Innate resistance to sporicides and potential failure to decontaminate

Review of techniques for the in-situ sterilization of soil contaminated with Bacillus anthracis spores or other pathogens

This review summarizes the literature on efficacy of techniques to sterilize soil. Soil may need to be sterilized if contaminated with pathogens such as Bacillus anthracis. Sterilizing soil in-situ minimizes spread of the bio-contaminant. Soil is difficult to sterilize, with efficacy generally diminishing with depth. Methyl bromide, formaldehyde, and glutaraldehyde are the only soil treatment options that have been demonstrated at full-scale to effectively inactivate Bacillus spores. Soil sterilization modalities with high efficacy at bench-scale include wet and dry heat, metam sodium, chlorine dioxide gas, and activated sodium persulfate. Simple oxidants such as chlorine bleach are ineffective in sterilizing soil.

Disinfectants and antiseptics: mechanisms of action and resistance

Chemical biocides are used for the prevention and control of infection in health care, targeted home hygiene or controlling microbial contamination for various industrial processes including but not limited to food, water and petroleum. However, their use has substantially increased since the implementation of programmes to control outbreaks of methicillin-resistant Staphylococcus aureus, Clostridioides difficile and severe acute respiratory syndrome coronavirus 2. Biocides interact with multiple targets on the bacterial cells. The number of targets affected and the severity of damage will result in an irreversible bactericidal effect or a reversible bacteriostatic one. Most biocides primarily target the cytoplasmic membrane and enzymes, although the specific bactericidal mechanisms vary among different biocide chemistries. Inappropriate usage or low concentrations of a biocide may act as a stressor while not killing bacterial pathogens, potentially leading to antimicrobial resistance. Biocides can also promote the transfer of antimicrobial resistance genes. In this Review, we explore our current understanding of the mechanisms of action of biocides, the bacterial resistance mechanisms encompassing both intrinsic and acquired resistance and the influence of bacterial biofilms on resistance. We also consider the impact of bacteria that survive biocide exposure in environmental and clinical contexts.

An Evaluation of Sporicidal Treatments against Blown Pack Spoilage Associated Clostridium estertheticum and Clostridium gasigenes Spores

Blown pack spoilage (BPS) occurs when meat is cross-contaminated with Clostridium estertheticum or Clostridium gasigenes spores, often from the meat processing environment. This study tested the efficacy of four sporicidal disinfectants commonly used in beef processing plants against C. estertheticum and C. gasigenes spores in a suspension test. D-values were obtained under model ‘clean’ (sterile distilled water, SDW) and ‘dirty’ (3 g/L bovine serum albumin, BSA) conditions. Mean concentration (log10 CFU/mL) were calculated from direct counts. The levels of dipicolinic acid (DPA), indicating damage to the core of these spores, was also monitored using a terbium (Tb)-DPA assay for treatment 1 (peracetic acid as the active ingredient) in SDW and BSA. In SDW sporicidal treatment 3 (containing peroxymonosulphate) was the most effective against C. estertheticum spores but under ‘dirty’ (BSA) conditions sporicidal treatments 1 and 2 were more effective. A similar pattern was obtained with C. gasigenes with treatment 3 being the most effective in SDW but treatment 2 (sodium hypochlorite as the active ingredient) being more effective in BSA. The lower DPA concentrations obtained in SDW versus BSA demonstrated the protective effect of organic matter. It was concluded that meat processors should use a 5% formulation containing sodium hypochlorite, sodium hydroxide and alkylamine oxide to eliminate BPS Clostridial spores in the abattoir.

