Sporicidal Effect Research Articles

Understanding of the importance of the spore coat structure and pigmentation in the Bacillus subtilis spore resistance to low-pressure plasma sterilization

Low-pressure plasmas have been evaluated for their potential in biomedical and defense purposes. The sterilizing effect of plasma can be attributed to several active agents, including (V)UV radiation, charged particles, radical species, neutral and excited atoms and molecules, and the electric field. Spores of Bacillus subtilis were used as a bioindicator and a genetic model system to study the sporicidal effects of low-pressure plasma decontamination. Wild-type spores, spores lacking the major protective coat layers (inner, outer, and crust), pigmentation-deficient spores or spore impaired in encasement (a late step in coat assembly) were systematically tested for their resistance to low-pressure argon, hydrogen, and oxygen plasmas with and without admixtures. We demonstrate that low-pressure plasma discharges of argon and oxygen discharges cause significant physical damage to spore surface structures as visualized by atomic force microscopy. Spore resistance to low-pressure plasma was primarily dependent on the presence of the inner, and outer spore coat layers as well as spore encasement, with minor or less importance of the crust and spore pigmentation, whereas spore inactivation itself was strongly influenced by the gas composition and operational settings.

Decontamination by Persteril 36 may affect the reliability of DNA-based detection of biological warfare agents-short communication.

Persteril 36 is a disinfectant with a broad spectrum of antimicrobial activity. Because of its bactericidal, virucidal, fungicidal, and sporicidal effectiveness, it is used as a disinfectant against biological warfare agents in the emergency and army services. In case of an attack with potentially harmful biological agents, a person's gear or afflicted skin is sprayed with a diluted solution of Persteril 36 as a precaution. Subsequently, the remains of the biological agents are analyzed. However, the question remains concerning whether DNA can be successfully analyzed from Persteril 36-treated dead bacterial cells. Spore-forming Bacillus subtilis and Gram-negative Pseudomonas aeruginosa and Xanthomonas campestris were splattered on a camouflage suit and treated with 2 or 0.2% Persteril 36. After the disinfectant vaporized, the bacterial DNA was extracted and quantified by real-time PCR. A sufficient amount of DNA was recovered for downstream analysis only in the case of spore-forming B. subtilis treated with a 0.2% solution of Persteril 36. The bacterial DNA was almost completely destroyed in Gram-negative bacteria or after treatment with the more concentrated solution in B. subtilis. This phenomenon can lead to false-negative results during the identification of harmful microorganisms.

Application of electro-activated potassium acetate and potassium citrate solutions combined with moderate heat treatment on the inactivation of Clostridium sporogenes PA 3679 spores

Combined effects of moderate temperatures and the electro-activated aqueous solutions of potassium acetate and potassium citrate on the inactivation of C. sporogenes PA 3679 spores (D121°C = 1.18 min) were studied. Four types of solutions (potassium acetate with/without KCl and potassium citrate with/without KCl) were activated at 400 mA for 60 min. The oxidation reduction potential (ORP) and pH values ranged from + 417.50 to + 1043.33 mV and 3.18 to 3.47, respectively. The combination of these solutions with a moderate heat treatment (95 °C, 105 °C, and 115 °C) for different time (5, 10, 20, and 30 min) was sufficient to reach a 100% of spore destruction (inactivation) in a medium with an initial contamination level comprised between 7.0 and 7.8 log CFU/mL. The sporicidal effect of solutions was also present even if activated solutions were applied alone against spores without being combined with heat treatment. Spore morphology was determined under transmission electron microscopy and showed that there were important damages, such as rupture of spores and release of spore components in all of the treated spores. Thus, the sporicidal effect detected was the result of inactivation mechanisms of electro-activated solutions on spores. In almost all of observed micrographs, there were coreless spores, deformed spores, or debris of spores. The current investigation can be used for achieving further studies in order to better understand the mechanisms of inactivation of C. sporogenes spores by electro-activated solutions. This research article aims to study the combined effect of electro-activated potassium acetate and citrate solutions and moderate heat treatment on the viability of Clostridium sporogenes in model solutions as a non-pathogenic surrogate of Clostridium botulinum. The objective was to use hurdle technology to produce nutritious, minimally processed foods while ensuring food safety. Moreover, this approach allowed for a reduced level of sodium in canned foods since the solutions were sodium-free.

