Comparison of commercial disinfectants and an in loco-produced solution: free residual chlorine decay in human supply waters

Disinfection process is used in the treatment of water for human supply to promote sanitary safety and provide users with drinking water that meets potability standards. Thus, it is necessary to sustain a minimal concentration of free residual chlorine (FRC) throughout the entire distribution system. The present study investigated the decay process of FRC concentration in water destined for human supply. The decay was evaluated in bench-scale testing, using sodium hypochlorite, calcium hypochlorite, sodium dichloroisocyanurate (organic chlorine) as disinfectant agents, and also an alternative disinfectant solution (ADS) produced in loco, with oxidizing and disinfectant properties, which is being used in Brazilian sanitation industry. To evaluate the decay, four models were fitted: first-order, nth-order, limited first-order and parallel first-order, hence determining the corresponding parameters which describe the decay speed of the FRC concentration in water. Achieved results demonstrated that all models were statistically significant and predictive. However, parallel first-order model produced the best fit. Regarding the evaluated disinfectants, it was noted the preeminence of ADS solution when compared to the others, since it imparted a higher FRC over time, a behavior indicated by lower values for reaction rate constant in all models and when compared to other disinfectants used in this study.

The effect of Combined Treatment with Sodium Dichloroisocyanurate and Electron Beam Irradiation in Controlling Mold (Lasiodiplodia theobromae) on Star Apples

Lasiodiplodia theobromae causes decay of star apple fruits (Chrysophyllum cainino) during harvest, transport and storage. If the irradiation dose is higher than 800 Gy, this mold will be controlled. However, the quality of star apple was significantly changed when they were irradiated at the dose higher than 0.6 kGy by electron beam (EB). To keep irradiation dose under 0.6kGy, the synergic effect of the combined treatment of EB irradiation and sodium dichloroisocyanurate (NaDCC) was investigated. In this study, star apples were pretreated with NaDCC concentrations in range of 10 -70 ppm in order to decrease the growth of mold and extend the shelf-life of treated star apples. The results showed that pretreatment with 20 ppm NaDCC had also kept the color and reduced disease of stored star apple. Dipping star apples into 20 ppm NaDCC solution before irradiating at 400 Gy and 600 Gy could be chosen as the best way to inhibit the development of Lasiodiplodia theobromae and extend the shelf life of star apple in the trading condition (7 days, 9oC).

Humidifier disinfectant, sodium dichloroisocyanurate (NaDCC): assessment of respiratory effects to protect workers’ health

In South Korea, it has been found that biocides used to control and eliminate harmful organisms are used as humidifier disinfectants and cause lung disease in users. Hence, efforts have been focused on studying the toxicity of biocides in workers who handle them. The purpose of this study was to evaluate the effects of inhalation exposure to sodium dichloroisocyanurate (NaDCC) to protect the health of workers handling NaDCC. F344 rats were exposed to 0.8-, 4-, and 20-mg/m3 of NaDCC for 6 h per day, 5 days per week for 14 days, and the recovery period after exposure was 14 days. In the 20-mg/m3-exposure group, we observed a decrease in food intake in females, a weight loss in males, and a decrease in partially active thromboplastin time in males and females 2 weeks after exposure. We noted a decrease in white blood cells in males in the 4- and 20-mg/m3-exposed groups. Both males and females in the 20-mg/m3 group and males in the 4-mg/m3 group showed irritation in the larynx related to test substance exposure. However, these findings were not observed in the recovery group. The main target organs affected by repeated 2-week inhalation exposure to NaDCC were the nasal cavity and larynx in the upper respiratory tract. The No Observed Adverse Effect Level (NOAEL) was considered to be 0.8 mg/m3 because effects related to NaDCC exposure were observed even at of 4 mg/m3, and these effects were found to be reversible.

Resistance of Clostridioides difficile spores (Clostridiales: Peptostreptococcaceae) to sodium dichloroisocyanurate

Clostridioides difficile is a significant cause of diarrhea in hospitals and the community. This bacterial pathogen is transmitted through the ingestion of endospores, which are challenging to eliminate due to intrinsic resistance to a variety of chemical disinfection agents. The well-characterized laboratory strain CD630 displays low virulence, has not caused outbreaks, and is highly susceptible to disinfectants. Nonetheless, a closely related strain termed NAPCR1 caused outbreaks in Costa Rica and later became endemic in many hospitals from this country. This strain causes disease through unusual mechanisms and is genotypically distinct from CD630. Consequently, its epidemic potential could be influenced by as yet unknown spore phenotypes, such as increased resistance to disinfectants. Objective: To determine whether the NAPCR1 strain is more resistant to a conventional and highly effective C. difficile sporicidal agent than strain CD630 and to identify potential explanatory mechanisms at the genomic level. Methods: We used an in vitro dilution-neutralization method to calculate the sporicidal activity of sodium dichloroisocyanurate (DCC) against purified spores from three subtypes of NAPCR1 isolates (LIBA-2945, LIBA-5761, and LIBA-6276), CD630, and a representative of the highly virulent and epidemic NAP1 strain (LIBA-5758). This phenotypic characterization was complemented with a genomics-steered search of polymorphisms in 15 spore- or sporulation-related genes. Results: Whereas DCC at a final concentration of 0.1 % (w/v) eradicated CD630 endospores with high efficacy (log10 reduction factor (LFR) ≥ 5), it only partially inactivated NAPCR1 (average LFR range: = 1.77-3.37) and NAP1 endospores (average LRF = 3.58). As hypothesized, the three NAPCR1 subtypes tested were more resistant to DCC than strain CD630 (ANOVA, P < 0.05), with LIBA-5761 showing the highest level of DCC resistance overall (ANOVA, P < 0.05). All three NAPCR1 isolates showed large deletions in bclA1. Besides, isolates LIBA-5761 and LIBA-6276 had deletions in bclA2. Conclusions: Our in vitro tests revealed a differential resistance of spores from the C. difficile NAPCR1 strain to DCC. They highlight the importance of continuously evaluating the efficacy of deployed disinfection agents against circulating strains and hint to a potential role of structural proteins from the exosporium in resistance to disinfectants in C. difficile.