The spore coat is essential for Bacillus subtilis spore resistance to pulsed light, and pulsed light treatment eliminates some spore coat proteins

Microbial surface contamination of equipment or of food contact material is a recurring problem in the food industry. Spore-forming bacteria are far more resistant to a wide variety of treatments than their vegetative forms. Understanding the mechanisms underlying decontamination processes is needed to improve surface decontamination strategies against endospores potentially at the source of foodborne diseases or food-spoilage. Pulsed light (PL) with xenon lamps delivers high-energy short-time pulses of light with wavelengths in the range 200 nm-1100 nm and a high UV-C fraction. Bacillus subtilis spores were exposed to either PL or to continuous UV-C. Gel electrophoresis and western blotting revealed elimination of various proteins of the spore coat, an essential outer structure that protects spores from a wide variety of environmental conditions and inactivation treatments. Proteomic analysis confirmed the elimination of some spore coat proteins after PL treatment. Transmission electron microscopy of PL treated spores revealed a gap between the lamellar inner spore coat and the outer spore coat. Overall, spores of mutant strains with defects in genes coding for spore coat proteins were more sensitive to PL than to continuous UV-C. This study demonstrates that radiations delivered by PL contribute to specific damage to the spore coat, and overall to spore inactivation.

Inactivation kinetics of Geobacillus stearothermophilus spores by a peracetic acid or hydrogen peroxide fog in comparison to the liquid form

The aim of this study was to compare the sporicidal effect of the disinfectants peracetic acid (PAA) or hydrogen peroxide (H₂O₂) applied as a fog or as a liquid. The efficacy of fogging of the disinfectants was tested in a closed isolator cabinet using highly heat and chemical-resistant spores of Geobacillus stearothermophilus. Fogging of a 0.06% solution of PAA resulted in over 5-log reduction of spores in 10 min, whereas for PAA used in liquid form the same reduction was achieved in 4.5 min. The inactivation curves for fog and liquid were fitted using three different models (Linear with shoulder, Weibull, Gauss-Eyring). This showed a shoulder for the fog with an estimated length of 4.1 min, but the D values, calculated for the linear parts of the curves, were not significantly different (1.1 and 0.8 min for the PAA fog and solution, respectively). Similar results were obtained for a 12% H₂O₂ solution, albeit that H₂O₂ was less effective compared to PAA, requiring 60 min to reach 3-log reduction when applied as a fog, with an estimated shoulder of 18.5 min. Fogging of a 0.06% peracetic acid solution effectively inactivated G. stearothermophilus spores. Overall, the data show that fogging can be an effective method of applying disinfectants but that a shoulder in the inactivation curves should be considered in process design. This study provides inactivation kinetics for disinfection using PAA or H₂O₂-based fog, which can aid in selection and validation of process parameters for disinfection of contained areas by fogging.

Plasma-Activated Aerosolized Hydrogen Peroxide (aHP) in Surface Inactivation Procedures

INTRODUCTION

Hydrogen peroxide is a strong oxidant that possesses an antimicrobial activity. It has been successfully used in surface/room decontamination processes either under the form of hydrogen peroxide vapor (HPV) or of vaporized hydrogen peroxide (VHP). Aerosolized hydrogen peroxide (aHP) offers a third alternative. The technology relies on the dispersion of aerosols of a hydrogen peroxide solution often complemented with silver cations. aHP provides an inexpensive and safe approach to treat contaminated rooms but sometimes fails to achieve the 6-log10 reduction limit in the number of viable microorganisms.

METHODS

Here, we used a venturi-based aHP generator that generates 4 mm in size aerosols from a 12% plasma-activated hydrogen peroxide solution free of silver cations.

RESULTS & DISCUSSION

We could successfully and constantly inactivate bacterial growth from biological indicators containing at least 106 spores of Geobacillus stearothermophilus placed on stainless steel discs wrapped in Tyvek pouches. We could also show that the biological indicators placed at various locations in a class II biosafety cabinet were equally inactivated, showing that hydrogen peroxide aerosols migrate through HEPA filters.

CONCLUSIONS

Considering that our method for aerosol generation is simple, reproducible, and highly effective at inactivating spores, our approach is expected to serve as a relatively cost effective alternative method for disinfecting potentially contaminated rooms or surfaces.

