchange measurements and isotopic analysis of carbon dioxide passing over leaves of Triticum aestivum and Phaseolus vulgaris, via manipulations of the carbon isotope composition (δ¹³C) of source CO₂ during growth and measurement. Dark respiration only altered net Δ¹³C (Δ_obs) at low CO₂ assimilation, and was sensitive to source CO₂δ¹³C during measurement. Photorespiration reduced Δ_obs relative to Δ¹³C predicted from p_i/p_a (Δ_i) over the full range of CO₂ assimilation, to a greater degree under elevated oxygen partial pressure (pO₂), indicating fractionation during photorespiration (f) in T. aestivum. For P. vulgaris, Δ_obs was insensitive to elevated pO₂ at higher assimilation rates, suggesting that f was minimal. A model was developed to calculate gross discrimination (Δ_ps), independent of (photo)respiration, from which estimates of f were obtained for T. aestivum (3.3‰) and P. vulgaris (0.5‰). Because photorespiratory fractionation varies interspecifically, and influences net Δ¹³C which is directly reflected in leaf δ¹³C, consideration of (photo)respiratory fractionation is necessary when interpreting δ¹³C of leaf material, especially under conditions where (photo)respiratory CO₂ losses make a large relative contribution to total plant carbon budgets.     

C. botulinum inactivation kinetics implemented in a computational model of a high‐pressure sterilization process

High‐pressure, high‐temperature (HPHT) processing is effective for microbial spore inactivation using mild preheating, followed by rapid volumetric compression heating and cooling on pressure release, enabling much shorter processing times than conventional thermal processing for many food products. A computational thermal fluid dynamic (CTFD) model has been developed to model all processing steps, including the vertical pressure vessel, an internal polymeric carrier, and food packages in an axis‐symmetric geometry. Heat transfer and fluid dynamic equations were coupled to four selected kinetic models for the inactivation of C. botulinum; the traditional first‐order kinetic model, the Weibull model, an nth‐order model, and a combined discrete log‐linear nth‐order model. The models were solved to compare the resulting microbial inactivation distributions. The initial temperature of the system was set to 90°C and pressure was selected at 600 MPa, holding for 220 s, with a target temperature of 121°C. A representation of the extent of microbial inactivation throughout all processing steps was obtained for each microbial model. Comparison of the models showed that the conventional thermal processing kinetics (not accounting for pressure) required shorter holding times to achieve a 12D reduction of C. botulinum spores than the other models. The temperature distribution inside the vessel resulted in a more uniform inactivation distribution when using a Weibull or an nth‐order kinetics model than when using log‐linear kinetics. The CTFD platform could illustrate the inactivation extent and uniformity provided by the microbial models. The platform is expected to be useful to evaluate models fitted into new C. botulinum inactivation data at varying conditions of pressure and temperature, as an aid for regulatory filing of the technology as well as in process and equipment design. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Inactivation of Escherichia coli by citral

Aims: The aim was to evaluate (i) the resistance of Escherichia coli BJ4 to citral in a buffer system as a function of citral concentration, treatment medium pH, storage time and initial inoculum size, (ii) the role of the sigma factor RpoS on citral resistance of E. coli, (iii) the role of the cell envelope damage in the mechanism of microbial inactivation by citral and (iiii) possible synergistic effects of mild heat treatment and pulsed electric fields (PEF) treatment combined with citral. Methods and Results: The initial inoculum size greatly affected the efficacy of citral against E. coli cells. Exposure to 200 μl l^?1 of citral at pH 4·0 for 24 h at 20°C caused the inactivation of more than 5 log₁₀ cycles of cells starting at an inoculum size of 10⁶ or 10⁷ CFU ml^?1, whereas increasing the cell concentration to 10⁹ CFU ml^?1 caused <1 log₁₀ cycle of inactivation. Escherichia coli showed higher resistance to citral at pH 4·0 than pH 7·0. The rpoS null mutant strain E. coli BJ4L1 was less resistant to citral than the wild‐type strain. Occurrence of sublethal injury to both the cytoplasmic and outer membranes was demonstrated by adding sodium chloride or bile salts to the recovery media. The majority of sublethally injured cells by citral required energy and lipid synthesis for repair. A strongly synergistic lethal effect was shown by mild heat treatment combined with citral but the presence of citral during the application of a PEF treatment did not show any advantage. Conclusions: This work confirms that cell envelope damage is an important event in citral inactivation of bacteria, and it describes the key factors on the inactivation of E. coli cells by citral. Significance and Impact of the Study: Knowledge about the mechanism of microbial inactivation by citral helps establish successful combined preservation treatments.     

