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.     

Chlorine dioxide disinfection of single and dual species biofilms,detached biofilm and planktonic cells

Disinfection efficacy testing is usually done with planktonic cells or more recently, biofilms. While disinfectants are much less effective against biofilms compared to planktonic cells, questions regarding the disinfection tolerance of detached biofilm clusters remain largely unanswered. Burkholderia cepacia and Pseudomonas aeruginosa were grown in chemostats and biofilm tubing reactors, with the tubing reactor serving as a source of detached biofilm clusters. Chlorine dioxide susceptibility was assessed for B. cepacia and P. aeruginosa in these three sample types as monocultures and binary cultures. Similar doses of chlorine dioxide inactivated samples of chemostat and tubing reactor effluent and no statistically significant difference between the log₁₀ reductions was found. This contrasts with chlorine, shown previously to be generally less effective against detached biofilm particles. Biofilms were more tolerant and required chlorine dioxide doses ten times higher than chemostat and tubing reactor effluent samples. A second species was advantageous in all sample types and resulted in lower log₁₀ reductions when compared to the single species cultures, suggesting a beneficial interaction of the species.     

Chlorine dioxide disinfection of single and dual species biofilms, detached biofilm and planktonic cells

Disinfection efficacy testing is usually done with planktonic cells or more recently, biofilms. While disinfectants are much less effective against biofilms compared to planktonic cells, questions regarding the disinfection tolerance of detached biofilm clusters remain largely unanswered. Burkholderia cepacia and Pseudomonas aeruginosa were grown in chemostats and biofilm tubing reactors, with the tubing reactor serving as a source of detached biofilm clusters. Chlorine dioxide susceptibility was assessed for B. cepacia and P. aeruginosa in these three sample types as monocultures and binary cultures. Similar doses of chlorine dioxide inactivated samples of chemostat and tubing reactor effluent and no statistically significant difference between the log(10) reductions was found. This contrasts with chlorine, shown previously to be generally less effective against detached biofilm particles. Biofilms were more tolerant and required chlorine dioxide doses ten times higher than chemostat and tubing reactor effluent samples. A second species was advantageous in all sample types and resulted in lower log(10) reductions when compared to the single species cultures, suggesting a beneficial interaction of the species.     

Chlorine disinfection facilitates natural transformation through ROS-mediated oxidative stress

The bacterial infection that involves antimicrobial resistance is a rising global threat to public health. Chlorine-based water disinfection processes can inactivate antibiotic resistant bacteria. However, at the same time, these processes may cause the release of antibiotic resistance genes into the water as free DNA, and consequently increase the risk to disseminate antibiotic resistance via natural transformation. Presently, little is known about the contribution of residual chlorine affecting the transformation of extracellular antibiotic resistance genes (ARGs). This study investigates whether chloramine and free chlorine promote the transformation of ARGs and how this may occur. We reveal that both chloramine and free chlorine, at practically relevant concentrations, significantly stimulated the transformation of plasmid-encoded ARGs by the recipient Acinetobacter baylyi ADP1, by up to a 10-fold increase. The underlying mechanisms underpinning the increased transformations were revealed. Disinfectant exposure induced a series of cell responses, including increased levels of reactive oxygen species (ROS), bacterial membrane damage, ROS-mediated DNA damage, and increased stress response. These effects thus culminated in the enhanced transformation of ARGs. This promoted transformation was observed when exposing disinfectant-pretreated A. baylyi to free plasmid. In contrast, after pretreating free plasmid with disinfectants, the transformation of ARGs decreased due to the damage of plasmid integrity. These findings provide important insight on the roles of disinfectants affecting the horizontal transfer of ARGs, which could be crucial in the management of antibiotic resistance in our water systems.Subject terms: Antibiotics, Public health     

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.     

Chlorine disinfection of atypical mycobacteria isolated from a water distribution system

We studied the resistance of various mycobacteria isolated from a water distribution system to chlorine. Chlorine disinfection efficiency is expressed as the coefficient of lethality (liters per minute per milligram) as follows: Mycobacterium fortuitum (0.02) > M. chelonae (0.03) > M. gordonae (0.09) > M. aurum (0.19). For a C.t value (product of the disinfectant concentration and contact time) of 60 mg.min.liter(-1), frequently used in water treatment lines, chlorine disinfection inactivates over 4 log units of M. gordonae and 1.5 log units of M. fortuitum or M. chelonae. C.t values determined under similar conditions show that even the most susceptible species, M. aurum and M. gordonae, are 100 and 330 times more resistant to chlorine than Escherichia coli. We also investigated the effects of different parameters (medium, pH, and temperature) on chlorine disinfection in a chlorine-resistant M. gordonae model. Our experimental results follow the Arrhenius equation, allowing the inactivation rate to be predicted at different temperatures. Our results show that M. gordonae is more resistant to chlorine in low-nutrient media, such as those encountered in water, and that an increase in temperature (from 4 degrees C to 25 degrees C) and a decrease in pH result in better inactivation.     

