The bactericidal action of peroxides; an E.P.R. spin-trapping study

Antimicrobial efficacy of chlorine agents against selected oral pathogens

OBJECTIVES

Method-dependent comparison of antimicrobial agents' efficacy against oral pathogens.

MATERIALS AND METHODS

Several sodium hypochlorite solutions (NaOCl)-Perisolv®, Carisolv® and Dakin's solution-were equated with chlorhexidine (CHX) and hydrogen peroxide (H2O2) against ten oral micro-organisms related to caries and periodontitis using different minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) techniques. Agents were adjusted to the final 70 mmol/L concentration of active chlorine molecule.

RESULTS

Apart from H2O2 and the amino acids of Perisolv®, all the agents revealed an antimicrobial effect. Agar diffusion test ranked CHX (p < 0.05) as the most effective against all ten specimens, followed by the NaOCl of Perisolv® and Dakin's solution. Correspondingly, in broth microdilution on agar, CHX was the most effective in eradicating micro-organisms at 0.03 mmol/L compared with 2.2 mmol/L of Dakin's solution. In contrast, the bactericidal concentration of Dakin's solution was the most effective at 0.2 mmol/L, (p < 0.001), followed by Perisolv® (2.14 mmol/L), CHX (2.38 mmol/L) and Carisolv® (3.33 mmol/L) after 5 and 10 min in broth dilution test. In live/dead analysis, 60-min exposure to a 2-fold concentration of agents resulted in two-log Aggregatibacter actinomycetemcomitans inhibition by CHX (35 mmol/L) whilst Streptococcus mutans was more susceptible, in 0.8 and 8.8 mmol/L, after 10 min to CHX and Dakin's respectively.

CONCLUSION

Replacement of CHX with tested hypochlorite agents showed evident potential and promoted rapid antimicrobial effect.

CLINICAL RELEVANCE

Effective antimicrobial agents are crucial in controlling pathogen-induced oral infections increasing clinical possibilities to combat oral biofilms. Additionally, CHX substitution with hypochlorite agents could eliminate CHX's adverse effects.

Bioengineering liver tissue by repopulation of decellularised scaffolds

Liver transplantation is the only curative therapy for end stage liver disease, but is limited by the organ shortage, and is associated with the adverse consequences of immunosuppression. Repopulation of decellularised whole organ scaffolds with appropriate cells of recipient origin offers a theoretically attractive solution, allowing reliable and timely organ sourcing without the need for immunosuppression. Decellularisation methodologies vary widely but seek to address the conflicting objectives of removing the cellular component of tissues whilst keeping the 3D structure of the extra-cellular matrix intact, as well as retaining the instructive cell fate determining biochemicals contained therein. Liver scaffold recellularisation has progressed from small rodent in vitro studies to large animal in vivo perfusion models, using a wide range of cell types including primary cells, cell lines, foetal stem cells, and induced pluripotent stem cells. Within these models, a limited but measurable degree of physiologically significant hepatocyte function has been reported with demonstrable ammonia metabolism in vivo. Biliary repopulation and function have been restricted by challenges relating to the culture and propagations of cholangiocytes, though advances in organoid culture may help address this. Hepatic vasculature repopulation has enabled sustainable blood perfusion in vivo, but with cell types that would limit clinical applications, and which have not been shown to have the specific functions of liver sinusoidal endothelial cells. Minority cell groups such as Kupffer cells and stellate cells have not been repopulated. Bioengineering by repopulation of decellularised scaffolds has significantly progressed, but there remain significant experimental challenges to be addressed before therapeutic applications may be envisaged.