Observations on research with spores of Bacillales and Clostridiales species

The purpose of this article is to highlight some areas of research with spores of bacteria of Firmicute species in which the methodology too commonly used is not optimal and generates misleading results. As a consequence, conclusions drawn from data obtained are often flawed or not appropriate. Topics covered in the article include the following: (i) the importance of using well-purified bacterial spores in studies on spore resistance, composition, killing, disinfection and germination; (ii) methods for obtaining good purification of spores of various species; (iii) appropriate experimental approaches to determine mechanisms of spore resistance and spore killing by a variety of agents, as well as known mechanisms of spore resistance and killing; (iv) common errors made in drawing conclusions about spore killing by various agents, including failure to neutralize chemical agents before plating for viable spore enumeration, and equating correlations between changes in spore properties accompanying spore killing with causation. It is hoped that a consideration of these topics will improve the quality of spore research going forward.

Evaluating the Sporicidal Activity of Disinfectants against Clostridium difficile and Bacillus amyloliquefaciens Spores by Using the Improved Methods Based on ASTM E2197-11

Spore-forming pathogenic bacteria, such as Clostridium difficile, are associated with nosocomial infection, leading to the increased use of sporicidal disinfectants, which impacts socioeconomic costs. However, C. difficile can be prevented using microorganisms such as Bacillus amyloliquefaciens, a prophylactic agent that has been proven to be effective against it in recent tests or it can be controlled by sporicidal disinfectants. These disinfectants against spores should be evaluated according to a known and recommended standard. Unfortunately, some newly manufactured disinfectants like Bioxy products have not yet been tested. ASTM E2197-11 is a standard test that uses stainless steel disks (1 cm in diameter) as carriers, and the performance of the test formulation is calculated by comparing the number of viable test organisms to that on the control carriers. Surface tests are preferable for evaluating disinfectants with sporicidal effects on hard surfaces. This study applies improved methods, based on the ASTM E2197-11 standard, for evaluating and comparing the sporicidal efficacies of several disinfectants against spores of C. difficile and B. amyloliquefaciens, which are used as the test organisms. With the improved method, all spores were recovered through vortexing and membrane filtration. The results show that chlorine-based products are effective in 5 min and Bioxy products at 5% w/v are effective in 10 min. Although Bioxy products may take longer to prove their effectiveness, their non-harmful effects to hospital surfaces and people have been well established in the literature.

MPLEx: a method for simultaneous pathogen inactivation and extraction of samples for multi-omics profiling

The continued emergence and spread of infectious agents is of great concern, and systems biology approaches to infectious disease research can advance our understanding of host-pathogen relationships and facilitate the development of new therapies and vaccines. Molecular characterization of infectious samples outside of appropriate biosafety containment can take place only subsequent to pathogen inactivation. Herein, we describe a modified Folch extraction using chloroform/methanol that facilitates the molecular characterization of infectious samples by enabling simultaneous pathogen inactivation and extraction of proteins, metabolites, and lipids for subsequent mass spectrometry-based multi-omics measurements. This single-sample metabolite, protein and lipid extraction (MPLEx) method resulted in complete inactivation of clinically important bacterial and viral pathogens with exposed lipid membranes, including Yersinia pestis, Salmonella Typhimurium, and Campylobacter jejuni in pure culture, and Yersinia pestis, Campylobacter jejuni, and West Nile, MERS-CoV, Ebola, and influenza H7N9 viruses in infection studies. In addition, >99% inactivation, which increased with solvent exposure time, was also observed for pathogens without exposed lipid membranes including community-associated methicillin-resistant Staphylococcus aureus, Clostridium difficile spores and vegetative cells, and adenovirus type 5. The overall pipeline of inactivation and subsequent proteomic, metabolomic, and lipidomic analyses was evaluated using a human epithelial lung cell line infected with wild-type and mutant influenza H7N9 viruses, thereby demonstrating that MPLEx yields biomaterial of sufficient quality for subsequent multi-omics analyses. Based on these experimental results, we believe that MPLEx will facilitate systems biology studies of infectious samples by enabling simultaneous pathogen inactivation and multi-omics measurements from a single specimen with high success for pathogens with exposed lipid membranes.