The development of Escherichia coli and Listeria monocytogenes variants resistant to high‐pressure carbon dioxide inactivation

Aims: The objective of this study was to investigate whether bacterial cells could develop resistance (as a part of their adaptation strategy) to high‐pressure CO₂ (HPCD) inactivation. Methods and Results: Alternating cycles of exposure to pressurized CO₂ (10·5 MPa, 35°C, 400 min^?1, 70% working volume ratio during 10 min) and re‐growth of the surviving subpopulation were used to investigate possible increases in the resistance of Escherichia coli and Listeria monocytogenes to HPCD. The results show an increased resistance of both pathogens tested after seven cycles of inactivation. Increase in the resistance after 15 cycles resulted in a difference of 2·4 log CFU ml^?1 in log N₀/N_i when parental (N₀) and treated cultures (N_i) of E. coli and L. monocytogenes were compared. Conclusions: Current findings indicate the ability of micro‐organisms to adapt to HPCD preservation technology. Significance and Impact of the Study: The occurrence of HPCD‐resistant micro‐organisms could pose a new hazard to the safety and stability of HPCD‐processed foods.     

Low-Pressure UV Inactivation and DNA Repair Potential of Cryptosporidium parvum Oocysts

Because Cryptosporidium parvum oocysts are very resistant to conventional water treatment processes, including chemical disinfection, we determined the kinetics and extent of their inactivation by monochromatic, low-pressure (LP), mercury vapor lamp UV radiation and their subsequent potential for DNA repair of UV damage. A UV collimated-beam apparatus was used to expose suspensions of purified C. parvum oocysts in phosphate-buffered saline, pH 7.3, at 25°C to various doses of monochromatic LP UV. C. parvum infectivity reductions were rapid, approximately first order, and at a dose of 3 mJ/cm² (=30 J/m²), the reduction reached the cell culture assay detection limit of ~3 log₁₀. At UV doses of 1.2 and 3 mJ/cm², the log₁₀ reductions of C. parvum oocyst infectivity were not significantly different for control oocysts and those exposed to dark or light repair conditions for UV-induced DNA damage. These results indicate that C. parvum oocysts are very sensitive to inactivation by low doses of monochromatic LP UV radiation and that there is no phenotypic evidence of either light or dark repair of UV-induced DNA damage.     

Cold hardiness and sugar content in photo‐insensitive individuals of the cotton bollworm Helicoverpa armigera

Abstract A proportion of Helicoverpa armigera collected from fields in Okayama Prefecture (Western Japan; 34.6°N, 134.1°E) does not enter diapause when reared under a short days at 20 °C during the larval stages. However, diapause in such photo‐insensitive individuals can be induced when they are reared at moderately low temperatures, such as 15 °C, regardless of photoperiod. To determine whether such photo‐insensitive individuals can survive overwintering in fields, the present study compares the cold hardiness and sugar content between nondiapausing and diapausing pupae of photo‐insensitive individuals selected over several generations at 20 °C under a short day photoperiod (LD 10 : 14 h). Diapausing and nondiapausing pupae are obtained under the short days by rearing at 15 and 20 °C, respectively, during larval and pupal stages. These pupae are stepwise acclimated at a reduction of 5 °C every 5 days to 0 °C. Maximum survival periods of nondiapausing and diapausing pupae at 0 °C are approximately 30 and 90 days, respectively. Trehalose content in diapausing pupae increases, reaches a maximum level (1.95 mg 100 mg^?1 in males and 2.1 mg 100 mg^?1 in females) 28 days after exposure to 0 °C and then decreases. On the other hand, glucose content in diapausing pupae increases (maximum level: 0.32 mg 100 mg^?1 in males and 0.21 mg 100 mg^?1 in females) with decreasing trehalose content 42 days after exposure to 0°C. The decrease in trehalose content and the increase in glucose content may be linked to termination of diapause in H. armigera. These results suggest that, in Japan, the photo‐insensitive individuals can only survive in the mild winters of southern regions, and not in the severe winters of northern regions.     

Linking microbial activity and soil organic matter transformations in forest soils under elevated CO2