Disrupting biofilm and eradicating bacteria by Ag-Fe3O4@MoS2 MNPs nanocomposite carrying enzyme and antibiotics

In this study, novel multilayered magnetic nanoparticles (ML-MNPs) loaded with DNase and/or vancomycin (Vanc) were fabricated for eliminating multispecies biofilms. Iron-oxide MNPs (IO-core) (500-800 nm) were synthesized via co-precipitation; further, the IO-core was coated with heavy-metal-based layers (Ag and MoS₂ NPs) using solvent evaporation. DNase and Vanc were loaded onto the outermost layer of the ML-MNP formed by nanoporous MoS₂ NPs through physical deposition and adsorption. The biofilms of S. mutans or E. faecalis (or both) were formed in a brain-heart-infusion broth (BHI) for 3 days, followed by treatment with ML-MNPs for 24 h. The results revealed that coatings of Ag (200 nm) and ultrasmall MoS₂ (20 nm) were assembled as outer layers of ML-MNPs successfully, and they formed Ag-Fe₃O₄@MoS₂ MNPs (3-5 μm). The DNase-Vanc-loaded MNPs caused nanochannels digging and resulted in the enhanced penetration of MNPs towards the bottom layers of biofilm, which resulted in a decrease in the thickness of the 72-h biofilm from 48 to 58 μm to 0-4 μm. The sustained release of Vanc caused a synergistic bacterial killing up to 96%-100%. The heavy-metal-based layers of MNPs act as nanozymes to interfere with bacterial metabolism and proliferation, which adversely affects biofilm integrity. Further, loading DNase/Vanc onto the nanoporous-MoS₂-layer of ML-MNPs promoted nanochannel creation through the biofilm. Therefore, DNase-and Vanc-loaded ML-MNPs exhibited potent effects on biofilm disruption and bacterial killing.

Biotransformation of 2D Nanomaterials through Stimulated Bacterial Respiration-Produced Extracellular Reactive Oxygen Species: A Common but Overlooked Process

The biotransformation of 2D nanomaterials is still poorly understood, although their environmental fates are becoming an increasing concern with their broad applications. Here, we found that Ti₃C₂T_x nanosheets, a typical 2D nanomaterial, could be oxidized by reactive oxygen species (ROS) produced by both Gram-negative (Escherichia coli and Shewanella oneidensis) and Gram-positive (Bacillus subtilis) bacteria, with the formation of titanium dioxide (TiO₂) on the nanosheet surfaces and impairment of structural integrity. Specifically, Ti₃C₂T_x nanosheets stimulated bacterial respiration Complex I, leading to increased generation of extracellular O₂^•- and the formation of H₂O₂ and ^•OH via Fenton-like reactions, which intensified the oxidation of the nanosheets. Surface modifications with KOH and hydrazine (HMH), especially HMH, could limit bacterial oxidation of the nanosheets. These findings reveal a common but overlooked process in which oxygen-respiring bacteria are capable of oxidizing 2D nanosheets, providing new knowledge for environmental fate evaluation and future design of functional 2D nanomaterials.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.

Sterilization and disinfection methods for decellularized matrix materials: Review, consideration and proposal

Sterilization is the process of killing all microorganisms, while disinfection is the process of killing or removing all kinds of pathogenic microorganisms except bacterial spores. Biomaterials involved in cell experiments, animal experiments, and clinical applications need to be in the aseptic state, but their physical and chemical properties as well as biological activities can be affected by sterilization or disinfection. Decellularized matrix (dECM) is the low immunogenicity material obtained by removing cells from tissues, which retains many inherent components in tissues such as proteins and proteoglycans. But there are few studies concerning the effects of sterilization or disinfection on dECM, and the systematic introduction of sterilization or disinfection for dECM is even less. Therefore, this review systematically introduces and analyzes the mechanism, advantages, disadvantages, and applications of various sterilization and disinfection methods, discusses the factors influencing the selection of sterilization and disinfection methods, summarizes the sterilization and disinfection methods for various common dECM, and finally proposes a graphical route for selecting an appropriate sterilization or disinfection method for dECM and a technical route for validating the selected method, so as to provide the reference and basis for choosing more appropriate sterilization or disinfection methods of various dECM.

•

Asepsis is the prerequisite for the experiment and application of biomaterials.