The Effect of Iodine Based Products on Unicellular Algae from Genus Prototheca

Introduction. Iodine based products have been and are still used in medicine as disinfectant or antiseptic substances, because of their bactericidal, sporicidal, protocidal and disinfection effect. Algaecide effect has been less studied and represents a strong motivation for this study. Aim. This paper is aiming to test the sensitivity to iodine based products of unicellular algae of the genus Prototheca. Such products might be used for the treatment of diseases involving these pathogens.Materials and methods. A total number of twenty-two Prototheca zopfii strains isolated from cows with mastitis or bovine shelters, were tested within this study. The algal strains were identified based on morphological characteristics (shape, size, presence of endospores), cultural (liquid and solid media characteristics) and biochemical (fermentation of sugars). Prototheca wickerhamii ATCC 16529 reference strain was also included in the evaluation. Iodinated products used were represented by: Lugol solution, iodine tincture, betadine, videne and potassium iodide. Determination of the inhibitory effect was measured by diffusion technique in agarose gel and by liquid medium dilution method. For the tincture of iodine and betadine, the inhibitory effect was also appreciated in relation with the time of contact (5, 10, 15, 30 and 60 minutes).Results. By the agar diffusion technique, it was found that inhibition zones varying sizes were correlated with the composition of those products. For the 22 Prototheca zopfii tested strains, the size of inhibition areas was within the following values (average diameter): iodine tincture 25.71 mm, betadine 26.4 mm, videne 25.61 mm, Lugol’s solution 11.33 mm and potassium iodide 11.14 mm. For Prototheca wickerhamii strain inhibition areas had the following values: betadine 26 mm, iodine tincture 24 mm, videne 24 mm, Lugol’s solution 10 mm, potassium iodine 14 mm. In case of different contact times meant to establish the algaecide effect - occurred in the first 5 minutes of contact, for both iodine tincture and betadine.Conclusion. Iodine based products tested showed inhibitory effect on algal strains. The best efficacy was found for betadine and iodine tincture (pharmaceutical/commercial products). The inhibitory effect occurs in the first 5 minutes of contact. There was no resistance phenomenon nor the presence of resistant colonies in the inhibition zones.

Sporicidal effect of amorolfine and other antimycotics used in the therapy of fungal nail infections.

Although topical antifungal therapies for treating onychomycosis are available, the cure rate is unsatisfactorily low with a simultaneously high risk of recurrence. One reason might be the formation of dormant fungal cells by the pathogen, known as spores, which can survive in the affected nail keratin, thereby evading the effect of antifungal drugs. In this in vitro study, the ability of amorolfine and four other antimycotics (ciclopirox, bifonazole, terbinafine and fluconazole) to kill microconidia of the dermatophyte Trichophyton rubrum, chlamydospores of the dermatophyte Epidermophyton floccosum and blastospores of the yeast Candida albicans was extensively studied as these fungi occur predominantly in onychomycosis. The effectiveness of all five antimycotics depended on the drug concentration and the incubation time: a concentration of 10-1000 times the minimum inhibitory concentration against growing hyphae cells is needed to exert a sporicidal action. Amorolfine and ciclopirox showed the same sporicidal efficacy and kinetics for all three varieties of spores. Both were more effective than fluconazole and bifonazole against microconidia and chlamydospores as well as slightly more potent against chlamydospores and blastospores than terbinafine after 4 days of incubation and at concentrations of ≥10 μg ml(-1). Finally, sporicidal activity on the tested strains was demonstrated for all five different antimycotics used for onychomycosis treatment.

Sporicidal Activities of Various Surfactant Components against Bacillus subtilis Spores

The sporicidal activities against Bacillus subtilis spores of surfactant components with hydrophilic and hydrophobic properties that can lead to the denaturation of various proteins comprising the spore structure were investigated. The reduction in spore numbers by each of the surfactant components bornyl acetate, geranyl acetate, pinene, p-cymene, camphene, citral, 2,3-dihydrobenzofuran, polylysine, and thiamine dilaurylsulfate at 1% was estimated at 1 to 2 log CFU/ml. The average hydrophile-lipophile balance value of surfactants with sporicidal activity causing a reduction of 1 to 2 log CFU/ml was 9.3, with a range from 6.7 to 15.8, which is similar to the values of various chemical surfactants of 9.6 to 16.7. The results also showed that the surfactants that were hydrophobic were more effective than those that were hydrophilic in killing B. subtilis spores. Furthermore, the sporicidal effect of surfactants like geranyl acetate and γ-terpinene was significantly enhanced in the presence of a germinant, because l-alanine and synergistic cofactors (e.g., K+ ions) trigger cortex hydrolysis in spores.