Soil organic matter (SOM) dynamics ultimately govern the ability of soil to provide long‐term C sequestration and the nutrients required for ecosystem productivity. Predicting belowground responses to elevated CO₂ requires an integrated understanding of SOM transformations and the microbial activity that governs them. It remains unclear how the microorganisms upon which these transformations depend will function in an elevated CO₂ world. This study examines SOM transformations and microbial metabolism in soils from the Duke Free Air Carbon Enrichment site in North Carolina, USA. We assessed microbial respiration and net nitrogen (N) mineralization in soils with and without elevated CO₂ exposure during a 100‐day incubation. We also traced the depleted C isotopic signature of the supplemental CO₂ into SOM and the soils' phospholipid fatty acids (PLFA), which serve as biomarkers for living cells. Cumulative net N mineralization in elevated CO₂ soils was 50% that in control soils after a 100‐day incubation. Respiration was not altered with elevated CO₂. C : N ratios of bulk SOM did not change with elevated CO₂, but incubation data suggest that the C : N ratios of mineralized organic matter increased with elevated CO₂. Values of SOM δ¹³C were depleted with elevated CO₂ (?26.7±0.2 vs. ?30.2±0.3‰), reflecting the depleted signature of the supplemental CO₂. We compared δ¹³C of individual PLFA with the δ¹³C of SOM to discern incorporation of the depleted C isotopic signature into soil microbial groups in elevated CO₂ plots. PLFA i15:0, a15:0, and 10Met18:0 reflected significant incorporation of recently produced photosynthate, suggesting that the bacterial groups defined by these biomarkers are active metabolizers in elevated CO₂ soils. At least one of these groups (actinomycetes, 10Met18:0) specializes in metabolizing less labile substrates. Because control plots did not receive an equivalent ¹³C tracer, we cannot determine from these data whether this group of organisms was stimulated by elevated CO₂ compared with these organisms in control soils. Stimulation of this group, if it occurred in the elevated CO₂ plot, would be consistent with a decline in the availability of mineralizable organic matter with elevated CO₂, which incubation data suggest may be the case in these soils.     

Different Inactivation Behaviors of MS-2 Phage and Escherichia coli in TiO2 Photocatalytic Disinfection

Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO₂ photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (·OH), which is generated on the surface of UV-illuminated TiO₂, plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H₂O₂ and O₂·⁻, etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusion-limited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe²⁺, were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O₂·⁻ and H₂O₂, according to the present results.     

Reduction of Escherichia coli O157:H7 on radish seeds by sequential application of aqueous chlorine dioxide and dry‐heat treatment

Aims: To assess the effectiveness of sequential treatments of radish seeds with aqueous chlorine dioxide (ClO₂) and dry heat in reducing the number of Escherichia coli O157:H7. Methods and Results: Radish seeds containing E. coli O157:H7 at 5·5 log CFU g^?1 were treated with 500 μg ml^?1 ClO₂ for 5 min and subsequently heated at 60°C and 23% relative humidity for up to 48 h. Escherichia coli O157:H7 decreased by more than 4·8 log CFU g^?1 after 12 h dry‐heat treatment. The pathogen was inactivated after 48 h dry‐heat treatment, but the germination rate of treated seeds was substantially reduced from 91·2 ± 5·0% to 68·7 ± 12·3%. Conclusions: Escherichia coli O157:H7 on radish seeds can be effectively reduced by sequential treatments with ClO₂ and dry heat. To eliminate E. coli O157:H7 on radish seeds without decreasing the germination rate, partial drying of seeds at ambient temperature before dry‐heat treatment should be investigated, and conditions for drying and dry‐heat treatment should be optimized. Significance and Impact of the study: This study showed that sequential treatment with ClO₂ and dry‐heat was effective in inactivating large numbers of E. coli O157:H7 on radish seeds. These findings will be useful when developing sanitizing strategies for seeds without compromising germination rates.     

Titanium dioxide induced cell damage: A proposed role of the carboxyl radical

Titanium dioxide (TiO₂) nanoparticles have been shown to be genotoxic to cells exposed to ultraviolet A (UVA) radiation. Using the technique of electron spin resonance (ESR) spin trapping, we have confirmed that the primary damaging species produced on irradiation of TiO₂ nanoparticles is the hydroxyl (OH) radical. We have applied this technique to TiO₂-treated fish and mammalian cells under in vitro conditions and observed the additional formation of carboxyl radical anions (CO₂^?) and superoxide radical anions (O₂^?). This novel finding suggests a hitherto unreported pathway for damage, involving primary generation of OH radicals in the cytoplasm, which react to give CO₂^? radicals. The latter may then react with cellular oxygen to form O₂^? and genotoxic hydrogen peroxide (H₂O₂).     

Facile and Efficient Atomic Hydrogenation Enabled Black TiO2 with Enhanced Photo‐Electrochemical Activity via a Favorably Low‐Energy‐Barrier Pathway

Black TiO₂ has demonstrated a great potential for a variety of renewable energy technologies. However, its practical application is heavily hindered due to lack of efficient hydrogenation methods and a deeper understanding of hydrogenation mechanisms. Here, a simple and straightforward hot wire annealing (HWA) method is presented to prepare black TiO₂ (H–TiO₂) nanorods with enhanced photo‐electrochemical (PEC) activity by means of atomic hydrogen [H]. Compared to conventional molecular hydrogen approaches, the HWA shows remarkable effectiveness without any detrimental side effects on the device structure, and simultaneously the photocurrent density of H–TiO₂ reaches 2.5 mA cm^?2 (at 1.23 V vs reversible hydrogen electrode (RHE)). Due to the controllable and reproducible [H] flux, the HWA can be developed as a standard hydrogenation method for black TiO₂. Meanwhile, the relationships between the wire temperatures, structural, optical, and photo‐electrochemical properties are systematically investigated to verify the improved PEC activity. Furthermore, the density functional theory (DFT) study provides a comprehensive insight not only into the highly efficient mechanism of the HWA approach but also its favorably low‐energy‐barrier hydrogenation pathway. The findings will have a profound impact on the broad energy applications of H–TiO₂ and contribute to the fundamental understanding of its hydrogenation.     