•

Sterilization or disinfection affects physic-chemical properties of biomaterials.

•

Mechanism, advantages and disadvantages of sterilization or disinfection methods.

•

Factors influencing the selection of sterilization or disinfection methods.

•

Selection of sterilization or disinfection methods for decellularized matrix.

Peracetic acid-based advanced oxidation processes for decontamination and disinfection of water: A review

Peracetic acid (PAA) has attracted growing attention as an alternative oxidant and disinfectant in wastewater treatment due to the increased demand to reduce chlorine usage and control disinfection byproducts (DBPs). These applications have stimulated new investigations on PAA-based advanced oxidation processes (AOPs), which can enhance water disinfection and remove micropollutants. The purpose of this review is to conduct a comprehensive analysis of scientific information and experimental data reported in recent years on the applications of PAA-based AOPs for the removal of chemical and microbiological micropollutants from water and wastewater. Various methods of PAA activation, including the supply of external energy and metal/metal-free catalysts, as well as their activation mechanisms are discussed. Then, a review on the usage of PAA-based AOPs for contaminant degradation is given. The degradation mechanisms of organic compounds and the influence of the controlling parameters of PAA-based treatment systems are summarized and discussed. Concurrently, the application of PAA-based AOPs for water disinfection and the related mechanisms of microorganism inactivation are also reviewed. Since combining UV light with PAA is the most commonly investigated PAA-based AOP for simultaneous pathogen inactivation and micropollutant oxidation, we have also focused on PAA microbial inactivation kinetics, together with the effects of key experimental parameters on the process. Moreover, we have discussed the advantages and disadvantages of UV/PAA as an AOP against the well-known and established UV/H₂O₂. Finally, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This critical review will facilitate an in-depth understanding of the PAA-based AOPs for water and wastewater treatment and provide useful perspectives for future research and development for PAA-based technologies.

Tissue-derived decellularized extracellular matrices toward cartilage repair and regeneration

The inability of cartilage tissue to self-heal due to its avascular nature often leads to conditions such as osteoarthritis, traumatic rupture of cartilage, and osteochondrosis. The cartilage provides cushioning effects between the joints and avoids bone frictions. The extracellular matrix (ECM) of cartilage consists predominantly of collagens, elastin, proteoglycans and glycoproteins. A number of tissue engineered ECM derived biological scaffolds and matrices are available for cartilage regeneration. The decellularized tissues provide appropriate bioactive cues in the absence of cellular components, hence avoiding immunological issue. However, the decellularization process involves several cellular disruption techniques that may alter the ECM architecture affecting bioactivity. Therefore, development of cell-free cartilage biomaterials with unaltered ECM integrity and bioactivity is of paramount necessity by smart selection of modified techniques and agents. Herein, we described about various decellularization methods, agents, techniques, and their applications in tissue/cartilage decellularization. It also contemplates various difficulties and future perspectives to troubleshoot the existing obstructions in tissue-derived cartilage matrices and their applications.

Characterizing the Neuroprotective Effects of S/B Remedy (Scutellaria baicalensis Georgi and Bupleurum scorzonerifolfium Willd) in Spinal Cord Injury

The main causes of dysfunction after a spinal cord injury (SCI) include primary and secondary injuries that occur during the first minutes, hours, to days after injury. This treatable secondary cascade provides a window of opportunity for delivering therapeutic interventions. An S/B remedy (Scutellaria baicalensis Georgi and Bupleurum scorzonerifolfium Willd) has anti-inflammatory, cytoprotective, and anticarcinogenic effects in liver or neurodegenerative diseases. The present work examined the effect of S/B on injured spinal cord neurons in cultures and in vivo. S/B effectively reduced peroxide toxicity and lipopolysaccharide stimulation in both spinal cord neuron/glial and microglial cultures with the involvement of PKC and HSP70. The effect of S/B was further conducted in contusive SCI rats. Intraperitoneal injections of S/B to SCI rats preserved spinal cord tissues and effectively attenuated microglial activation. Consistently, S/B treatment significantly improved hindlimb functions of SCI rats. In the acute stage of injury, S/B treatment markedly reduced the levels of ED1 expression and lactate and had a tendency to decrease lipid peroxidation. Taken together, we demonstrated long-term hindlimb restoration alongside histological improvements with systemic S/B remedy treatment in a clinically relevant model of contusive SCI. Our findings highlight the potential of an S/B remedy for acute therapeutic intervention after SCI.