The impact of different process gas compositions on the inactivation effect of an atmospheric pressure plasma jet on Bacillus spores

Abstract Atmospheric plasma provides the advantages of high microbial inactivation that can be performed under ambient conditions. It is consequently regarded as potential alternative to traditional food preservation methods. In this study we systematically tested the influence of argon as plasma carrier gas with admixtures of oxygen (0–0.34 vol.%) and nitrogen (0–0.3 vol.%) towards its emission intensity of UV-C light, excited OH and N 2 -species and atomic oxygen. A mixture of argon, 0.135 vol.% oxygen and 0.2 vol.% nitrogen emitted four fold more UV photons than pure argon. However, sporicidal effects on Bacillus atrophaeus (3.1 log 10 ) and Bacillus subtilis spores (2.4 log 10 ) were found for pure argon plasma, which were similar as compared to the sporicidal effect of the plasma with highest UV-emission. To distinguish lethal effects caused by emitted UV-light and reactive species, UV-sensitive mutant spore strains (PS578 and FB122) were exposed to plasmas with different UV-emission intensities and a significant impact of UV-light on the first phase of spore inactivation was confirmed. Industrial relevance As an efficient method for the inactivation of microorganisms at low temperatures and atmospheric pressure, plasma is already commercially used for the sterilization of medical devices. The results presented in this study could be useful for a process optimization regardless if the plasma is applied for food preservation or surface decontamination. Especially the impact of emitted UV photons from the plasma on the first inactivation phase of endospores attached to surfaces, depicts a high potential of such plasmas for a rapid spore inactivation.

Sporicidal properties from surface micro-discharge plasma under different plasma conditions at different humidities

In the current study, bacterial endospores of Geobacillus stearothermophilus are exposed to the surface micro-discharge plasma for 5 min and the humidity and power consumption are varied. At the low humidity of 5.5 ± 0.5 g m−3, almost no sporicidal effect (<0.5 log) is observed. At the high humidity of 17.9 ± 0.6 g m−3, the spore reduction increases monotonically up to 3.5 log with increasing power consumption. At a humidity of 10.4 ± 0.6 g m−3, the spores are inactivated in a limited range of power consumption with a maximum reduction of ∼2.5 log. The survival curves show a single-slope decrease of the spores. The contribution of heat and UV to the sporicidal effect as well as the inactivation of spores by the short-lived species from the plasma are ruled out. The concentration of ozone, one indicator for the long-lived species, is measured and no correlation with the sporicidal effect is found. In conclusion, water-related reactive species, e.g. hydrogen peroxide, appear to be responsible for the sporicidal effect under the investigated conditions. Furthermore, condensation of water at high humidity enables the plasma-activated water containing both long-lived and short-lived reactive species to contribute to the sporicidal effect.