Chlorine dioxide sterilization of implanted right atrial catheters in rabbits

The disinfection of right atrial catheters in situ using chlorine dioxide was investigated. Catheters were implanted into rabbits (Oryctolagus cuniculi) and colonized by inoculation of Staphylococcus aureus, Sa-80, into the lumen. All of the catheters were colonized and the difference in numbers of bacteria recovered from animals destined for the control and disinfection groups was not significant. Animals were assigned randomly to the control or disinfection group. Treatment consisted of filling the catheter lumen of the disinfection group with chlorine dioxide and of the control group with sterile physiological saline daily for 15 minutes. In addition, both groups received systemic antimicrobial therapy. Cultures of blood withdrawn from the catheters and by venipuncture were negative for five of the nine control group animals after treatment for 5 days. Four control group catheters failed, after from 3 to 21 treatments, without ever achieving negative cultures. All nine animals in the disinfection group had negative cultures after treatment for 5 days. Subsequently, one animal from each group reverted to positive cultures. All nine control group catheters failed during the study, compared to only three disinfection group catheters (p less than 0.01). At necropsy, culture of cardiac blood, thrombi and catheter tubing sections demonstrated colonization of six in the control group and only one in the disinfection group (p less than 0.05). Rabbits tolerated the chlorine dioxide disinfection well and no adverse signs were noted.     

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 degrees 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 log(10) and 2.0 log(10) 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 log(10) 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.     

Carbon dioxide and temperature effects on forage establishment: tissue composition and nutritive value

Atmospheric CO₂ concentration ([CO₂]) and temperature are likely to increase in the future and may change plant growth and composition characteristics. Rhizoma peanut (Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flügge) were grown on a natural field soil in temperature-gradient greenhouses to evaluate the effects of elevated [CO₂] and temperature on tissue composition and digestibility during the establishment year. Carbon dioxide levels were maintained at 365 (ambient) and 640 μL CO₂ L^–1 air. The temperature-gradient greenhouses were regulated to obtain air temperature sectors of 0.2, 1.5, 2.9, and 4.5 °C above ambient. Samples were taken of previously undefoliated herbage at 57, 86, 121, 148, and 217 days after planting and entire plots were harvested at 218 days after planting. Elevated [CO₂] increased total nonstructural carbohydrate concentration in rhizoma peanut leaves by almost 50%. Rhizoma peanut leaf N concentration was 6% lower at elevated than at ambient [CO₂]. The N concentration in new rhizomes of rhizoma peanut was increased by high [CO₂], while the N concentration in bahiagrass was not affected by temperature or [CO₂]. No effects of [CO₂] and temperature were found on neutral detergent fibre in rhizoma peanut leaves or stems; however, elevated [CO₂] increased neutral detergent fibre in bahiagrass leaves. Only at season end was in vitro organic matter digestion of rhizoma peanut higher at ambient (623 g kg^–1) than at elevated [CO₂] (609 g kg^–1). Elevated [CO₂] had a greater effect on tissue composition of rhizoma peanut than of bahiagrass. These data suggest that elevated temperature and CO₂-induced changes in chemical composition of forage species adapted to humid subtropics will be relatively small, particularly for C4 species.     

