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.     

Inactivation of murine norovirus, feline calicivirus and echovirus 12 as surrogates for human norovirus (NoV) and coliphage (F+) MS2 by ultraviolet light (254 nm) and the effect of cell association on UV inactivation

Aims: To determine inactivation profiles of three human norovirus (NoV) surrogate viruses and coliphage MS2 by ultraviolet (UV) irradiation and the protective effect of cell association on UV inactivation. Methods and Results: The inactivation rate for cell‐free virus or intracellular echovirus 12 was determined by exposure to 254‐nm UV light at fluence up to 100 mJ cm^?2. The infectivity of murine norovirus (MNV), feline calicivirus (FCV) and echovirus 12 was determined by cell culture infectivity in susceptible host cell lines, and MS2 infectivity was plaque assayed on Escherichia coli host cells. The UV fluencies to achieve 4‐log₁₀ inactivation were 25, 29, 30 and 70 (mJ cm^?2) for cell‐free FCV, MNV, echovirus 12 and MS2, respectively. However, a UV fluence of 85 mJ cm^?2 was needed to inactivate intracellular echovirus 12 by 4 log₁₀. Conclusions: Murine norovirus and echoviruses 12 are more conservative surrogates than FCV to predict the UV inactivation response of human NoV. Intracellular echovirus 12 was 2·8‐fold more resistant to UV irradiation than cell‐free one. Significance and Impact of the Study: Variation in UV susceptibilities among NoV surrogate viruses and a likely protective effect of cell association on virus susceptibility to UV irradiation should be considered for effective control of human NoV in water.     

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.     

Efficacy of alcohol-based hand sanitizers against human norovirus using RNase-RT-qPCR with validation by human intestinal enteroid replication

Successful human norovirus (HuNoV) cultivation in stem cell-derived human intestinal enteroids (HIE) was recently reported. The purpose of this study was to evaluate the anti-HuNoV efficacy of two alcohol-based commercial hand sanitizers and 60% ethanol by suspension assay using RNase-RT-qPCR, with subsequent validation of efficacy by HuNoV cultivation using the HIE model. In suspension, when evaluated by RNase-RT-qPCR, 60% ethanol resulted in less than one log₁₀ reduction in HuNoV genome equivalent copies (GEC) regardless of contact time (30 or 60s) or soil load. The two commercial products outperformed 60% ethanol regardless of contact time or soil load, providing 2·2–3·2 log₁₀ HuNoV GEC reductions by suspension assay. Product B could not be validated in the HIE model due to cytotoxicity. Following a 60s exposure, viral replication in the HIE model increased 1·9 ± 0·2 log₁₀ HuNoV GEC for the neutralization (positive) control and increased 0·9 ± 0·2 log₁₀ HuNoV GEC in challenged HIE after treatment with 60% ethanol. No HuNoV replication in HIE was observed after a 60 s exposure to Product A.     

Validation of SYTO 9/Propidium Iodide Uptake for Rapid Detection of Viable but Noncultivable <Emphasis Type="Italic">Legionella pneumophila</Emphasis>

Legionella pneumophila is an ubiquitous environmental microorganism that can cause Legionnaires’ disease or Pontiac fever. As a waterborne pathogen, it has been found to be resistant to chlorine disinfection and survive in drinking water systems, leading to potential outbreaks of waterborne disease. In this work, the effect of different concentrations of free chlorine was studied (0.2, 0.7, and 1.2 mg l^?1), the cultivability of cells assessed by standard culture techniques (buffered charcoal yeast extract agar plates) and viability using the SYTO 9/propidium iodide fluorochrome uptake assay (LIVE/DEAD® BacLight?). Results demonstrate that L. pneumophila loses cultivability after exposure for 30 min to 0.7 mg l^?1 of free chlorine and in 10 min when the concentration is increased to 1.2 mg l^?1. However, the viability of the cells was only slightly affected even after 30 min exposure to the highest concentration of chlorine; good correlation was obtained between the rapid SYTO 9/propidium iodide fluorochrome uptake assay and a longer cocultivation with Acanthamoeba polyphaga assay, confirming that these cells could still recover their cultivability. These results raise new concerns about the assessment of drinking water disinfection efficiency and indicate the necessity of further developing new validated rapid methods, such as the SYTO 9/propidium iodide uptake assay, to assess viable but noncultivable L. pneumophila cells in the environment.     