Ortho-phenylphenol을 주성분을 하는 훈증소독제의 Clostridium perfringens 아포에 대한 살아포 효과

본 연구는 20% ortho-phenylphenol을 함유한 훈증소독제, Fumagari <TEX>$OPP^{(R)}$</TEX>의 Clostridium perfringens (C. perfringens) 아포에 대한 살아포 효과를 평가하기 위해, French standard NF T 72-281에 따라 수행하였다. 배양 현탁액 중 C. perfringens의 아포수(N 값), 훈증소독제에 노출된 각 담체의 아포수(n1, n2, n3), 평판배지법에 의한 시험 아포 현탁액 중 아포수(N1), 여과법에 의한 시험 아포 현탁액 중 아포수(N2), 그리고 대조 담체의 회복 아포의 평균값(T 값)을 예비실험을 통해 구하였다. 또한, 훈증소독제에 노출된 C. perfringens의 감소 아포수(d 값)는, T 값, 회복액 중 아포수의 평균값(n'1) 그리고 배지의 담체에서 증식한 아포수의 평균값(n'2) 등을 이용하여 산출하였다. N 값은 <TEX>$4.4{\times}10^7spores/mL$</TEX>이었으며, n1, n2, n3은 각각 0.5N1, 0.5N2, 0.5N1 보다 높게 나타났다. 그리고 T 값은 <TEX>$4.9{\times}10^5spores/carrier$</TEX>이었다. 훈증소독제의 살아포 효과에 있어서, d 값은 4.52 이었다. 훈증소독제에 대한 프랑스 기준에 따르면, 효과적인 살균력을 갖는 훈증소독제의 d 값이 3 이상이어야 하는 것으로 규정하고 있다. 본 연구의 결과로부터, Fumagari <TEX>$OPP^{(R)}$</TEX>는 C. perfringens 아포에 대해 높은 살아포 효과를 갖는 것으로 나타나, 병원성 세균의 아포로 오염된 식품재료와 주방기기의 소독에 적용할 수 있을 것으로 사료된다. This study was performed to evaluate the sporicidal efficacy of a fumigation disinfectant containing 20% ortho-phenylphenol against Clostridium perfringens (C. perfringens) spores. In this research, efficacy test of fumigant against C. perfringens spores was carried out according to French standard NF T 72-281. C. perfringens spores working culture suspension number (N value), all the spore numbers on the carriers exposed with the fumigant (n1, n2, and n3), the number of bacterial spore suspensions by pour plate method (N1), the number of bacterial spore suspensions by filter membrane method (N2) and the mean number of bacterial spore recovered on the control-carriers (T value) were obtained from the preliminary test. In addition, the reduction number of C. perfringens spores exposed with the fumigant (d value) was calculated using T value, the mean number of bacterial spore in recovery solution (n'1) and the mean number of bacterial spore on carriers plated in agar (n'2). N value was <TEX>$4.3{\times}10^7spores/mL$</TEX>, and n1, n2, and n3 were higher than 0.5N1, 0.5N2 and 0.5N1, respectively. Additionally, T value was <TEX>$4.9{\times}10^5spores/carrier$</TEX>. In the sporicidal effect of the fumigant, the d value was 4.52log reduction. According to the French standard for the fumigant, the d value for the effective sporicidal fumigant should be over than 3log reduction. The results indicated that Fumagari <TEX>$OPP^{(R)}$</TEX> had an efficient sporicidal activity against spores of C. perfringens, then the fumigant can be applied to disinfect food materials and kitchen appliances contaminated with bacterial spores.

Synergistic sporicidal effect of ethanol on a combination of orthophthalaldehyde and didecyldimethylammonium chloride.

The objective of this study was to evaluate the potential synergistic effect of ethanol on a combination of orthophthalaldehyde (OPA) and didecyldimethylammonium chloride (DDAC) against the spores of Bacillus subtilis var. Niger. The quantitative carrier test for sporicidal testing of high-level disinfectants according to the guideline of China (Technical Standard for Disinfection 2002) was used as method. Considerable synergistic effect was observed after a 30-min treatment at 20°C. There was an augment in mean log reduction as the concentration of DDAC was increased ranging from 0·2 to 3gl(-1) in combination with 6gl(-1) OPA. Ten and 20% ethanol in combination with 6gl(-1) OPA and 2gl(-1) DDAC caused more than a 3-log reduction while either 6gl(-1) OPA, 2gl(-1) DDAC and 20% ethanol alone or a combination of two of the three agents produced less than a 1-log reduction. Further, 40-min exposure time of combination of OPA, DDAC and 20% ethanol led to greater than a 5-log reduction in spores, and no spore growth was observed following 60- and 90-min exposures. Orthophthalaldehyde (OPA) is very effective at concentrations far lower than its recommended in-use concentration of 0·5% (w/v) and is equally effective against both the gram-negative and gram-positive bacteria. However, it shows lower activity against spores. The synergistic sporicidal effect exhibited by ethanol on a combination of OPA and DDAC can be considered to enhance sporicidal activity for using in situations of sterilization, to reduce in-use concentration of OPA used alone, which may minimize its side effect. OPA may be a more satisfactory and the first-choice agent to replace glutaraldehyde (GTA) as a high-level disinfectant for medical devices.