Humidifier disinfectant, sodium dichloroisocyanurate (NaDCC): Assessment of respiratory effects to protect workers’ health

Biocides are used to control and remove all harmful organisms. In South Korea, they are used in humidifier disinfectants and have been found to cause lung disease in users. Hence, efforts have been focused on studying the toxicity of biocides in workers who handle them. The purpose of this study was to evaluate the effects of inhalation exposure to sodium dichloroisocyanurate (NaDCC) to protect the health of workers handling NaDCC. F344 rats were exposed to 0.8-, 4-, and 20-mg/m3 of NaDCC for 6 hours per day, 5 days per week for 14 days, and the recovery period after exposure was 14 days.In the 20-mg/m3 exposure group, we observed a decrease in food intake in females, a weight loss in males, and a decrease in partially active thromboplastin time in males and females 2 weeks after exposure. We noted a decrease in white blood cells in males in the 4- and 20-mg/m3 exposed groups. Both males and females in the 20-mg/m3 group and males in the 4-mg/m3 group showed irritation in the larynx related to test substance exposure. However, these findings were not observed in the recovery group. The main target organs affected by repeated 2-week inhalation exposure to NaDCC were the nasal cavity and larynx in the upper respiratory tract. The No Observed Adverse Effect Level (NOAEL) was considered to be 0.8 mg/m3 because the effects related to exposure of NaDCC were observed even at of 4 mg/m3. In addition, these effects were found to be reversible.

Managing the Bacterial Contamination Risk in an Axenic Mice Animal Facility

A gap exists between good laboratory practises with axenic animals and procedures applied. This work aimed at choosing the appropriate disinfectant between sodium dichloroisocyanurate (MB-10) and potassium peroxymonosulfate (Virkon^™) disinfectants and to adjust the soaking time of the material used with ISOcage biosafety stations. Another aim was to compare the microbial load on cage systems hosting mice since two weeks in axenic (AR) rooms and typical specific-pathogen-free (SPF) non-axenic rooms (NAR) to identify resistant microorganisms targeted for longer soaking disinfection as well as evaluate microbial concentration reduction procedures in AR. <i>Staphylococcus</i> was the most frequently isolated genus (AR and NAR). An average of three spore-forming microorganisms per cage were counted from AR. The disinfection time to reach 1 log reduction for <i>Bacillus atrophaeus</i> spores varied from 138 (100 ppm MB-10) to 290 (Virkon^™) seconds and below 20 seconds for <i>S. epidermidis</i> (100 ppm MB-10). AR management protocols lead to 1000 times lower microorganisms burden compared to NAR. Data comparing microbial load on SPF and axenic facilities can be used as comparison for facilities aiming at improving the effectiveness of their microbial control procedures.

Is a reduction in viability enough to determine biofilm susceptibility to a biocide?

Objective: The abundance and prevalence of dry-surface biofilms (DSBs) in hospitals constitute an emerging problem, yet studies rarely report the cleaning and disinfection efficacy against DSBs. Here, the combined impact of treatments on viability, transferability, and recovery of bacteria from DSBs has been investigated for the first time. Methods: Staphylococcus aureus DSBs were produced in alternating 48-hour wet–dry cycles for 12 days on AISI 430 stainless steel discs. The efficacy of 11 commercially available disinfectants, 4 detergents, and 2 contactless interventions were tested using a modified standardized product test. Reduction in viability, direct transferability, cross transmission (via glove intermediate), and DSB recovery after treatment were measured. Results: Of 11 disinfectants, 9 were effective in killing and removing bacteria from S. aureus DSBs with >4 log10 reduction. Only 2 disinfectants, sodium dichloroisocyanurate 1,000 ppm and peracetic acid 3,500 ppm, were able to lower both direct and cross transmission of bacteria (<2 compression contacts positive for bacterial growth). Of 11 disinfectants, 8 could not prevent DSB recovery for >2 days. Treatments not involving mechanical action (vaporized hydrogen peroxide and cold atmospheric plasma) were ineffective, producing <1 log10 reduction in viability, DSB regrowth within 1 day, and 100% transferability of DSB after treatment. Conclusions: Reduction in bacterial viability alone does not determine product performance against biofilm and might give a false sense of security to consumers, manufacturers and regulators. The ability to prevent bacterial transfer and biofilm recovery after treatment requires a better understanding of the effectiveness of biocidal products.