Efficacy of novel aqueous photo-chlorine dioxide against a human norovirus surrogate, bacteriophage MS2 and Clostridium difficile endospores, in suspension, on stainless steel and under greenhouse conditions

Efficacy of photoClO2 against two human norovirus surrogates and Clostridioides difficile endospores on stainless steel and nylon carpet

AIMS

Determine efficacy of an aqueous photocatalytic disinfection system, photoClO2, against two human norovirus surrogates [feline calicivirus (FCV) and Tulane virus (TuV)] and Clostridioides difficile endospores on stainless steel and nylon carpet.

METHODS AND RESULTS

The photoClO2 system was first optimized with 1% sodium chlorite (NaClO2) and 10 ppm Eosin Y to produce 60.64 ppm ClO2/min in a 4.5 × 4.5 cm2 area. It was then tested against FCV, TuV, and C. difficile endospores on stainless steel and nylon carpet with two different backings. On stainless steel, photoClO2 achieved a > 5 log10 plaque-forming unit (PFU) reduction of FCV in 45 min, >3 log10 median tissue culture infectious dose (TCID50) reduction of TuV in 60 min, and 1.3 log10 colony-forming unit (CFU) reduction of C. difficile endospores in 120 min. Under indoor lighting conditions, photoClO2 achieved a 4.3 log10 PFU reduction of FCV and 1.4 log10 TCID50 reduction of TuV on stainless steel after 120 min. Further, photoClO2 achieved a 2.9 log10 PFU reduction of FCV and 2.5 log10 TCID50 reduction of TuV on nylon carpet with waterproof backing in 60 min, which was higher than carpet with water-permeable backing (1.3 log10 PFU and 1.1 log10 TCID50 reduction, respectively).

CONCLUSION

ClO2 production rate of the photoClO2 system was influenced by light distribution, while disinfection efficacy was affected by light intensity, surface characteristics, and target microorganisms. PhotoClO2 was efficacious in inactivating both human norovirus surrogates on stainless steel and nylon carpet. Efficacy against C. difficile endospores was limited.

Assessing viral freshwater hazard using a toxicokinetic model and Dreissena polymorpha

The detection all pathogenic enteric viruses in water is expensive, time-consuming, and limited by numerous technical difficulties. Consequently, using reliable indicators such as F-specific RNA phages (FRNAPH) can be well adapted to assess the risk of viral contamination of fecal origin in surface waters. However, the variability of results inherent to the water matrix makes it difficult to use them routinely and to interpret viral risk. Spatial and temporal variability of surface waters can lead to underestimate this risk, in particular in the case of low loading. The use of bivalve mollusks as accumulating systems appears as a promising alternative, as recently highlighted with the freshwater mussel Dreissena polymorpha, but its capacity to accumulate and depurate FRNAPH needs to be better understood and described. The purpose of this study is to characterise the kinetics of accumulation and elimination of infectious FRNAPH by D. polymorpha in laboratory conditions, formalised by a toxico-kinetic (TK) mechanistic model. Accumulation and depuration experiments were performed at a laboratory scale to determine the relationship between the concentration of infectious FRNAPH in water and the concentration accumulated by D. polymorpha. The mussels accumulated infectious FRNAPH (3-5.4 × 104 PFU/g) in a fast and concentration-dependent way in only 48 h, as already recently demonstrated. The second exposure demonstrated that the kinetics of infectious FRNAPH depuration by D. polymorpha was independent to the exposure dose, with a T90 (time required to depurate 90 % of the accumulated concentration) of approximately 6 days. These results highlight the capacities of D. polymorpha to detect and reflect the viral pollution in an integrative way and over time, which is not possible with point water sampling. Different TK models were fitted based on the concentrations measured in the digestive tissues (DT) of D. polymorpha. The model has been developed to formalise the kinetics of phage accumulation in mussels tissues through the simultaneous estimation of accumulation and depuration rates. This model showed that accumulation depended on the exposure concentration, while depuration did not. Standardized D. polymorpha could be easily transplanted to the environment to predict viral concentrations using the TK model defined in the present study to predict the level of contamination of bodies of water on the basis of the level of phages accumulated by the organisms. It will be also provide a better understanding of the dynamics of the virus in continental waters at different time and spatial scales, and thereby contribute to the protection of freshwater resources.