ACTION OF NEWER DISINFECTANTS ON MULTIDRUG RESISTANT BACTERIA

BACKGROUND: Current procedures for infection control in hospital environments have not been successful in curbing the rise in infections by multi-drug-resistant (MDR) pathogens. Emergence of resistance to chemical disinfectants is increasing steadily and has been reported worldwide. So prevention of multidrug-resistant health care associated infections (HAI) has become a priority issue and great challenge to clinicians. This requires appropriate sterilization and disinfection procedures and strict adherence to protocol in infection control policy. There is a need to evaluate the efficacy of newer disinfectants which have come into the market for better control of HAI. AIMS AND OBJECTIVES: The aim of this study was to evaluate and compare disinfection efficacy of three newer disinfectants– Novacide (didecyldimethylammonium chloride and polyhexamethylene biguanide), Silvicide a strong oxidizing agent (hydrogen peroxide and silver nitrate) and Virkon, a powerful oxidizing agent (a stabilized blend of peroxygen compounds and potassium salts), pitting them against two time-honored conventional disinfectants phenol and lysol and testing them against common MDR clinical isolates, reference strains and spores. MATERIALS AND METHODS: All the disinfectants at different dilutions were tested for bactericidal efficacy by liquid suspension time-kill tests. A heavy initial microbial load was simulated by preparing bacterial inoculum. Numbers of viable cells were counted and reduction in microbial colony counts before and after disinfectant exposure was expressed as log reduction. RESULTS: Among the disinfectants, Novacide was most effective. All clinical MDR bacterial isolates and reference strains were killed within 30 seconds of exposure at 0.156% solution, whereas spores got killed after 30 minutes of exposure at 2.5% solution which is the recommended concentration. For Silvicide all vegetative bacteria were killed at 5% solution after 20 minutes contact time and at 20% solution after 10 minutes contact time where recommended concentration is 20%. Spores also were killed at 20% solution after 1 hour contact time. Virkon was very effective for vegetative bacteria at 1% solution (which is the recommended concentration), killing within 30 seconds, but for exerting sporicidal action took 2 hours contact time. The conventional disinfectant phenol has currently restricted use because of its corrosive nature and high toxicity but still is considered as standard disinfectant for microbicidal efficacy testing methods. Lysol, the most widely used hospital disinfectant was found to be least effective among the five disinfectants. Both phenol and Lysol exerted poor sporicidal effect. CONCLUSION: Novacide is the most effective disinfectant in our study. Also Silvicide and Virkon being sporicidal agent can be considered as high level disinfectant, but Virkon required much greater time exposure inappropriate for routine hospital uses including instrument disinfection, floor cleaning and waste disposal.

English

The appropriate use of biocides is essential in any vaccine production facility and their proper evaluation using standardized tests marks the first step to ensure their proper use. Quantitative suspension tests against reference and environmental isolates were carried out to evaluate the efficacy of various biocides used in the main vaccine production facility in Egypt. Several use-dilutions of the biocides were evaluated at contact times of up to 5 min in case of antiseptics and 30 min in case of disinfectants to measure the biocide activity against bacteria, fungi and spores. Standard strains were used in addition to the main bacterial isolates identified in an environmental monitoring program carried out in the same facility. Alcohol based biocides showed bactericidal and fungicidal activity but no sporicidal activity. Chlorine based compounds and glutaraldehyde showed bactericidal and fungicidal effect while, the sporicidal effects depended on the used dilution and the contact time. Hydrogen peroxide showed bactericidal, fungicidal and sporicidal activity. Quaternary ammonium compounds tested showed very weak activity in all tests. Evaluation of the biocide is an essential step to guarantee the use of the most appropriate agent in any location. &nbsp; Key words: Biocides, antiseptics, disinfectants, vaccines, Egypt.

