Gas Plasma Sterilization in Microbiology: Theory, Applications, Pitfalls and New Perspectives | Book
"a nice state of the art compilation" (Doodys)
Caister Academic Press
Hideharu Shintani and Akikazu Sakudo
Chuo University, Tokyo, Japan and University of the Ryukyus, Nishihara, Japan; respectively
viii + 158
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Gas plasma is the fourth state of matter, alongside solid, liquid, and gas. There are many naturally occurring events and man-made products related to gas plasma including: aurora, thunderstorms, high-intensity discharge headlamp bulbs, oxonizers, semiconductors, and solar battery panels. A gas plasma is generated by removing electrons from a gas, e.g. N2
, to produce a highly excited mixture of charged nuclei and free electrons. It has enormous potential as a broad spectrum antimicrobial sterilization procedure with applications in medical, industrial and agricultural settings (e.g. decontamination of medical instruments). A major advantage is the shallow penetration of gas plasmas: only ~10-20 nm from the surface thereby minimising damage to the material being sterilized. An important obstacle to overcome is the 'understanding-gap' between the engineering researchers who are developing the gas plasma sterilization technology and the microbiologists who aim to fine tune it for their needs. This timely volume aims to bridge that gap, permitting engineers and microbiologists to develop more coherent multidisciplinary strategies.
The book opens with introductory chapters that explain the background and principles of gas plasma sterilization and outline the possible mechanisms of action. Requirements for achieving the 'gold-standard' sterilization level i.e. a sterility assurance level (SAL) of 10-6, is also covered. The next eight chapters cover applications of this technology: these range from the inactivation of spores and endotoxins to inactivation of viruses and seed-borne plant pathogens. The final chapters tackle sterilization validation (from several ISO documents), common data-interpretation errors and speculate about future trends.
This book is an indispensable reference for students, microbiologists, engineers, and laboratory scientists interested in sterilization and decontamination.
"The purpose is to present the current status of gas plasma technology for sterilization and disinfection. These worthy objectives are well met by this book .. a nice state of the art compilation ... You will want this book if this is your area of interest." from Doodys
"of particular interest to (those) involved in sterilization and disinfection, whether they are students, researchers, lab personnel, or engineers" from SIMB News
Table of contents
Gas plasma sterilization offers enormous potential as a broad spectrum antimicrobial procedure. In this chapter we explain the types of errors that result from the 'understanding-gap' between the engineering researchers who are developing the gas plasma sterilization technology and the microbiologists who aim to fine tune it for their needs. Future initiatives to exploit this powerful technology would benefit from adopting multi-disciplinary approaches, involving close collaboration between microbiologists, chemists and engineering researchers.
2. Theoretical Background and Mode of Action of Gas Plasma Sterilization
In this chapter theoretical background and potential mode of action of gas plasma sterilization are described. Nowadays, gas plasma sterilization is widely utilized for sterilization of spores. Because spores are more tolerant than vegetative bacterial cells, bacterial endospores are used as the biological indicator (BI). Geobacillus stearothermophilus ATCC 7953 is generally used as the BI for gas plasma sterilization. Gas plasma sterilization penetration is quite shallow, ie., ~ 10-20 nm from the surface, so it is easy to achieve a sterility assurance level (SAL) of 10-6 and material/functional compatibility compared with alternative sterilization procedures. Simultaneous achievement of a SAL of 10-6 and material/functional compatibility will be discussed in detail in Chapter 3.
3. Concomitant Achievement of a Sterility Assurance Level of 10-6 with Material and Functional Compatibility by Gas Plasma Sterilization
In this chapter, we discuss the importance of attaining a sterility assurance level (SAL) of 10-6 while maintaining material/functional compatibility. Simultaneous achievement of both these factors is required in ISO 14161 and for sterilization validation. Because the level of penetration achieved by gas plasma sterilization is quite shallow, at around 10-20 nm from the surface, the procedure kills only one layer of bioburden but readily maintains material and functional compatibility. In reality, there is an absence of bioburden that form multi-layer clumps in healthcare products. Thus, gas plasma treatment easily displays material/functional compatibility whilst achieving a SAL of 10-6 due to its low temperature of operation and shallow penetration.
4. Current Progress in Advanced Technology of Nitrogen Gas Plasma for Remote Sterilization and Clarification of Sterilization
Hideharu Shintani, Naohiro Shimizu, Yuichiro Imanishi, Akikazu Sakudo, Takuya Uyama and Eiki Hotta
In this chapter, we will introduce the advanced technology for remote sterilization by exposure to nitrogen gas plasma, which is generated by a pulsed power source. Sterilization was best achieved using nitrogen gas plasma at a relative humidity (RH) of 0.5%. Furthermore, sterilization efficiency was directly correlated with the levels of OONO•- (peroxynitrite anion radical). These results suggest that OONO•- is a major factor in the case of remote sterilization by nitrogen gas plasma.