Temperature-assisted high hydrostatic pressure inactivation of Staphylococcus aureus in a ham model system: evaluation in selective and nonselective medium

Aims: The purpose of this study was to investigate the inactivation kinetics of Staphylococcus aureus in a ham model system by high hydrostatic pressure at ambient (25°C) and selected temperatures (45, 55°C). Selective [Baird Parker (BP) agar] and nonselective [brain heart infusion (BHI) agar] growth media were used for enumeration in order to count viable and sublethally injured cells. Methods and Results: The micro‐organism was exposed to a range of pressures (450, 500, 550, 600 MPa) at ambient temperature (25°C) for up to 45 min. Additionally, the behaviour of the micro‐organism was evaluated at mild temperatures in combination with high pressure treatment, namely: (i) 350, 400 and 450 MPa at 45°C; and (ii) 350 and 400 MPa at 55°C, for up to 12 min. Inactivation kinetics were calculated in terms of D_p and z_p values. Survival curves of S. aureus at ambient temperature were mostly linear, whereas when temperature was applied, tailing was observed in most survival curves. The estimated D_p values and therefore the number of surviving cells, were substantially higher on the selective BP agar in the whole range of pressures applied, indicating that S. aureus showed greater recovery in the selective BP agar than the nonselective BHI agar. Samples pressurized at ambient temperature needed higher pressures (over 500 MPa) to achieve a reduction of the population of the pathogen more than 5 log CFU ml^?1. The same level of inactivation was achieved at lower pressure levels when mild heating was simultaneously applied. Indeed, more than 6 log CFU ml^?1 reductions were obtained at 400 MPa and 55°C within the first 7 min of the process in BHI medium. Conclusion: Elevated temperatures allowed lower pressure levels and shorter processing times of pathogen inactivation than at room temperature. Greater recovery of the pathogen was observed in the selective (BP agar) medium, regardless of pressure and temperature applied. Significance and Impact of the Study: The obtained kinetics could be employed by the industry in selecting optimum pressure/temperature processing conditions. Attention must be given to the selection of the enumeration medium, as the use of an inappropriate medium would lead to underestimation of the surviving cells, thus imposing a risk in the microbiological safety of the product.     

Computational modeling of the adsorption and •OH initiated photochemical and photocatalytic primary oxidation of nitrobenzene

The adsorption and primary oxidation step for the photodegradation of nitrobenzene (NB) have been studied computationally using MSINDO SCF MO method. The method performs efficiently for extended surface models such as Ti₃₆O₉₀H₃₆. Molecular dynamics simulations have revealed that NB is linked to TiO₂ surface at the titanium ion via the oxygen atoms of NO₂ group. In addition, the computed vibrational density of states for the adsorbed NB molecule is in reasonably good agreement with the available experimental data and theoretical results. In order to identify the primary photochemical and photocatalytic ^•OH initiated photooxidation intermediates, we have employed two different theoretical approaches, frontier orbital theory and Wheland localization theory. It has been found that the meta- hydroxynitrocyclohexadienyl radical is energetically more favored than para- and ortho-hydroxynitrocyclohexadienyl radicals for the photochemical photolysis, whereas in the case of photocatalysis, the ^•OH radical attack is unselective and all three possible isomers have comparable stabilities. Figure Minimum energy adsorption conformation of nitrobenzene onto TiO₂ (100) surface     

Chlorine disinfection of Francisella tularensis

Aims: To determine the range of free available chlorine (FAC) required for disinfection of the live vaccine strain (LVS) and wild‐type strains of Francisella tularensis. Methods and Results: Seven strains of planktonic F. tularensis were exposed to 0·5 mg·l^?1 FAC for two pH values, 7 and 8, at 5 and 25°C. LVS was inactivated 2 to 4 times more quickly than any of the wild‐type F. tularensis strains at pH 8 and 5°C. Conclusions: Free available chlorine residual concentrations routinely maintained in drinking water distribution systems would require up to two hours to reduce all F. tularensis strains by 4 log₁₀. LVS was inactivated most quickly of the tested strains. Significance and Impact of the Study: This work provides contact time (CT) values that are useful for drinking water risk assessment and also suggests that LVS may not be a good surrogate in disinfection studies.