Interactive effects of elevated carbon dioxide and growth temperature on photosynthesis in cotton leaves

Cotton (Gossypium hirsutum L., cv DPL 5415) plants were grown in naturally lit environment chambers at day/night temperature regimes of 26/18 (T-26/18), 31/23 (T-31/23) and 36/28 °C (T-36/28) and CO2 concentrations of 350 (C-350), 450 (C-450) and 700 L L-1 (C-700). Net photosynthesis rates, stomatal conductance, transpiration, RuBP carboxylase activity and the foliar contents of starch and sucrose were measured during different growth stages. Net CO2 assimilation rates increased with increasing CO2 and temperature regimes. The enhancement of photosynthesis was from 24 mol CO2 m-2 s-1 (with C-350 and T-26/18) to 41 mol m-2 s-1 (with C-700 and T-36/28). Stomatal conductance decreased with increasing CO2 while it increased up to T-31/23 and then declined. The interactive effects of CO2 and temperature resulted in a 30% decrease in transpiration. Although the leaves grown in elevated CO2 had high starch and sucrose concentrations, their content decreased with increasing temperature. Increasing temperature from T-26/18 to 36/28 increased RuBP carboxylase activity in the order of 121, 172 and 190 mol mg-1 chl h-1 at C-350, C-450 and C-700 respectively. Our data suggest that leaf photosynthesis in cotton benefited more from CO_2 enrichment at warm temperatures than at low growth temperature regimes.     

Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity

The photocatalytic properties of titanium dioxide are well known and have many applications including the removal of organic contaminants and production of self-cleaning glass. There is an increasing interest in the application of the photocatalytic properties of TiO₂ for disinfection of surfaces, air and water. Reviews of the applications of photocatalysis in disinfection (Gamage and Zhang 2010; Chong et al., Wat Res 44(10):2997–3027, 2010) and of modelling of TiO₂ action have recently been published (Dalrymple et al. , Appl Catal B 98(1–2):27–38, 2010). In this review, we give an overview of the effects of photoactivated TiO₂ on microorganisms. The activity has been shown to be capable of killing a wide range of Gram-negative and Gram-positive bacteria, filamentous and unicellular fungi, algae, protozoa, mammalian viruses and bacteriophage. Resting stages, particularly bacterial endospores, fungal spores and protozoan cysts, are generally more resistant than the vegetative forms, possibly due to the increased cell wall thickness. The killing mechanism involves degradation of the cell wall and cytoplasmic membrane due to the production of reactive oxygen species such as hydroxyl radicals and hydrogen peroxide. This initially leads to leakage of cellular contents then cell lysis and may be followed by complete mineralisation of the organism. Killing is most efficient when there is close contact between the organisms and the TiO₂ catalyst. The killing activity is enhanced by the presence of other antimicrobial agents such as Cu and Ag.     

Measurement of chlorine dioxide penetration in dairy process pipe biofilms during disinfection

Biofilms are considered a significant health risk in the food and dairy industries because they can harbor pathogens, and direct contact with them can lead to food contamination. Biofilm control is often performed using strong oxidizing agents like chlorine and peracetic acid. Although chlorine dioxide (ClO₂) is being used increasingly to control microbiological growth in a number of different industries, not much is known about disinfection in biofilms using chlorine dioxide. In this study, a microelectrode originally made for chlorine detection was modified to measure the profiles of chlorine dioxide in biofilm as a function of depth into the biofilm. In addition, discarded microelectrodes proved useful for in situ direct measurement of biofilm thicknesses. The chlorine dioxide microelectrode had a linear response when calibrated up to a ClO₂ concentration of 0.4 mM. ClO₂ profiles showed depletion of disinfectant at 100 μm in the biofilm depth, indicating that ClO₂ may not reach bacteria in a biofilm thicker than this using a 25 mg/l solution.     

Facility for studying the effects of elevated carbon dioxide concentration and increased temperature on crops

The requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi-controlled plant growth facility is described which allows the study of elevated CO₂ and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO₂ concentrations of 363 and 692 cm³ m^?3 for targets of 350 and 700 cm³ m^?3 respectively. Temperatures were set to follow outside ambient or outside ambient +4°C, and hourly means were within 0.5°C of the target for 92% of the time for target temperatures greater than 6°C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifieal light with natural photoperiod) was 2% greater than the total measured outside over the same period.     

Chlorine, chloramine, chlorine dioxide, and ozone susceptibility of Mycobacterium avium

Environmental and patient isolates of Mycobacterium avium were resistant to chlorine, monochloramine, chlorine dioxide, and ozone. For chlorine, the product of the disinfectant concentration (in parts per million) and the time (in minutes) to 99.9% inactivation for five M. avium strains ranged from 51 to 204. Chlorine susceptibility of cells was the same in washed cultures containing aggregates and in reduced aggregate fractions lacking aggregates. Cells of the more slowly growing strains were more resistant to chlorine than were cells of the more rapidly growing strains. Water-grown cells were 10-fold more resistant than medium-grown cells. Disinfectant resistance may be one factor promoting the persistence of M. avium in drinking water.     