Effects of Source Water Quality on Chlorine Inactivation of Adenovirus,Coxsackievirus, Echovirus,and Murine Norovirus

More information is needed on the disinfection efficacy of chlorine for viruses in source water. In this study, chlorine disinfection efficacy was investigated for USEPA Contaminant Candidate List viruses coxsackievirus B5 (CVB5), echovirus 1 (E1), murine norovirus (MNV), and human adenovirus 2 (HAdV2) in one untreated groundwater source and two partially treated surface waters. Disinfection experiments using pH 7 and 8 source water were carried out in duplicate, using 0.2 and 1 mg/liter free chlorine at 5 and 15°C. The efficiency factor Hom (EFH) model was used to calculate disinfectant concentration × contact time (CT) values (mg·min/liter) required to achieve 2-, 3-, and 4-log₁₀ reductions in viral titers. In all water types, chlorine disinfection was most effective for MNV, with 3-log₁₀ CT values at 5°C ranging from ≤0.020 to 0.034. Chlorine disinfection was least effective for CVB5 in all water types, with 3-log₁₀ CT values at 5°C ranging from 2.3 to 7.9. Overall, disinfection proceeded faster at 15°C and pH 7 for all water types. Inactivation of the study viruses was significantly different between water types, but no single source water had consistently different inactivation rates than another. CT values for CVB5 in one type of source water exceeded the recommended CT values set forth by USEPA''s Guidance Manual for Compliance with the Filtration and Disinfection Requirements for Public Water Systems using Surface Water Sources. The results of this study demonstrate that water quality plays a substantial role in the inactivation of viruses and should be considered when developing chlorination plans.Disinfection processes are critical for the reduction of infectious virus concentrations in source water, because viruses are less efficiently removed by primary treatment of drinking water (e.g., coagulation and filtration) than are other pathogen types of concern (e.g., bacteria and protozoa). Over the years, many disinfection studies have focused on the inactivation of viruses in purified and buffered, demand-free, reagent-grade water (RGW). However, relatively few investigators have examined the impact of water quality during the disinfection process, even though water quality has been found to be a significant factor for inactivation of viruses.Several researchers found that the inactivation rate of poliovirus by free chlorine increased as the ionic concentration of water increased. In one study, poliovirus 1 was inactivated three times faster in boric acid buffer than in purified water (3). In addition, several investigators found that when the ionic content of buffered water was raised by the addition of NaCl or KCl, poliovirus 1 was inactivated two to four times faster than in the buffered water alone (2, 16, 17). In another study, poliovirus 1 was inactivated 10 times more rapidly in drinking water than in purified water (4).Studies conducted with natural waters have demonstrated both increased and decreased disinfection efficacy of chlorine in these waters compared to purified or buffered waters. In a study comparing chlorine disinfection in purified water and Potomac estuarine water, coxsackievirus A9 was inactivated more rapidly in the source water. The remaining study viruses (coxsackievirus B1, echovirus 7, adenovirus 3, poliovirus 1, and reovirus 3) were all inactivated more slowly in the source water (13). Bacteriophage MS2 was inactivated more slowly by free chlorine in two types of surface water than in buffered, demand-free water. However, there was no difference between the inactivation rates of this virus in the buffered water and groundwater (10). In another study, both feline calicivirus and adenovirus 40 were inactivated more slowly in treated groundwater than in buffered, demand-free water (21).The United States Environmental Protection Agency''s (USEPA) Guidance Manual for Compliance with the Filtration and Disinfection Requirements for Public Water Systems using Surface Water Sources (Guidance Manual) recommends disinfectant concentration × contact time (CT) values of 4, 6, and 8 to achieve 2-, 3-, and 4-log₁₀ inactivation, respectively, with chlorine at 5°C and pH 6 to 9 (23). These CT values, which incorporate a safety factor of 3, were obtained from inactivation experiments conducted with monodispersed hepatitis A virus (HAV) in buffered, demand-free water. As water quality can significantly affect the disinfection efficacy of chlorine, it is unclear whether these CT value recommendations are sufficient for inactivation of viruses in source water. More information is needed to systematically examine the role of water quality in chlorine disinfection of viruses.The objective of the present study was to examine the disinfection efficacy of free chlorine on selected viruses from USEPA''s Contaminant Candidate List (CCL) (22) in one untreated and two partially treated source waters from distinct geographical regions. By comparing the efficacy of chlorine disinfection in the source water types to disinfection in buffered, chlorine-demand-free RGW (7), the impact of water quality could be examined. The four representative CCL viruses selected for this study included human adenovirus 2 (HAdV2), echovirus 1 (E1), coxsackievirus B5 (CVB5), and murine norovirus (MNV), a surrogate for human norovirus (22). The viruses were selected because they were previously found to be the least effectively inactivated viruses of their type in RGW (6). Disinfection experiments were carried out in duplicate in pH 7 and 8 source water at 5 and 15°C using 0.2 and 1 mg/liter free chlorine. Inactivation curves were plotted using Microsoft Excel, and CT values were calculated using the efficiency factor Hom (EFH) model (9).     