Variability in DPA and Calcium Content in the Spores of Clostridium Species

Spores of a number of clostridial species, and their resistance to thermal treatment is a major concern for the food industry. Spore resistance to wet heat is related to the level of spore hydration, which is inversely correlated with the content of calcium and dipicolinic acid (DPA) in the spore core. It is widely believed that the accumulation of DPA and calcium in the spore core is a fundamental component of the sporulation process for all endospore forming species. We have noticed heterogeneity in the heat resistance capacity and overall DPA/calcium content among the spores of several species belonging to Clostridium sensu stricto group: two C. acetobutylicum strains (DSM 792 and 1731), two C. beijerinckii strains (DSM 791 and NCIMB 8052), and a C. collagenovorans strain (DSM 3089). A C. beijerinckii strain (DSM 791) and a C. acetobutylicum strain (DSM 792) display low Ca and DPA levels. In addition, these two species, with the lowest average Ca/DPA content amongst the strains considered, also exhibit minimal heat resistance. There appears to be no correlation between the Ca/DPA content and the phylogenetic distribution of the C. acetobutylicum and C. beijerinckii species based either on the 16S rRNA or the spoVA gene. This finding suggests that a subset of Clostridium sensu stricto species produce spores with low resistance to wet heat. Additionally, analysis of individual spores using STEM-EDS and STXM revealed that DPA and calcium levels can also vary amongst individual spores in a single spore population.

Spore Resistance Properties

Spores of various Bacillus and Clostridium species are among the most resistant life forms known. Since the spores of some species are causative agents of much food spoilage, food poisoning, and human disease, and the spores of Bacillus anthracis are a major bioweapon, there is much interest in the mechanisms of spore resistance and how these spores can be killed. This article will discuss the factors involved in spore resistance to agents such as wet and dry heat, desiccation, UV and γ-radiation, enzymes that hydrolyze bacterial cell walls, and a variety of toxic chemicals, including genotoxic agents, oxidizing agents, aldehydes, acid, and alkali. These resistance factors include the outer layers of the spore, such as the thick proteinaceous coat that detoxifies reactive chemicals; the relatively impermeable inner spore membrane that restricts access of toxic chemicals to the spore core containing the spore's DNA and most enzymes; the low water content and high level of dipicolinic acid in the spore core that protect core macromolecules from the effects of heat and desiccation; the saturation of spore DNA with a novel group of proteins that protect the DNA against heat, genotoxic chemicals, and radiation; and the repair of radiation damage to DNA when spores germinate and return to life. Despite their extreme resistance, spores can be killed, including by damage to DNA, crucial spore proteins, the spore's inner membrane, and one or more components of the spore germination apparatus.

Reduction in the incidence of hospital-acquired MRSA following the introduction of a chlorine dioxide 275 ppm based disinfecting agent in a district general hospital

Background

Methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile are major nosocomial pathogens whose control relies on effective antimicrobial stewardship and infection control practices. This study evaluates the impact of a chlorine dioxide-based disinfectant (275 ppm) on the incidence of hospital-acquired (HA) MRSA and HA-Clostridium difficile infection (CDI) in a district general hospital.

Methods

This study was carried out from November 2009 to September 2013. From November 2009 to October 2011 sodium dichloroisocyanurate was used for routine environmental disinfection. In November 2011, this was changed to a chlorine dioxide 275 ppm based disinfectant. This product was introduced into the hospital in a phased manner with intensive training on its use provided to all nursing, nursing auxiliary and hotel services staff. The effect of this change on the incidence of HA-MRSA and HA-CDI was assessed using segmented regression analysis of interrupted time series. In addition, the potential cost savings as a result of this intervention were assessed.

Results

The HA-MRSA trend from November 2009 to October 2011 significantly increased (p=0.006). Following the introduction of the chlorine dioxide-based disinfectant there was significant decrease in the HA-MRSA trend, with the monthly incidence being reduced by 0.003 cases/100 bed days (p=0.001), equating to an average of four cases per month after 12 months of use This resulted in an annual potential cost saving of £276 000. No significant effect on the incidence of HA-CDI was observed (coefficient -0.03; p=0.873).

Conclusion

This study highlights the importance of effective environmental inanimate surface decontamination in controlling the spread of MRSA and the potential cost savings that can be achieved through decreasing HA-MRSA rates.