5. Current Progress in the Inactivation of Endotoxin and Lipid A by Exposure to Nitrogen Gas Plasma
Nitrogen gas plasma treatment has sporicidal activity as well as the ability to inactivate endotoxins and lipid A. The mechanism of nitrogen gas plasma sterilization may include synergistic effects involving free radicals (e.g. OH, NO or OONO radicals) and metastable species (i.e., metastable states of N2 or O2). Exposure to nitrogen gas plasma caused no discernable deterioration in the functional compatibility of various materials under investigation. Based on these findings, nitrogen gas plasma sterilization is a promising method for the sterilization of medical devices.
6. Current Progress in Advanced Research into Tetrodotoxin Inactivation by Gas Plasmas
Toshihiro Takamatsu, Hidekazu Miyahara, Takeshi Azuma and Akitoshi Okino
This study treated tetrodotoxin (TTX) solution with non-thermal multi-gas plasma and analyzed its decomposition by liquid chromatography coupled with electrospray time-of-flight mass spectrometry. The TTX signal in the mass spectrum was reduced to different levels by plasma irradiations using various gases. Nitrogen plasma exhibited the optimal capability for TTX decomposition, followed by oxygen, argon, and carbon dioxide plasmas. The TTX concentration decreased 100-fold after 10 min treatment with nitrogen plasma. To better understand the TTX degradation process, plasmas of five different gases were generated by a multi-gas plasma jet. The OH radicals and ozone molecules formed at the solution interface were then measured by electron spin resonance and photometry. The largest amount of ozone (64 µM at 15 s) and OH radical (130 µM at 30 s) were generated by oxygen and nitrogen plasma, respectively. We concluded that the generated reactive oxygen species such as OH radicals and ozone contribute to TTX degradation.
7. Current Progress in Advanced Research into Fungal and Mycotoxin Inactivation by Cold Plasma Sterilization
Pervin Başaran Akocak
Growth of fungi can cause physico-chemical spoilage, deterioration, nutritional and organoleptic property losses in food and feed commodities. Furthermore, mycotoxins produced by fungi are tremendous food safety and economic concern, and the maximum contamination levels are regulated by the international organizations. Mycotoxin control strategies include pre- and post-harvest detoxification approaches. Currently available methods are not sufficient for the full elimination or decontamination of mycotoxins. Mild non-thermal disinfection methods, which aim at actively improve the storability of goods and preserve the quality parameters of the product during post-harvest storage are continuously sought by the food industry. Recent studies indicate that application of plasma is among the promising, gentle non-thermal technologies and a new tool for the prevention and decontamination of fungal development and mycotoxin contamination while improving storability of food commodities during post-harvest storage.
8. Current Progress in the Sterilization of Spores and Vegetative Cells by Exposure to Gas Plasma: Sterilization, Disinfection and Antimicrobial Activity
In general, spores are more tolerant than vegetative cells against sterilization and disinfection. Thus, spores are generally used as the biological indicator (BI), which should correspond to the microorganism most tolerant to the targeted sterilization process (ISO 11138-1, ISO 14161). Geobacillus stearothermophilus ATCC 7953 was therefore selected as the BI for gas plasma sterilization because its spores are the most tolerant of the tested microorganisms. In this chapter, the relationship between BI and ISO, and their respective importance for validation of sterilization are described in detail.
9. Current Progress in Advanced Research into the Inactivation of Fungi and Yeasts by Gas Plasma
Recently, the risk level of fungi has been increased in human health, food safety, agriculture, and ecosystem. Efficient, eco-friendly, and long-lasting control tools for fungal diseases and contaminants are needed more than ever, and plasma has been explored as a candidate tool satisfying these criteria. In this chapter, studies on antifungal activity of plasma are summarized. Numerous studies have demonstrated that plasma treatment can efficiently inactivate fungal spores and disinfect human tissues, paper, fabrics, crop seeds, plant leaves, and foods. Plasma generated reactive species as possible fungicidal factors, may destroy or degenerate fungal cell wall and consecutively damage cell membrane and internal components. However, more experimental studies, particularly in vivo, examining antifungal effects of plasma are still required for proving the potentiality of plasma in fungal disease control. In addition, mechanisms of fungal sterilization by plasma should be elucidated in order to produce useful information applicable to optimization of plasma sterilization technology.