Assessment of adenovirus,hepatitis A virus and rotavirus presence in environmental samples in Florianopolis,South Brazil

Aims: To assess the presence of human adenovirus (HAdV), hepatitis A (HAV) virus and rotavirus A (RV‐A) in environmental samples from the Southern region of Brazil and to provide viral contamination data for further epidemiological studies and governmental actions. Methods and Results: Water samples from various sources (seawater, lagoon brackish water, urban wastewater, drinking water sources‐with and without chlorination and water derived from a polluted creek) and oysters of two growing areas were analysed by enzymatic amplification (nested PCR and RT‐PCR), quantification of HAdV genome (qPCR) and viral viability assay by integrated cell culture‐PCR (ICC‐PCR). From June 2007 to May 2008 in a total of 84 water samples, 54 (64·2%) were positive for HAdV, 16 (19%) for RV‐A and 7 (8·3%) for HAV. Viability assays showed nonpositive samples for HAV; though, infectious viruses were confirmed for RV‐A (12·5%) and HAdV (88·8%). Oyster samples by PCR were positive for HAdV (87·5%) and RV‐A (8·3%), but none for HAV. Quantitative PCR in oysters showed means loads in genomic copies (gc) of 9·1 × 10⁴ gc g^?1 (oyster farm south) and 1·5 × 10⁵ gc g^?1 (oyster farm north) and in waters ranging from 2·16 × 10⁶ (lagoon water) to 1·33 × 10⁷ gc l^?1 (untreated drinking water). Conclusions: This study has shown a widespread distribution of the analysed viruses in this particular region with high loads of HAdV in the environment which suggests the relevance of evaluating these viruses as positive indicators of viral contamination of water. Significance and Impact of the Study: The environmental approach in this study provides data concerning the prevalence, viability and quantification of enteric viruses in environmental waters and oysters in the South region of Brazil and has indicated that their presence might pose a risk to population in contact with the environmental samples searched.     

Influence of surface copper content on Stenotrophomonas maltophilia biofilm control using chlorine and mechanical stress

Abstract

This work aimed to evaluate the action of materials with different copper content (0, 57, 96 and 100%) on biofilm formation and control by chlorination and mechanical stress. Stenotrophomonas maltophilia isolated from drinking water was used as a model microorganism and biofilms were developed in a rotating cylinder reactor using realism-based shear stress conditions. Biofilms were characterized phenotypically and exposed to three control strategies: 10?mg l^?1 of free chlorine for 10?min, an increased shear stress (a fluid velocity of 1.5?m s^?1 for 30s), and a combination of both treatments. These shock treatments were not effective in biofilm control. The benefits from the use of copper surfaces was found essentially in reducing the numbers of non-damaged cells. Copper materials demonstrated better performance in biofilm prevention than chlorine. In general, copper alloys may have a positive public health impact by reducing the number of non-damaged cells in the water delivered after chlorine exposure.     