Disruption of the Gut Microbiome: Clostridium difficile Infection and the Threat of Antibiotic Resistance

Clostridium difficile is well recognized as the leading cause of antibiotic-associated diarrhea, having a significant impact in both health-care and community settings. Central to predisposition to C. difficile infection is disruption of the gut microbiome by antibiotics. Being a Gram-positive anaerobe, C. difficile is intrinsically resistant to a number of antibiotics. Mobile elements encoding antibiotic resistance determinants have also been characterized in this pathogen. While resistance to antibiotics currently used to treat C. difficile infection has not yet been detected, it may be only a matter of time before this occurs, as has been seen with other bacterial pathogens. This review will discuss C. difficile disease pathogenesis, the impact of antibiotic use on inducing disease susceptibility, and the role of antibiotic resistance and mobile elements in C. difficile epidemiology.

Mechanism of Sporicidal Activity for the Synergistic Combination of Peracetic Acid and Hydrogen Peroxide

There is still great interest in controlling bacterial endospores. The use of chemical disinfectants and, notably, oxidizing agents to sterilize medical devices is increasing. With this in mind, hydrogen peroxide (H2O2) and peracetic acid (PAA) have been used in combination, but until now there has been no explanation for the observed increase in sporicidal activity. This study provides information on the mechanism of synergistic interaction of PAA and H2O2 against bacterial spores. We performed investigations of the efficacies of different combinations, including pretreatments with the two oxidizers, against wild-type spores and a range of spore mutants deficient in the spore coat or small acid-soluble spore proteins. The concentrations of the two biocides were also measured in the reaction vessels, enabling the assessment of any shift from H2O2 to PAA formation. This study confirmed the synergistic activity of the combination of H2O2 and PAA. However, we observed that the sporicidal activity of the combination is largely due to PAA and not H2O2. Furthermore, we observed that the synergistic combination was based on H2O2 compromising the spore coat, which was the main spore resistance factor, likely allowing better penetration of PAA and resulting in the increased sporicidal activity.

Inactivation of Clostridium difficile spores by microwave irradiation

Spores are a potent agent for Clostridium difficile transmission. Therefore, factors inhibiting spores have been of continued interest. In the present study, we investigated the influence of microwave irradiation in addition to conductive heating for C. difficile spore inactivation in aqueous suspension. The spores of 15 C. difficile isolates from different host origins were exposed to conductive heating and microwave irradiation. The complete inhibition of spore viability at 10(7) CFU/ml was encountered following microwave treatment at 800 W for 60 s, but was not observed in the conductive-heated spores at the same time-temperature exposure. The distinct patterns of ultrastructural alterations following microwave and conductive heat treatment were observed and the degree of damages by microwave was in the exposure time-dependent manner. Microwave would therefore be a simple and time-efficient tool to inactivate C. difficile spores, thus reducing the risk of C. difficile transmission.

Decontamination Efficacy and Skin Toxicity of Two Decontaminants against Bacillus anthracis

Decontamination of bacterial endospores such as Bacillus anthracis has traditionally required the use of harsh or caustic chemicals. The aim of this study was to evaluate the efficacy of a chlorine dioxide decontaminant in killing Bacillus anthracis spores in solution and on a human skin simulant (porcine cadaver skin), compared to that of commonly used sodium hypochlorite or soapy water decontamination procedures. In addition, the relative toxicities of these decontaminants were compared in human skin keratinocyte primary cultures. The chlorine dioxide decontaminant was similarly effective to sodium hypochlorite in reducing spore numbers of Bacillus anthracis Ames in liquid suspension after a 10 minute exposure. After five minutes, the chlorine dioxide product was significantly more efficacious. Decontamination of isolated swine skin contaminated with Bacillus anthracis Sterne with the chlorine dioxide product resulted in no viable spores sampled. The toxicity of the chlorine dioxide decontaminant was up to two orders of magnitude less than that of sodium hypochlorite in human skin keratinocyte cultures. In summary, the chlorine dioxide based decontaminant efficiently killed Bacillus anthracis spores in liquid suspension, as well as on isolated swine skin, and was less toxic than sodium hypochlorite in cultures of human skin keratinocytes.

