Development of a sporicidal test method for Clostridium difficile

Optimization of Sporulation and Purification Methods for Sporicidal Efficacy Assessment on Bacillus Spores

Validating the efficacy of sporicidal agents is a critical step in current good manufacturing practices for disinfection requirements. A limitation is that the poor quality of spores can lead to false positive sporicidal results. The aim of this study was to explore optimal sporulation and purification methods in Bacillus spores. Spores of seven Bacillus strains were produced in five different sporulation media. After density centrifugation, spore yields were measured by phase-contrast microscopy and enumeration assays. Effects of purification methods including heat, sonication and lysozyme, and maturation on spore qualities were determined by sodium hypochlorite sporicidal assay. Difco Sporulation Media was identified as the preferred sporulation medium for four out of seven tested Bacillus strains. Sporulation rates in B. cereus, B. sphaericus, and B. thuringiensis were higher at 30°C than the rates at 37°C at a difference of 5%, 65%, and 20%, respectively. B. licheniformis favored Mn2+-amended 10% Columbia Broth at 37°C for sporulation with 40-72% higher sporulation rates than other media. The maximum sporulation rates of B. cereus and B. thuringiensis were observed on double-strength Schaeffer's-glucose broth. All studied purification methods improved the spore purity with strain variations. However, intense heat (80°C for 20 min) and lysozyme (100 μg/mL) treatment impaired the spore quality of specific Bacillus strains by sensitizing them against sodium hypochlorite. The length of maturation period had impact on the spore resistance, and the most optimal maturation periods ranged from 7 to 21 days in Bacillus strains. The results of this study will pave the way for further evaluation of sporicidal activity of disinfectants.

Disinfection of surfaces contaminated with Clostridioides difficile endospores using NaCl-derived electrochemically activated solution

BACKGROUND

Clostridioides difficile is transmitted through endospores. Most disinfection procedures for these structures deploy high concentrations of chlorine-derived compounds such as sodium hypochlorite (NaOCl) and sodium dichloroisocyanurate (NaDCC). However, these substances are linked to undesirable public health and environmental issues.

AIM

To compare the efficacy of NaCl-derived electrochemically activated solution (ECAS, 0.18% w/v NaOCl, pH=9.6-10.3), commercial bleach (5000 ppm, 2.83% w/v NaOCl, pH=5.6) and NaDCC (1000 ppm, pH=6.8) to inactivate C. difficile endospores on surfaces using a standard quantitative test (EPA MO-21-03).

FINDINGS

Ten representative reference and field strains from multi-locus sequence typing Clades 1-5 were assayed (N=10). Irrespective of the phylogenetic background of the strains, ECAS showed comparable or better log reduction values [mean=3.22, 95% confidence interval (CI) 0.40-5.56] than bleach (mean=2.74, 95% CI 0.12-5.50) and NaDCC (mean=2.02, 95% CI 0.10-5.12). Cyclic voltammetry measurements revealed similar electrochemical behaviours and open-circuit potentials for ECAS and NaOCl. Congruently, similar morphologies for spores treated with these two compounds were observed by transmission electron microscopy. A factorial design demonstrated that exposure time, but not activation time, influenced the efficacy of ECAS.

CONCLUSIONS

ECAS and NaOC were found to have functional equivalence and may have a common mechanism of action.

Interlaboratory reproducibility of a test method following 4-field test methodology to evaluate the susceptibility of Clostridium difficile spores

BACKGROUND

Sporicidal surface disinfection is recommended to control transmission of Clostridium difficile in healthcare facilities. EN 17126 provides a method to determine the sporicidal activity in suspension and has been approved as a European standard. In addition, a sporicidal surface test has been proposed.

AIM

To determine the interlaboratory reproducibility of a test method for evaluating the susceptibility of a C. difficile spore preparation to a biocidal formulation following the 4-field test (EN 16615 methodology).

METHODS

Nine laboratories participated. C. difficile NCTC 13366 spores were used. Glutaraldehyde (1% and 6%; 15 min) and peracetic acid (PAA; 0.01% and 0.04%; 15 min) were used to determine the spores' susceptibility in suspension in triplicate.

FINDINGS

One-percent glutaraldehyde revealed a mean decimal log₁₀ reduction of 1.03 with variable results in the nine laboratories (0.37-1.49) and a reproducibility of 0.38. The effect of 6% glutaraldehyde was stronger (mean: 2.05; range: 0.96-4.29; reproducibility: 0.86). PAA revealed similar results. An exemplary biocidal formulation based on 5% PAA was used at 0.5% (non-effective concentration) and 4% (effective concentration) to determine the sporicidal efficacy (4-field test) under clean conditions in triplicate with a contact time of 15 min. When used at 0.5% it demonstrated an overall log₁₀ reduction of 2.68 (range: 2.35-3.57) and at 4% of 4.61 (range: 3.82-5.71). The residual contamination on the three primarily uncontaminated test fields was <50 cfu/25 cm² in one out of nine laboratories (0.5%) and in seven out of nine laboratories (4%).

CONCLUSION

The interlaboratory reproducibility seems to be robust.

Disinfectants: The role of standardised testing to aid selection. Part 2

Choosing which disinfectant(s) to use in any particular healthcare environment is a far from trivial task and one that is undertaken by Infection Prevention and Control (IPC) professionals on a regular basis. The recent proliferation in the number and type of products designed to disinfect healthcare surfaces makes for a seemingly bewildering range of options. The primary factor to consider is whether the disinfectant is capable of killing the likely (but unknown) microbial challenge. For reusable non-invasive care equipment, standardised testing provides objective evidence for IPC teams. This second paper seeks to explain these tests and the conditions under which they are performed to aid in the IPC teams’ disinfection selection.

Effectiveness of various cleaning and disinfectant products on Clostridium difficile spores of PCR ribotypes 010, 014 and 027

Background

In healthcare facilities, Clostridium difficile infections spread by transmission of bacterial spores. Appropriate sporicidal disinfectants are needed to prevent development of clusters and outbreaks. In this study different cleaning/disinfecting wipes and sprays were tested for their efficacy against spores of distinctive C. difficile PCR ribotypes.

Methods

Four different products were tested; 1) hydrogen peroxide 1.5%; 2) glucoprotamin 1.5%; 3) a mixture of ethanol, propane and N-alkyl amino propyl glycine; and 4) a mixture of didecyldimonium chloride, benzalkonium chloride, polyaminopropyl, biguanide and dimenthicone as active ingredients. Tiles were contaminated with a test solution containing a concentration of 5x10⁶CFU/ml spores of C. difficile strains belonging to PCR ribotypes 010, 014 or 027. The tiles were left to dry for an hour and then wiped or sprayed with one of the sprays or wipes as intended by the manufacturers. When products neutralized after 5 min, microbiological cultures and ATP measures were performed.

Results

Irrespective of the disinfection method, the microbial count log₁₀ reduction of C. difficile PCR ribotype 010 was highest, followed by the reduction of C. difficile 014 and C. difficile 027. Overall, the wipes performed better than the sprays with the same active ingredient. On average, although not significantly, a difference in relative light units (RLU) reduction between the wipes and sprays was found. The wipes had a higher RLU log₁₀ reduction, but no significant difference for RLU reduction was observed between the different C. difficile strains (p = 0.16).

Conclusion

C. difficile spores of PCR ribotypes 014 and 027 strains are more difficult to eradicate than non-toxigenic PCR ribotype 010. In general, impregnated cleaning/disinfection wipes performed better than ready-to-use sprays. Wipes with hydrogen peroxide (1.5%) showed the highest bactericidal activity.