Effects of Assimilable Organic Carbon and Free Chlorine on Bacterial Growth in Drinking Water

Assimilable organic carbon (AOC) is one of the most important factors affecting the re-growth of microorganisms in drinking water. High AOC concentrations result in biological instability, but disinfection kills microbes to ensure the safety of drinking water. Free chlorine is an important oxidizing agent used during the disinfection process. Therefore, we explored the combined effects of AOC and free chlorine on bacterial growth in drinking water using flow cytometry (FCM). The initial AOC concentration was 168 μg.L^-1 in all water samples. Without free chlorine, the concentrations of intact bacteria increased but the level of AOC decreased. The addition of sodium hypochlorite caused an increase and fluctuation in AOC due to the oxidation of organic carbon. The concentrations of intact bacteria decreased from 1.1×10⁵ cells.mL^-1 to 2.6×10⁴ cells.mL^-1 at an initial free chlorine dose of 0.6 mg.L^-1 to 4.8×10⁴ cells.mL^-1 at an initial free chlorine dose of 0.3 mg.L^-1 due to free chlorine originating from sodium hypochlorite. Additionally, free chlorine might be more obviously affected AOC concentrations than microbial growth did. These results suggested that AOC and free chlorine might have combined effects on microbial growth. In this study, our results showed concentrations determined by FCM were higher than those by HPC, which indicated that some E. coli detected by FCM might not be detected using HPC in drinking water. The level of free chlorine might restrain the consumption of AOC by inhibiting the growth of E. coli; on the other hand, chlorination might increase the level of AOC, thereby increase the potential for microbial growth in the drinking water network.     

Drinking water chlorination in dairy beef fattening bulls: water quality,potential hazards,apparent total tract digestibility,and growth performance

The first study aimed to evaluate the effect of drinking water disinfection (chlorination: NaClO 15%) and conditioning (acidification: H₃PO₄ diluted 1:5 in water) on water quality, water and feed consumption, apparent total tract digestibility, and its potential hazardous effects on Holstein bulls fed high-concentrate diets. Twenty-four animals (221 ± 20.9 kg of BW, and 184 ± 9.9 days of age) were individually assigned to one of four treatments according to a 2 × 2 factorial arrangement: conditioning (with or without acidification) and disinfection (with or without chlorination). The entire study lasted 210 days. Physicochemical and microbiological water quality, water and feed consumption, haematological and biochemical blood parameters, and apparent total tract digestibility were measured; data were analysed via a mixed-effects model. Chlorination and acidification increased (P = 0.02) free residual chlorine in water, and chlorination reduced (P = 0.01) total coliform and Clostridium perfringens counts in water. Treatment did not affect water consumption, total DM intake, or blood parameters. At the beginning of the study, NDF digestibility decreased (P = 0.04) with acidification, however, this was restored at the end of the study. The second study evaluated the potential benefit of drinking water chlorination and acidification on the performance of crossbred Holstein bulls fed high-concentrate diets under commercial conditions. Ninety-six animals (322 ± 35.0 kg of BW, and 220 ± 14.2 days of age) were allocated into six pens assigned to one of the two treatments: untreated drinking water or drinking water treated with chlorination and acidification for a total of 112 days. Physicochemical and microbiological water quality, water and concentrate consumption, eating behaviour, growth performance, and carcass quality were analysed via a mixed-effects model. Water conditioning and disinfection increased (P = 0.01) free residual chlorine concentration and reduced (P = 0.04) total coliform count in water. Although water consumption and eating behaviour were similar between treatments, water conditioning and disinfection increased average daily weight gain (P = 0.03), BW before slaughter (P = 0.01), and hot carcass weight (P = 0.01). In conclusion, drinking water chlorination and acidification in fattening dairy beef bulls is recommended as it improves growth performance without any detrimental side effects on health or nutrient digestibility.     