Sterilization techniques for biodegradable scaffolds in tissue engineering applications

Biodegradable scaffolds have been extensively studied due to their wide applications in biomaterials and tissue engineering. However, infections associated with in vivo use of these scaffolds by different microbiological contaminants remain to be a significant challenge. This review focuses on different sterilization techniques including heat, chemical, irradiation, and other novel sterilization techniques for various biodegradable scaffolds. Comparisons of these techniques, including their sterilization mechanisms, post-sterilization effects, and sterilization efficiencies, are discussed.

The differential effects of heat-shocking on the viability of spores from Bacillus anthracis, Bacillus subtilis, and Clostridium sporogenes after treatment with peracetic acid- and glutaraldehyde-based disinfectants

This study investigated (1) the susceptibility of Bacillus anthracis (Ames strain), Bacillus subtilis (ATCC 19659), and Clostridium sporogenes (ATCC 3584) spores to commercially available peracetic acid (PAA)- and glutaraldehyde (GA)-based disinfectants, (2) the effects that heat-shocking spores after treatment with these disinfectants has on spore recovery, and (3) the timing of heat-shocking after disinfectant treatment that promotes the optimal recovery of spores deposited on carriers. Suspension tests were used to obtain inactivation kinetics for the disinfectants against three spore types. The effects of heat-shocking spores after disinfectant treatment were also determined. Generalized linear mixed models were used to estimate 6-log reduction times for each spore type, disinfectant, and heat treatment combination. Reduction times were compared statistically using the delta method. Carrier tests were performed according to AOAC Official Method 966.04 and a modified version that employed immediate heat-shocking after disinfectant treatment. Carrier test results were analyzed using Fisher's exact test. PAA-based disinfectants had significantly shorter 6-log reduction times than the GA-based disinfectant. Heat-shocking B. anthracis spores after PAA treatment resulted in significantly shorter 6-log reduction times. Conversely, heat-shocking B. subtilis spores after PAA treatment resulted in significantly longer 6-log reduction times. Significant interactions were also observed between spore type, disinfectant, and heat treatment combinations. Immediately heat-shocking spore carriers after disinfectant treatment produced greater spore recovery. Sporicidal activities of disinfectants were not consistent across spore species. The effects of heat-shocking spores after disinfectant treatment were dependent on both disinfectant and spore species. Caution must be used when extrapolating sporicidal data of disinfectants from one spore species to another. Heat-shocking provides a more accurate picture of spore survival for only some disinfectant/spore combinations. Collaborative studies should be conducted to further examine a revision of AOAC Official Method 966.04 relative to heat-shocking.

Catalase Expression Is Modulated by Vancomycin and Ciprofloxacin and Influences the Formation of Free Radicals in Staphylococcus aureus Cultures