Dual effects of single-walled carbon nanotubes coupled with near-infrared radiation on Bacillus anthracis spores: inactivates spores and stimulates the germination of surviving spores

BackgroundBacillus anthracis is a pathogen that causes life-threatening disease--anthrax. B. anthracis spores are highly resistant to extreme temperatures and harsh chemicals. Inactivation of B. anthracis spores is important to ensure the environmental safety and public health. The 2001 bioterrorism attack involving anthrax spores has brought acute public attention and triggered extensive research on inactivation of B. anthracis spores. Single-walled carbon nanotubes (SWCNTs) as a class of emerging nanomaterial have been reported as a strong antimicrobial agent. In addition, continuous near infrared (NIR) radiation on SWCNTs induces excessive local heating which can enhance SWCNTs’ antimicrobial effect. In this study, we investigated the effects of SWCNTs coupled with NIR treatment on Bacillus anthracis spores.Results and discussionThe results showed that the treatment of 10 μg/mL SWCNTs coupled with 20 min NIR significantly improved the antimicrobial effect by doubling the percentage of viable spore number reduction compared with SWCNTs alone treatment (88% vs. 42%). At the same time, SWCNTs-NIR treatment activated the germination of surviving spores and their dipicolinic acid (DPA) release during germination. The results suggested the dual effect of SWCNTs-NIR treatment on B. anthracis spores: enhanced the sporicidal effect and stimulated the germination of surviving spores. Molecular level examination showed that SWCNTs-NIR increased the expression levels (>2-fold) in 3 out of 6 germination related genes tested in this study, which was correlated to the activated germination and DPA release. SWCNTs-NIR treatment either induced or inhibited the expression of 3 regulatory genes detected in this study. When the NIR treatment time was 5 or 25 min, there were 3 out of 7 virulence related genes that showed significant decrease on expression levels (>2 fold decrease).ConclusionsThe results of this study demonstrated the dual effect of SWCNTs-NIR treatment on B. anthracis spores, which enhanced the sporicidal effect and stimulated the germination of surviving spores. SWCNTs-NIR treatment also altered the expression of germination, regulatory, and virulence-related genes in B. anthracis.

Impact of synthetic detergent on sporicidal activity in pharmaceutical facility

A continuous validation programs for disinfectants are very important in controlling microbial bioburden of environmentally controlled area. Carrier test was chosen because it is more challenging than the usual suspension test. Materials used represent floor, wall, and stainless steel surfaces. This experiment showed that detergents such as sodium dodecyl sulphate improved sporicidal effect on microorganisms even with those who demonstrated relatively high resistance to the used antimicrobial. The used surfactant enhanced the sporicidal activity within five minutes contact time with most commonly found Bacillus species in the pharmaceutical facility. However, Bacillus licheniformis spores showed greatest tolerance among studied environmental isolates.

Comparison of biocidal and sporicidal effects of spark discharge plasma and mercury-vapor low pressure lamp radiations

In this work it was shown that the inactivation micromycets spore (fungi) to hot plasma radiation of self-sustained spark discharge on air is much more effectively than UVradiation mercury-vapor lamp. Though the discharge electrical power is 15 times and UVphotons flux 430 times more for mercury lamp than for spark discharge. Discussed method inactivation is very simple.

Evaluation of peracetic acid fog for the inactivation of Bacillus anthracis spore surrogates in a large decontamination chamber

The purpose of this study was to evaluate the sporicidal (inactivation of bacterial spores) effectiveness and operation of a fogging device utilizing peracetic acid/hydrogen peroxide (PAA). Experiments were conducted in a pilot-scale 24m3 stainless steel chamber using either biological indicators (BIs) or bacterial spores deposited onto surfaces via aerosolization. Wipe sampling was used to recover aerosol-deposited spores from chamber surfaces and coupon materials before and after fogging to assess decontamination efficacy. Temperature, relative humidity, and hydrogen peroxide vapor levels were measured during testing to characterize the fog environment. The fog completely inactivated all BIs in a test using a 60mL solution of PAA (22% hydrogen peroxide/4.5% peracetic acid). In tests using aerosol-deposited bacterial spores, the majority of the post-fogging spore levels per sample were less than 1 log colony forming units, with a number of samples having no detectable spores. In terms of decontamination efficacy, a 4.78 log reduction of viable spores was achieved on wood and stainless steel. Fogging of PAA solutions shows potential as a relatively easy to use decontamination technology in the event of contamination with Bacillus anthracis or other spore-forming infectious disease agents, although additional research is needed to enhance sporicidal efficacy.