In vivo comparison of two human norovirus surrogates for testing ethanol-based handrubs: the mouse chasing the cat!

Human noroviruses (HuNoV), a major cause of acute gastroenteritis worldwide, cannot be readily cultured in the lab. Therefore, a feline calicivirus (FCV) is often used as its surrogate to, among other things, test alcohol-based handrubs (ABHR). The more recent laboratory culture of a mouse norovirus (MNV) provides an alternative. While MNV is closer to HuNoV in several respects, to date, no comparative testing of FCV and MNV survival and inactivation on human hands has been performed. This study was designed to address the knowledge gap. The rates of loss in viability during drying on hands were −1.91 and −1.65% per minute for FCV and MNV, respectively. When the contaminated skin was exposed for 20 s to either a commercial ABHR with 62% (v/v) ethanol or to 75% (v/v) ethanol in water, FCV infectivity was reduced by <1 log₁₀ while that of MNV by nearly 2.8 log₁₀. Extending the contact time to 30 s reduced the FCV titer by almost 2 log₁₀ by both test substances and that of MNV by >3.5 log₁₀ by the commercial ABHR while 75% ethanol did not show any noticeable improvement in activity as compared to the 20 s contact. An 80% (v/v) aqueous solution of ethanol gave only a 1.75 log₁₀ reduction in MNV activity after 20 s. The results show significant differences in the ethanol susceptibility of FCV and MNV in contact times relevant to field use of ABHR and also that 62% ethanol was a more effective virucide than either 75% or 80% ethanol. These findings indicate the need for a review of the continuing use of FCV as a surrogate for HuNoV.     

Legionella in industrial cooling towers: monitoring and control strategies

Aims: Legionella contamination of industrial cooling towers has been identified as the cause of sporadic cases and outbreaks of legionellosis among people living nearby. To evaluate and control Legionella contamination in industrial cooling tower water, microbiological monitoring was carried out to determine the effectiveness of the following different disinfection treatments: (i) continuous chlorine concentration of 0·01 ppm and monthly chlorine shock dosing (5 ppm) on a single cooling tower; (ii) continuous chlorine concentration of 0·4 ppm and monthly shock of biocide P3 FERROCID 8580 (BKG Water Solution) on seven towers. Methods and Results: Legionella spp. and total bacterial count (TBC) were determined 3 days before and after each shock dose. Both strategies demonstrated that when chlorine was maintained at low levels, the Legionella count grew to levels above 10⁴ CFU l^?1 while TBC still remained above 10⁸ CFU l^?1. Chlorine shock dosing was able to eliminate bacterial contamination, but only for 10–15 days. Biocide shock dosing was also insufficient to control the problem when the disinfectant concentration was administered at only one point in the plant and at the concentration of 30 ppm. On the other hand, when at a biocide concentration of 30 or 50 ppm was distributed throughout a number of points, depending on the plant hydrodynamics, Legionella counts decreased significantly and often remained below the warning limit. Moreover, the contamination of water entering the plant and the presence of sediment were also important factors for Legionella growth. Conclusions: For effective decontamination of outdoor industrial cooling towers, disinfectants should be distributed in a targeted way, taking into account the possible sources of contamination. Significance and Impact of the Study: The data of the research permitted to modify the procedure of disinfection for better reduce the water and aerosol contamination and consequently the exposure risk.     