Surrogate Selection for Foot-and-Mouth Disease Virus in Disinfectant Efficacy Tests by Simultaneous Comparison of Bacteriophage MS2 and Bovine Enterovirus Type 1

In South Korea, testing disinfectants against foot-and-mouth disease virus (FMDV) that are contagious in livestock or that require special attention with respect to public hygiene can be manipulated only in high-level containment laboratories, which are not easily available. This causes difficulties in the approval procedure for disinfectants, such as a prolonged testing period. Additionally, the required biosafety level (BSL) in the case of FMDV has hindered its extensive studies. However, this drawback can be circumvented by using a surrogate virus to improve the performance of the efficacy testing procedure for disinfectants. Therefore, we studied bacteriophage MS2 (MS2) and bovine enterovirus type 1 (ECBO) with respect to disinfectant susceptibility for selecting a surrogate for FMDV according to the Animal and Plant Quarantine Agency (APQA) guidelines for efficacy testing of veterinary disinfectants. Effective concentrations of the active substances in disinfectants (potassium peroxymonosulfate, sodium dichloroisocyanurate, malic acid, citric acid, glutaraldehyde, and benzalkonium chloride) against FMDV, MS2, and ECBO were compared and, efficacies of eight APQA-listed commercial disinfectants used against FMDV were examined. The infectivity of FMDV and ECBO were confirmed by examination of cytopathic effects, and MS2 by plaque assay. The results reveal that the disinfectants are effective against MS2 and ECBO at higher concentrations than in FMDV, confirming their applicability as potential surrogates for FMDV in efficacy testing of veterinary disinfectants.

Imaging and plate counting to quantify the effect of an antimicrobial: A case study of a photo-activated chlorine dioxide treatment

AIM

Assess removal versus kill efficacies of antimicrobial treatments against thick biofilms with statistical confidence.

METHODS AND RESULTS

A photo activated chlorine dioxide treatment (Photo ClO₂ ) was tested in two independent experiments against thick (>100 μm) Pseuodmonas aeruginosa biofilms. Kill efficacy was assessed by viable plate counts. Removal efficacy was assessed by 3D confocal scanning laser microscope imaging (CSLM). Biovolumes were calculated using an image analysis approach that models the penetration limitation of the laser into thick biofilms using Beer's Law. Error bars are provided that account for the spatial correlation of the biofilm's surface. The responsiveness of the biovolumes and plate counts to the increasing contact time of Photo ClO₂ were quite different, with a massive 7 log reduction in viable cells (95% CI: 6.2, 7.9]) but a more moderate 73% reduction in biovolume (95% CI: [60%, 100%]). Results are leveraged to quantitatively assess candidate CSLM experimental designs of thick biofilms .

CONCLUSIONS

Photo ClO₂ kills but only partially removes the biofilm from the surface. To maximize statistical confidence in assessing removal, imaging experiments should use fewer pixels in each z-slice, and more importantly, at least 2 independent experiments even if there is only a single field of view in each experiment.

SIGNIFICANCE AND IMPACT OF STUDY

There is limited penetration depth when collecting 3D confocal images of thick biofilms. Removal can be assessed by optimally fitting Beer's Law to all of the intensities in a 3D image and by accounting for the spatial correlation of the biofilm's surface. For thick biofilms, other image analysis approaches are biased or do not provide error bars. We generate unbiased estimates of removal and assess candidate CSLM experimental designs of thick biofilms with different pixilations, numbers of fields of view and numbers of experiments using the included design tool.