Inactivation of Bacillus anthracis Spores by Single-Walled Carbon Nanotubes Coupled with Oxidizing Antimicrobial Chemicals

In this study, we investigated the sporicidal effects of single-walled carbon nanotubes (SWCNTs) and SWCNTs combined with oxidizing antimicrobial chemicals, H₂O₂ and NaOCl, on B. anthracis spores. The results indicated that treatment with SWCNTs alone exhibited little sporicidal effect on B. anthracis spores, while treatment with H₂O₂ or NaOCl alone showed moderate sporicidal effect. The combination treatment with SWCNTs (100 μg/mL) and H₂O₂ (1.5%) or NaOCl (0.25%) exhibited much stronger sporicidal effect on the spores, compared to treatment with H₂O₂ or NaOCl alone at the same concentrations, doubling the log reduction of viable spore number (∼3.3 log vs ∼1.6 log). Such enhanced sporicidal efficiency was due to the synergistic effect contributed by the two individual antimicrobial mechanisms of SWCNTs and the oxidizing antimicrobial chemicals. The ordered sequential treatment with SWCNTs and H₂O₂ or NaOCl revealed that SWCNTs played the key role in making the spores more permeable/susceptible to chemicals. This study demonstrated the potential of combination treatment with SWCNTs and oxidizing antimicrobial agents in developing highly effective sporicidal agents/methods.

The Combined Effect of UV Irradiation and Ethanol Extract from Torilis japonica Fruit on Inactivation of Bacillus subtilis Spores

AbstractThe purpose of this study was to evaluate the synergistic sporicidal effects of the ethanol extract from Torilis japonica fruit on inactivation of Bacillus subtilis spores induced by UV irradiation at a wavelength of 254 nm. UV254 exhibited the strongest inactivation effect, with the level of spores being reduced by approximately 3.6‐ and 4.7‐log cycles, respectively, after 3 and 10 min of exposure at an irradiation distance of 15 cm. And an ethanol extract of T. japonica fruit at concentration of 1.0% reduced the spore counts by about 3.0‐log cycles for 1 h of treatment. Furthermore, a combined treatment with UV254 irradiation and 1.0% ethanol extract of the fruit produced 4.2–5.0‐log reductions of Bacillus spores at different growth stages for an exposure time of 3 min. The energy required from UV irradiation to inactivate the spores was 50% lower in the presence of 1% ethanol extract of the fruit than with UV irradiation alone.Practical ApplicationBacterial endospores, especially those of Bacillus and Clostridium genera, are the target of sterilization in various foods. The present study suggests that a combined treatment of UV irradiation and natural antimicrobial component, Torilis japonica fruit extract, can act synergistically and effectively to kill Bacillus spores and can be a potential nonthermal sterilization method for the decontamination of Bacillus spores in the food industry.

Killing Bacterial Spores with Blue Light: When Innate Resistance Meets the Power of Light

This article is a highlight of the study by Maclean et al. in this issue of Photochemistry and Photobiology describing the sporicidal effects 405 nm visible light alone on endospores of the Clostridium and Bacillus genera. 1.73 kJ cm(-2) was capable of reducing endospore colony-forming units by up to 4-log(10). These findings have never been previously demonstrated and may be incorporated into decontamination methods that span medical, military and food preparatory applications.

Sporicidal Effects of High‐Intensity 405 nm Visible Light on Endospore‐Forming Bacteria

Resistance of bacterial endospores to treatments, including biocides, heat and radiation is a persistent problem. This study investigates the susceptibility of Bacillus and Clostridium endospores to 405 nm visible light, wavelengths which have been shown to induce inactivation of vegetative bacterial cells. Suspensions of B. cereus endospores were exposed to high-intensity 405 nm light generated from a light-emitting diode array and results demonstrate the induction of a sporicidal effect. Up to a 4-log(10) CFU mL(-1) reduction in spore population was achieved after exposure to a dose of 1.73 kJ cm(-2). Similar inactivation kinetics were demonstrated with B. subtilis, B. megaterium and C. difficile endospores. The doses required for inactivation of endospores were significantly higher than those required for inactivation of B. cereus and C. difficile vegetative cells, where ca 4-log(10) CFU mL(-1) reductions were achieved after exposure to doses of 108 and 48 J cm(-2), respectively. The significant increase in dose required for inactivation of endospores compared with vegetative cells is unsurprising due to the notorious resilience of these microbial structures. However, the demonstration that visible light of 405 nm can induce a bactericidal effect against endospores is significant, and could have potential for incorporation into decontamination methods for the removal of bacterial contamination including endospores.