Detection of free radicals in biological systems is challenging due to their short half-lives. We have applied electron spin resonance (ESR) spectroscopy combined with spin traps using the probes PBN (N-tert-butyl-α-phenylnitrone) and DMPO (5,5-dimethyl-1-pyrroline N-oxide) to assess free radical formation in the human pathogen Staphylococcus aureus treated with a bactericidal antibiotic, vancomycin or ciprofloxacin. While we were unable to detect ESR signals in bacterial cells, hydroxyl radicals were observed in the supernatant of bacterial cell cultures. Surprisingly, the strongest signal was detected in broth medium without bacterial cells present and it was mitigated by iron chelation or by addition of catalase, which catalyzes the decomposition of hydrogen peroxide to water and oxygen. This suggests that the signal originates from hydroxyl radicals formed by the Fenton reaction, in which iron is oxidized by hydrogen peroxide. Previously, hydroxyl radicals have been proposed to be generated within bacterial cells in response to bactericidal antibiotics. We found that when S. aureus was exposed to vancomycin or ciprofloxacin, hydroxyl radical formation in the broth was indeed increased compared to the level seen with untreated bacterial cells. However, S. aureus cells express catalase, and the antibiotic-mediated increase in hydroxyl radical formation was correlated with reduced katA expression and catalase activity in the presence of either antibiotic. Therefore, our results show that in S. aureus, bactericidal antibiotics modulate catalase expression, which in turn influences the formation of free radicals in the surrounding broth medium. If similar regulation is found in other bacterial species, it might explain why bactericidal antibiotics are perceived as inducing formation of free radicals.

Role of operon aaoSo-mutT in antioxidant defense in Streptococcus oligofermentans

Previously, we have found that an insertional inactivation of aao_So, a gene encoding L-amino acid oxidase (LAAO), causes marked repression of the growth of Streptococcus oligofermentans. Here, we found that aao_So and mutT, a homolog of pyrophosphohydrolase gene of Escherichia coli, constituted an operon. Deletion of either gene did not impair the growth of S. oligofermentans, but double deletion of both aao_So and mutT was lethal. Quantitative PCR showed that the transcript abundance of mutT was reduced for 13-fold in the aao_So insertional mutant, indicating that gene polarity derived from the inactivation of aao_So attenuated the expression of mutT. Enzymatic assays were conducted to determine the biochemical functions of LAAO and MutT of S. oligofermentans. The results indicated that LAAO functioned as an aminoacetone oxidase [47.75 nmol H₂O₂ (min·mg protein)^–1]; and MutT showed the pyrophosphohydrolase activity, which removed mutagens such as 8-oxo-dGTP. Like paraquat, aao_So mutations increased the expression of SOD, and addition of aminoacetone (final concentration, 5 mM) decreased the mutant’s growth by 11%, indicating that the aao_So mutants are under ROS stress. HPLC did reveal elevated levels of cytoplasmic aminoacetone in both the deletion and insertional gene mutants of aao_So. Electron spin resonance spectroscopy showed increased hydroxyl radicals in both types of aao_So mutant. This demonstrated that inactivation of aao_So caused the elevation of the prooxidant aminoacetone, resulting the cellular ROS stress. Our study indicates that the presence of both LAAO and MutT can prevent endogenous metabolites-generated ROS and mutagens. In this way, we were able to determine the role of the aao_So-mutT operon in antioxidant defense in S. oligofermentans.

Silymarin protects spinal cord and cortical cells against oxidative stress and lipopolysaccharide stimulation

Contusive spinal cord injury (SCI) is a devastating event which leads to a loss of neurological function below the level of injury. A secondary degenerative process is initiated following acute SCI. This secondary cascade provides opportunities for the delivery of therapeutic interventions. Silymarin, a widely used "liver herb", is frequently used for the protection against various hepatobiliary problems. However, the effectiveness of silymarin in central nervous system (CNS), especially in spinal cord, is not firmly established. The present work evaluates the effects of silymarin and its major constituent, silybin, on oxidative stress and lipopolysaccharide (LPS) stimulation in primary neuronal/glial cell cultures and in vivo. Silymarin or silybin inhibited glial cell proliferation in a concentration-dependent manner. Furthermore, it protected glial cells against peroxide-induced reactive oxygen species (ROS) formation, ATP depletion, and cell damage. Interestingly, the inhibition of peroxide-induced ROS by silybin could be partially attenuated by inhibitors of NFκB or protein kinase C (PKC), suggesting an involvement of NFκB and PKC signaling pathways. In mixed neuronal/glial cell cultures from cerebral cortex or spinal cord, silymarin or silybin effectively attenuated peroxide-induced ROS formation, with silymarin being more effective than silybin, implicating other constituents of silymarin that may be involved. Consistently, silymarin reduced LPS-induced injures in spinal neuronal/glial cell cultures. In vivo, intrathecal administration of silymarin immediately after eliciting contusive SCI effectively improved hindlimb locomotor behavior in the rats. Taken together, silymarin or silybin shows promise in protecting the CNS cells from toxin- or injury-induced damages and might be used to treat head- or spinal cord-injuries related to free radical assault.