10. Current Progress in Advanced Research into the Inactivation of Viruses by Gas Plasma: Influenza Virus Inactivation by Nitrogen Gas Plasma
Recently, the potential of gas plasma technology for disinfection and sterilization has been exploited. The effective inactivation of bacteria, fungi, viruses as well as toxins by gas plasma exemplifies the broad application of this technology. However, information concerning the effect of gas plasma on microorganisms and their biomolecules, as well its mechanism of action, remain somewhat limited. Here, we focus on the inactivation of viruses by gas plasma, for which very few studies have been reported in the literature. This chapter will introduce our recent investigation of N2 gas plasma, produced by applying a short high-voltage pulse using a static induction (SI) thyristor power supply, which inactivates influenza virus. The biological significance of changes to the virus induced by gas plasma treatment will also be discussed.
11. Current Technology and Applications of Gas Plasma for Disinfection of Agricultural Products: Disinfection of Fungal Spores on Citrus unshiu by Atmospheric Pressure Dielectric Barrier Discharge
Yoshihito Yagyu and Akikazu Sakudo
In the field of agricultural and food processes, the development of safe, high-quality disinfection methods that do not rely on chemical treatment is a promising approach for preventing food poisoning caused by pathogens such as fungi and bacteria. Recently, information has accumulated showing the potential of gas plasma as a novel food disinfection technology. In this chapter, to highlight recent advances in gas plasma technology for applications in food disinfection, we introduce our studies on the disinfection of Penicillium digitatum spores on Citrus unshiu by atmospheric pressure dielectric barrier discharge (APDBD). Future perspectives of this technology will also be discussed.
12. Current Progress in Seed Disinfection by Gas Plasma: Disinfection of Seed-borne Fungi and Bacteria by Plasma with Alternating Current High Voltage Discharge
Terumi Nishioka, Tomoko Mishima, Yoichi Toyokawa, Tatsuya Misawa and Akikazu Sakudo
Seed-borne pathogens are one of the most important causative agents of plant diseases and prevent healthy growth, resulting in the reduction of marketable and profitable crops. Currently, treatments with hot water and air have been used for disinfection of seeds; however, these methods are time-consuming and sometimes damage seeds. Recent studies have shown the potential of gas plasma technology for disinfection of seeds. As short plasma treatments have achieved successful disinfection of seed-borne fungi and bacteria without seed damage, this innovative technology can facilitate rapid and safe disinfection of seeds. This chapter will outline our recent studies on disinfection of seed-borne fungi and bacteria by plasma with alternating current high voltage discharge and discuss the future perspectives for seed disinfection made possible by plasma technology.
13. Validation of Gas Plasma Sterilization (Importance of ISO documents, ISO TC 198 and 194).
ISO 11138-1 and ISO 14161 are the major documents to follow for biological indicator (BI) manufacturers and BI users, respectively. Based on these ISO documents, the spores of Geobacillus stearothermophilus ATCC 7953 are used for BI of gas plasma sterilization. In this chapter, the importance of following ISO documents for sterilization validation in the case of gas plasma exposure will be introduced.
14. Misinterpretation of Microbiological Data on Gas Plasma Sterilization: Avoiding the Pitfalls.
In this chapter, we discuss avoidance of clumping, tailing phenomena, and methods for attaining a SAL of 10-6 using a biological indicator (BI). As tailing of a survivor curve is often caused by clumping of the BI, appropriate techniques and confidential know-how to avoid such clumping is required. When such a tailing phenomenon is observed, a SAL of 10-6 cannot be attained, and therefore no D value (decimal reduction value) can be determined and the exposure time for a 9 or 12 log reduction remains undefined. The D value must be determined from the straight line of a 9 log or 12 log reduction survivor curve, and there can only be one D value per microorganism; there is never more than one D value per one microorganism.
15. Future Perspectives and Trends in Gas Plasma Sterilization
Gas plasma sterilization has a shallow penetration depth of approximately 10-20 nm. Thus, material and functional compatibility can be easily attained. Sterility assurance of a 12 log reduction is not always required of BI users (ISO 14161). Indeed, a 12 log reduction is quite difficult to achieve with the current gas plasma process, because a tailing phenomenon in the survivor curve can occur due to clumping of the biological indicator. Similarly, a 6 log reduction from 106 CFU/carrier to a SAL of 100 is also difficult to attain as is often seen in the engineering research. Nonetheless, a 12 log reduction is required in sterilization validation studies for BI manufacturers according to ISO 11138-1. However, simultaneous attainment of material/functional compatibility is not required of BI manufacturers in ISO 11138-1 because there are no materials being tested. When using the overkill method, a 12 log reduction is required together with material/functional compatibility for BI users according to ISO 14161. To achieve this requirement, deeper penetration of gas plasma sterilization will be needed in the future, but the penetration depth must be limited in order to maintain material/functional compatibility.
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(EAN: 9781910190258 9781910190265 Subjects: [microbiology] [bacteriology] [virology] [medical microbiology] [environmental microbiology] )