Effect of airborne hydrogen peroxide on spores of Clostridium difficile

BACKGROUND

Contamination of surfaces by spores of Clostridium difficile is a major factor influencing the spread of healthcare-associated C. difficile infection. The aim of this study was to test the effect of an automated room disinfection system that provides an aerosol of 7.5 % hydrogen peroxide (H2O2) disinfectant, on spores of two different strains of C. difficile, and to evaluate the impact of biological soiling on the efficacy of H2O2 disinfection.

MATERIAL AND METHOD

The strains used were a C. difficile PCR ribotype 027 and a C. difficile ATCC 9689. Spore suspensions of each strain were applied to ceramic tiles and exposed to aerosolized H2O2 at different locations in a test room. Biological soiling was simulated by bovine serum albumin and sheep erythrocytes. At set time points spores were recovered, plated onto Columbia 5 % sheep blood agar, and surviving bacteria were counted as colony-forming units (cfu).

RESULTS

No viable spores of either strain were recovered after a 3 h exposure to gaseous H2O2. Spores located inside a drawer showed recovery of approximately 1E5 cfu/ml for C. difficile ribotype 027 after 1 h. In the presence of organic matter, a more than fivefold log reduction compared with not exposed controls could be observed for spores of either strain tested.

CONCLUSION

Appropriate decontamination of surfaces exposed to spores of C. difficile is challenging for conventional cleaning methods. Aerosolized H2O2 delivered by automated room disinfection systems could possibly improve surface decontamination and thereby reduce transmission of healthcare-associated C. difficile infection. Also in the presence of organic matter H2O2 disinfection appears to be an effective adjunct for decontamination of environmental surfaces.

Clostridium difficile virulence factors: Insights into an anaerobic spore-forming pathogen

The worldwide emergence of epidemic strains of Clostridium difficile linked to increased disease severity and mortality has resulted in greater research efforts toward determining the virulence factors and pathogenesis mechanisms used by this organism to cause disease. C. difficile is an opportunist pathogen that employs many factors to infect and damage the host, often with devastating consequences. This review will focus on the role of the 2 major virulence factors, toxin A (TcdA) and toxin B (TcdB), as well as the role of other putative virulence factors, such as binary toxin, in C. difficile-mediated infection. Consideration is given to the importance of spores in both the initiation of disease and disease recurrence and also to the role that surface proteins play in host interactions.

Efficacy of sporicidal wipes for inactivation of a Bacillus anthracis surrogate

AIMS

To evaluate five commercially available sporicidal wipes and two disinfecting wipes for their ability to inactivate Bacillus atrophaeus spores deposited onto various material surfaces.

METHODS AND RESULTS

Decontamination efficacy of the wipes was initially tested on glass Petri dishes (150 mm diameter). Following exposure for a specified time of contact, survival of the spores was assessed by quantification of the remaining viable spores, both on the coupon surface and on the towelette itself, with efficacy quantified in terms of mean log reduction. Based on these data, five wipes were down-selected for evaluation on a larger scale, using 36 × 36 cm coupons of five different material types.

CONCLUSIONS

Results suggest that sodium hypochlorite-based sporicidal wipes were most effective, having completely inactivated the Bacillus spores on the glass Petri dish and several materials. Additionally, results demonstrate that the manufacturer-prescribed contact times for Clostridium difficile achieved a 6 log10 reduction of B. atrophaeus spores. Moreover, commercially available disinfecting wipes were not able to kill Bacillus spores as evaluated.

SIGNIFICANCE AND IMPACT OF THE STUDY

These data show the potential of sporicidal wipes for decontamination of small, contained areas of biological contamination and may help on-scene coordinators develop remediation plans following a biological terrorism event.

Best practice in healthcare environment decontamination

There is now strong evidence that surface contamination is linked to healthcare-associated infections (HCAIs). Cleaning and disinfection should be sufficient to decrease the microbial bioburden from surfaces in healthcare settings, and, overall, help in decreasing infections. It is, however, not necessarily the case. Evidence suggests that there is a link between educational interventions and a reduction in infections. To improve the overall efficacy and appropriate usage of disinfectants, manufacturers need to engage with the end users in providing clear claim information and product usage instructions. This review provides a clear analysis of the scientific evidence supporting the role of surfaces in HCAIs and the role of education in decreasing such infections. It also examines the debate opposing the use of cleaning versus disinfection in healthcare settings.