Comparative transcriptomic and phenotypic analysis of the responses of Bacillus cereus to various disinfectant treatments

Antimicrobial chemicals are widely applied to clean and disinfect food-contacting surfaces. However, the cellular response of bacteria to various disinfectants is unclear. In this study, the physiological and genome-wide transcriptional responses of Bacillus cereus ATCC 14579 exposed to four different disinfectants (benzalkonium chloride, sodium hypochlorite, hydrogen peroxide, and peracetic acid) were analyzed. For each disinfectant, concentrations leading to the attenuation of growth, growth arrest, and cell death were determined. The transcriptome analysis revealed that B. cereus, upon exposure to the selected concentrations of disinfectants, induced common and specific responses. Notably, the common response included genes involved in the general and oxidative stress responses. Exposure to benzalkonium chloride, a disinfectant known to induce membrane damage, specifically induced genes involved in fatty acid metabolism. Membrane damage induced by benzalkonium chloride was confirmed by fluorescence microscopy, and fatty acid analysis revealed modulation of the fatty acid composition of the cell membrane. Exposure to sodium hypochlorite induced genes involved in metabolism of sulfur and sulfur-containing amino acids, which correlated with the excessive oxidation of sulfhydryl groups observed in sodium hypochlorite-stressed cells. Exposures to hydrogen peroxide and peracetic acid induced highly similar responses, including the upregulation of genes involved in DNA damage repair and SOS response. Notably, hydrogen peroxide- and peracetic acid-treated cells exhibited high mutation rates correlating with the induced SOS response.

Effective terminal sterilization using supercritical carbon dioxide

Gentle alternatives to existing sterilization methods are called for by rapid advances in biomedical technologies. Supercritical fluid technologies have found applications in a wide range of areas and have been explored for use in the inactivation of medical contaminants. In particular, supercritical CO(2) is appealing for sterilization due to the ease at which the supercritical state is attained, the non-reactive nature, and the ability to readily penetrate substrates. However, rapid inactivation of bacterial endospores has proven a barrier to the use of this technology for effective terminal sterilization. We report the development of a supercritical CO(2) based sterilization process capable of achieving rapid inactivation of bacterial endospores while in terminal packaging. Moreover, this process is gentle; as the morphology, ultrastructure, and protein profiles of inactivated microbes are maintained. These properties of the sterilization process suit it for possible use on a wide range of biomedical products including: materials derived from animal tissues, protein based therapies, and other sensitive medical products requiring gentle terminal sterilization.

Catalase activity and the survival of Pseudomonas putida, a root colonizer, upon treatment with peracetic acid

Peracetic acid is used as a sterilant in several industrial settings. Cells of a plant-colonizing bacterium, Pseudomonas putida in liquid suspension, were more sensitive to killing by peracetic acid when they lacked a major catalase activity, catalase A. Low doses of peracetic acid induced promoter activity of the gene encoding catalase A and increased total catalase specific activity in cell extracts. Microbes present in native agricultural soils rapidly degraded the active oxygen species present in peracetic acid. The simultaneous release of oxygen was consistent with a role for catalase in degrading the hydrogen peroxide that is part of the peracetic acid-equilibrium mixture. Amendment of sterilized soils with wild-type P. putida restored the rate of degradation of peracetic acid to a higher level than was observed in the soils amended with the catalase A-deficient mutant. The association of the bacteria with the plant roots resulted in protection of the wild-type as well as the catalase-deficient mutant from killing by peracetic acid. No differential recovery of the wild-type and catalase A mutant of P. putida was observed from roots after the growth matrix containing the plants was flushed with peracetic acid.