Inactivation of Adenoviruses,Enteroviruses, and Murine Norovirus in Water by Free Chlorine and Monochloramine

Inactivation of infectious viruses during drinking water treatment is usually achieved with free chlorine. Many drinking water utilities in the United States now use monochloramine as a secondary disinfectant to minimize disinfectant by-product formation and biofilm growth. The inactivation of human adenoviruses 2, 40, and 41 (HAdV2, HAdV40, and HAdV41), coxsackieviruses B3 and B5 (CVB3 and CVB5), echoviruses 1 and 11 (E1 and E11), and murine norovirus (MNV) are compared in this study. Experiments were performed with 0.2 mg of free chlorine or 1 mg of monochloramine/liter at pH 7 and 8 in buffered reagent-grade water at 5°C. CT values (disinfectant concentration × time) for 2- to 4-log₁₀ (99 to 99.99%) reductions in virus titers were calculated by using the efficiency factor Hom model. The enteroviruses required the longest times for chlorine inactivation and MNV the least time. CVB5 required the longest exposure time, with CT values of 7.4 and 10 mg·min/liter (pH 7 and 8) for 4-log₁₀ inactivation. Monochloramine disinfection was most effective for E1 (CT values ranged from 8 to 18 mg·min/liter for 2- and 3-log₁₀ reductions, respectively). E11 and HAdV2 were the least susceptible to monochloramine disinfection (CT values of 1,300 and 1,600 mg-min/liter for 3-log₁₀ reductions, respectively). Monochloramine inactivation was most successful for the adenoviruses, CVB5, and E1 at pH 7. A greater variation in inactivation rates between viruses was observed during monochloramine disinfection than during chlorine disinfection. These data will be useful in drinking water risk assessment studies and disinfection system planning.Disinfection is a critical step in the drinking water treatment process to inactivate infectious viruses because primary treatment is less effective for the removal of viruses. Chlorine and monochloramine are the most widely used disinfectants in the United States (2). Free chlorine is widely used as a primary disinfectant following filtration and also as a secondary disinfectant in distribution systems. Under the Long Term 2 Enhanced Surface Water Treatment Rule (38), monochloramine can also be used as a primary disinfectant, but because it requires longer contact times to achieve the same level of disinfection as free chlorine it is primarily used as a secondary disinfectant to maintain a stable disinfectant residual in the distribution system and minimize disinfection by-product formation and biofilm growth.The efficacy of chlorine disinfection for viruses has been evaluated in numerous studies over the years. Many early studies focused on the disinfection of polioviruses by chlorine (14, 17, 26, 28, 30, 39, 40, 43). Early investigators suggested a number of variables that must be controlled in the disinfection of viruses: contact time, temperature, ionic strength, pH, chlorine concentration, and virus aggregation (29, 30). These researchers concluded that comparisons and general trends of disinfection efficacy can only be discerned for viruses when the same disinfection parameters are applied.Fewer studies have investigated the disinfection efficacy of monochloramine, but monochloramine disinfection has been found to be less effective than free chlorine for viruses. In comparative studies of chlorine and monochloramine disinfection, coxsackievirus B5, adenovirus 2, and adenovirus 41 were found to be inactivated far more readily by chlorine than monochloramine (4, 5, 32). For drinking water treatment systems where monochloramine is used as a secondary disinfectant, it is important to know its efficacy for a wide range of viruses, as infectious viruses may be introduced in the distribution system where only monochloramine is present. In addition, relatively few studies have investigated the efficacy of monochloramine as systematically as free chlorine; frequently only one concentration, pH, or temperature has been investigated. Two notable exceptions were investigations that examined monochloramine disinfection of human adenovirus 2 (HAdV2) and coxsackievirus B5 (CVB5) at multiple pH levels (21, 31).In 2005, the U.S. Environmental Protection Agency (USEPA) published its second candidate contaminant list (CCL2). The CCL2 is comprised of unregulated microbial and chemical contaminants of potential public health concern that are known or anticipated to occur in drinking water systems and includes: echovirus, coxsackievirus, adenovirus, and calicivirus (36). A number of researchers have reported the disinfection efficacy of free chlorine for representatives of the CCL2 viruses (4, 5, 7, 11, 13, 18, 20, 22, 27, 33, 34, 35), but fewer studies have investigated the disinfection efficacy of monochloramine on these viruses (4, 5, 21, 31). In addition, comparison between existing studies of chlorine or monochloramine disinfection is difficult because of differences in the viruses examined, experimental parameters investigated, and analytical methods used.The present study compared the inactivation kinetics for representative CCL2 viruses with levels of free chlorine and monochloramine recommended for drinking water disinfection. Duplicate experiments with both disinfectants were carried out in pH 7 and 8 buffered chlorine-demand-free (CDF) water at 5°C, with eight viruses chosen to represent the CCL2 virus types. Coxsackieviruses B5 and B3 (CVB5 and CVB3) and echoviruses 1 and 11 (E1 and E11) were chosen based on existing data suggesting resistance to free chlorine, disease implications, and likelihood of presence in higher numbers in natural water. Three representative human adenoviruses were studied, including both serotypes of species F HAdV (40 and 41) that cause gastroenteritis and HAdV2, a representative of respiratory HAdV that may be found in water because they are present in fecal excretions (9). Murine norovirus (MNV), phylogenetically similar to human norovirus and the only norovirus that can be propagated in cell culture, was used as a surrogate for human norovirus. Kinetic inactivation curves are presented, and CT values (disinfectant concentration × time, reported in mg·min/liter) were calculated by using the efficiency factor Hom (EFH) model (16).     