A systematic evaluation of a peracetic-acid-based high performance disinfectant

The importance of environmental contamination in the spread of healthcare associated infections (HAI) has generated a need for high performance disinfectants. Currently chlorine-based disinfectants are the products of choice, a position reflected in UK guidance. The aim of this research was to evaluate a peracetic acid (PAA) generating disinfectant to determine if it provided a realistic alternative to commonly used chlorine-based disinfectants. The European standards framework was employed in this study and enhanced where appropriate by reducing the contact times, increasing the organic and microbial challenge, and changing the organisms involved. When tested against bacteria and spores PAA provided similar or better performance than currently employed levels of chlorine. This was particularly the case in the presence of an organic challenge or dried surface contamination. The chlorine disinfectants only demonstrated superior performance in the case of fungal spores. These results suggest that PAA generating products provide an effective alternative to chlorine-based products up to 10,000 ppm free available chlorine. These products have superior performance in situations with spore borne, surface contamination and high organic challenge. In cases where filamentous fungi are a concern, high levels of PAA (>5,000 ppm) would be required to match the performance of chlorine based disinfectants.

Bacterial spore structures and their protective role in biocide resistance

The structure and chemical composition of bacterial spores differ considerably from those of vegetative cells. These differences largely account for the unique resistance properties of the spore to environmental stresses, including disinfectants and sterilants, resulting in the emergence of spore-forming bacteria such as Clostridium difficile as major hospital pathogens. Although there has been considerable work investigating the mechanisms of action of many sporicidal biocides against Bacillus subtilis spores, there is far less information available for other species and particularly for various Clostridia. This paucity of information represents a major gap in our knowledge given the importance of Clostridia as human pathogens. This review considers the main spore structures, highlighting their relevance to spore resistance properties and detailing their chemical composition, with a particular emphasis on the differences between various spore formers. Such information will be vital for the rational design and development of novel sporicidal chemistries with enhanced activity in the future.

Efficacy of "sporicidal" wipes against Clostridium difficile

BACKGROUND

Hospital-acquired infections associated with Clostridium difficile cause severe morbidity and mortality. The current control of C difficile endospores with liquid sporicides might have limited efficacy in the health care environment. Sporicidal wipes might offer additional control of surface bioburden and are now increasingly used, although there is little information about their efficacy against spores in practice.

METHODS

Ten wipes were tested for sporicidal efficacy using a recently developed 3-stage protocol that measures the ability of the wipe to remove microbial bioburden from a surface, the potential for microbial transfer from the wipe to other surfaces, and the sporicidal activity of the wipe. Scanning electron microscopy was used to visualize the association of spores with the wipe fibers, and light scattering was used to measure the size of spore aggregates released from the wipes.

RESULTS

The ability of the sporicidal wipes to remove C difficile spores from an inanimate surface ranged from 0.22 to 4.09 log(10) spores removed within 10 seconds. One wipe did not remove any spores. None of the wipes demonstrated high sporicidal activity (ie, >4 log(10) reduction) within 5 minutes of contact time, except for a control wipe soaked in 5,000-ppm sodium hypochlorite. Only one wipe demonstrated some sporicidal activity after 5 minutes, with a 1.50 and a 3.74 log(10) reduction in spore number of C difficile NCTC12727 and R20291 (ribotype 027), respectively. All but one wipe demonstrated that spores could be repeatedly transferred to other surfaces. Light-scattering data provided evidence that some wipes were able to break up spore aggregates, potentially releasing more spores onto the surface. Electron microscopy micrographs showed that spores might be loosely associated with some wipes, explaining the rapid release.

CONCLUSION

Although the use of sporicidal wipes might offer additional control of microbial burden on surfaces, current efficacy tests might be inadequate to reflect the activity of these wipes in practice. This can lead to the use of wipes that might not be appropriate for applications in the health care environment. Tighter control of labeling and appropriate efficacy tests are needed before antimicrobial wipes are released to the market.