Determining the disinfection of textiles in compressed carbon dioxide using various indicator microbes

Aims: This paper presents a research on the disinfection efficiency of inoculated textile swatches by compressed carbon dioxide, an environmental friendly way to disinfect textiles as opposed to the conventional laundering procedures using water. The disinfection efficiency was determined by using the following microbes inoculated on cotton test fabrics: Enterococcus faecium, Enterobacter aerogenes and Candida albicans. Methods and Results: The experiments were performed using the high pressure extraction device with a maximum pressure of 50 MPa and a small extraction vessel of 500 ml. Pure CO₂ and CO₂ with added disinfection agent or commercial detergent were used. The chosen disinfecting agent was hydrogen peroxide, a widespread disinfecting chemical. It was found that treatment with CO₂ for 25 min at 5 MPa and 40°C (313K) and the addition of 4 ml of specific detergent per litre of CO₂ assures at least a five log step reduction of Enterobacter aerogenes and C. albicans, whilst treatment at 50°C (323K) with CO₂ for 25 min at 5 MPa is sufficient for at least a five log step reduction for Enterococcus faecium. It was also found that a 15‐min CO₂ treatment at 7 MPa and 20°C (293K) was sufficient for the inactivation of the yeast C. albicans, whilst these conditions were not rigorous enough for the challenge bacteria. On the other hand, the labscale treatment with CO₂ for 25 min at pressure 4 and 6 MPa with the addition of detergent or hydrogen peroxide only yields a log step reduction of up to 4 log steps, thus proving the slightly disinfective properties of the CO₂ treatment with added agents, but not reaching efficient results as a 5 log step reduction was not reached. Conclusions: Addition of heat to the compressed CO₂ treatment of textiles inoculated with microorganisms proved more effective than the addition of detergent or disinfectant with compressed CO₂ treatment at temperature of 20°C. Significance and Impact of the Study: CO₂ treatment of textiles is a promising ecological alternative dry‐cleaning method for the disinfection of medical textiles.     

Kinetics of ultrasonic disinfection of Escherichia coli in the presence of titanium dioxide particles

The ultrasonic disinfection of Escherichia coli was carried out in the presence of anatase-type TiO2 particles, and the effectiveness of the combination of ultrasonic irradiation with TiO2 addition was verified. The rate constant was determined from the plot of the common logarithm of the survival cell ratio versus the ultrasonic irradiation time using first-order kinetics. In the absence of particles, the rate constant was proportional to the ultrasonic power. When ultrasonic disinfection was carried out in the presence of TiO2 particles, which have a radical generation ability, the rate of disinfection was remarkably faster than that in the absence of TiO2. In the presence of silica particles, which have no radical generation ability, the rate of disinfection was the same as that in the absence of TiO2. These results suggest that the radical generation ability of TiO2 appeared as a result of the ultrasonic irradiation. The effect of the amount of TiO2 on the rate of disinfection was also examined. The rate constant for disinfection in the presence of TiO2 was saturated to a certain value and was represented using the Langmuir-type equation. The proposed model well describes the effects of the ultrasonic power and the amount of TiO2 on the rate constant for disinfection.     

The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source-sink relations and respiration

Abstract. Herbaceous C₃ plants grown in elevated CO₂ show increases in carbon assimilation and carbohydrate accumulation (particularly starch) within source leaves. Although changes in the partitioning of biomass between root and shoot occur, the proportion of this extra assimilate made available for sink growth is not known. Root:shoot ratios tend to increase for CO₂-enriched herbaceous plants and decrease for CO₂-enriched trees. Root:shoot ratios for cereals tend to remain constant. In contrast, elevated temperatures decrease carbohydrate accumulation within source and sink regions of a plant and decrease root:shoot ratios. Allometric analysis of at least two species showing changes in root: shoot ratios due to elevated CO₂ show no alteration in the whole-plant partitioning of biomass. Little information is available for interactions between temperature and CO₂. Cold-adapted plants show little response to elevated levels of CO₂, with some species showing a decline in biomass accumulation. In general though, increasing temperature will increase sucrose synthesis, transport and utilization for CO₂-enriched plants and decrease carbohydrate accumulation within the leaf. Literature reports are discussed in relation to the hypothesis that sucrose is a major factor in the control of plant carbon partitioning. A model is presented in support.