Inactivation of Helicobacter pylori by chlorination.

Three strains of Helicobacter pylori were studied to determine their resistance to chlorination. The organisms were readily inactivated by free chlorine and should therefore be controlled by disinfection practices normally employed in the treatment of drinking water.     

Metal-ion susceptibility of oral bacterial species

Aims: This study aimed to evaluate the effect of lead (Pb) on growth of bacterial species related to dental diseases in vitro. Methods and Results: The effects of lead acetate on representative species of the oral flora were examined at 0·1–10 mmol l^?1 and compared with the effect of silver nitrate and ferrous sulfate. The minimal inhibitory concentration of lead acetate was between 0·15 and 5 mmol l^?1 for the bacterial strains tested. The minimal bactericidal concentration of lead acetate for most oral species was detected in the range of 5–10 mmol l^?1. Silver nitrate at a concentration of 1·25 mmol l^?1 was sufficient to exhibit antibacterial activity against almost all bacteria tested. Ferrous sulfate had the lowest effect. Conclusions: The study indicated a general antimicrobial effect of lead on oral bacterial species in the range of 0·15–10 mmol l^?1. The toxicity of silver nitrate was the highest, whereas that of ferrous sulfate was the lowest. Gram‐positive species had a tendency to be less susceptible for metals than Gram‐negatives. Significance and Impact of the Study: The study shows that it is possible that microbiological changes may occur in the dental plaque in children because of toxic exposure of environmental lead.     

Arthrospira platensis biomass with high protein content cultivated in continuous process using urea as nitrogen source

Aims: Arthrospira platensis has been studied for single‐cell protein production because of its biomass composition and its ability of growing in alternative media. This work evaluated the effects of different dilution rates (D) and urea concentrations (N₀) on A. platensis continuous culture, in terms of growth, kinetic parameters, biomass composition and nitrogen removal. Methods and results: Arthrospira platensis was continuously cultivated in a glass‐made vertical column photobioreactor agitated with Rushton turbines. There were used different dilution rates (0·04–0·44 day^?1) and urea concentrations (0·5 and 5 mmol l^?1). With N₀ = 5 mmol l^?1, the maximum steady‐state biomass concentration was1415 mg l^?1, achieved with D = 0·04 day^?1, but the highest protein content (71·9%) was obtained by applying D = 0·12 day^?1, attaining a protein productivity of 106·41 mg l^?1 day^?1. Nitrogen removal reached 99% on steady‐state conditions. Conclusions: The best results were achieved by applying N₀ = 5 mmol l^?1; however, urea led to inhibitory conditions at D ≥ 0·16 day^?1, inducing the system wash‐out. The agitation afforded satisfactory mixture and did not harm the trichomes structure. Significance and Impact of the Study: These results can enhance the basis for the continuous removal of nitrogenous wastewater pollutants using cyanobacteria, with an easily assembled photobioreactor.