Inactivation of enzymes within spores of Bacillus megaterium ATCC 19213 by hydroperoxides

The organic hydroperoxides t-butyl hydroperoxide, cumene hydroperoxide, and peracetic acid were found to act similarly to hydrogen peroxide in causing inactivation of enzymes within intact spores of Bacillus megaterium ATCC 19213 concomitant with mortality. Spores treated with lethal levels of the agents were germinated and permeabilized for enzyme assays. The hierarchy of sensitivities among enolase, glucose-6-phosphate dehydrogenase (G6Pdh), and pyruvate kinase to inactivation varied somewhat with the specific hydroperoxide used, possibly because of differences in the types of radicals generated. However, each agent inactivated each of the enzymes, albeit at different rates. Comparative assessments of enzyme inactivation by lethal levels of H2O2 or by moist heat showed that some enzymes, such as G6Pdh, are highly sensitive to inactivation, while others, such as ATPases, are much more resistant. The enzymes G6Pdh and aldolase were highly sensitive to hydroperoxide inactivation and also to moist heat, while pyruvate kinase was much more sensitive to hydroperoxides than to moist heat. Our overall interpretation of the findings is that hydroperoxides and moist heat can produce cumulative damage to sensitive enzymes within spores, which progressively diminishes the capacities of the cells to undergo the outgrowth required for return to vegetative life.Key words: bacterial spores, hydroperoxides, Bacillus megaterium, enzyme inactivation.

Overexpression of superoxide dismutase and catalase in immortalized neural cells: toxic effects of hydrogen peroxide

Hydrogen peroxide (H2O2) is a known toxicant which causes its damage via the production of hydroxyl radicals. It has been reported to cause both necrotic and apoptotic cell death. The present study was undertaken to evaluate the mode of H2O2-induced cell death and to assess if overexpression of catalase could protect against its toxicity. H2O2 causes cell death of immortalized CSM 14.1 neural cells in a dose-dependent manner. H2O2-induced death was associated with DNA laddering as shown by agarose gel electrophoresis. Stable overexpression of catalase by transfection of a vector containing human cDNA into these cells markedly attenuated H2O2-induced toxic effects. Transfection of a vector containing a SOD cDNA afforded no protection. These results indicate that H2O2 can lead to the activation of endonuclease enzyme that breaks DNA into oligosomes. These cells which overexpress catalase or SOD will help to determine the specific role of H2O2 or O2- in the deleterious effects of a number of toxins.

Sporicidal action of peracetic acid and protective effects of transition metal ions

Although peracetic acid (PAA) is used widely for cold sterilization and disinfection, its mechanisms of sporicidal action are poorly understood. PAA at high concentrations (5-10%) can cause major loss of optical absorbance and microscopically-visible damage to bacterial spores. Spores killed by lower levels of PAA (0.02-0.05%) showed no visible damage and remained refractile. Treatment of spores of Bacillus megaterium ATCC 19213 with PAA at concentrations close to the lethal level sensitized the cells to subsequent heat killing. In addition, PAA was found to act in concert with hypochlorite and iodine to kill spores. Antioxidant sulfhydryl compounds or ascorbate protected spores against PAA killing. Trolox, a water-soluble form of alpha-tocopherol, was somewhat protective, while other antioxidants, including alpha-tocopherol, urate, bilirubin, ampicillin and ethanol were not protective. Chelators, including dipicolinate, were not protective, but transition metal ions, especially the reduced forms (Co2+, Cu+ and Fe2+) were highly protective. The net conclusions are that organic radicals formed from PAA are sporicidal and that they may act as reducing agents for spores that are normally in a highly oxidized state, in addition to their well known actions as oxidizing agents in causing damage to vegetative cells.