Interpretation of Tailing Phenomenon of Survivor Curve and Inactivation of Virus by Plasma Exposure

Chuo Univertsity, Bunkyo-ku, Tokyo, Japan

*Corresponding Author:

Hideharu Shintani
1-10-60, Minamidaira
Hino, Tokyo 191-0041, Japan
Tel: +81425922336
E-mail: [email protected]

Received date: October 04, 2012; Accepted date:October 06, 2012; Published date: October 08, 2012

Citation: Shintani H (2012) Interpretation of Tailing Phenomenon of Survivor Curve and Inactivation of Virus by Plasma Exposure. Pharmaceut Anal Acta 3:181. doi: 10.4172/2153-2435.1000181

Copyright: © 2012 Shintani H. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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There are two questions difficult to answer. One is the tailing phenomenon of survivor curve of plasma sterilization and the other is whether plasma clusterR can inactivate bacteria and virus.

Tailing is the phenomenon illustrated in Figure 1 [1]. Many physics researcher interpreted it as being done by Moison [2], which several different kinetics may co-exist. The author deny their interpretation and considers it is due to clumping phenomenon of biological indicator (BI, Figure 2) [3] because penetration depth of gas plasma is less than 1 μm and the thickness of each bacterial spore of BI is around 1 μm. Therefore if clumped, the second layer of BI by plasma exposure will be protected with the first layer. First layer will be inactivated with first order equation as straight line of survivor curve (Figure 2), but the second or third layer delayed inactivation by protection of the first layer, so the survivor curve tailed and as a whole it is not straight line (Figure 1) [4].

Figure 1: Rate of microbial inactivation on exposure to sterilization processes. In this case, the test microorganism (generally bacterial spores) at a starting population of 10⁶ CFU (colony forming units) is exposed to the sterilizing agent under two conditions (A and B). The number of microorganisms can be determined over contact time using a direct-enumeration method. In process A, “tailing” is observed, which may not allow the extrapolation of the kill curve to a defined probability of survival (known as an SAL, sterility assurance level). In process B, the kill curve is linear, allowing extrapolation (dotted line) to an SAL of 10^-6.

Figure 2: SEM (scanning electron microscopy) photo of Geobacillus stearothermophilus ATCC 7953 inoculated on SUS.

The next question is whether plasma cluster^R, nano-e^R and so on can inactivate bacteria and virus.

The major component of plasma exposure is OH radical. The life period of OH radical is 10^-6 second and the flight distance is 30 cm/0.01 second, so only 0.003 cm can fly during life period. It is hard to analyze OH radical even though the use of radical trapping agent such as DMPO (Figure 3) because the life period of OH radical is quite short and additionally it is quite hard to set DMPO within the equipment because plasma reaction will interfere with the presence of DMPO.

Figure 3: Reactions of DMPU with O₂.- and OH. radicals. The ESR spectra of DMPO-OH and DMPO-OOH adducts are shown diagrammatically to illustrate the key difference them. The ESR spectrum of DMPO-OH adduct has 4 lines and DMPO-OH adduct has 12 lines.

OH radical can react another OH radical at the kinetics rate of 5×10⁹/M/second and produce hydrogen peroxide (H₂O₂). The reproduced H₂O₂ (OH. + OH. → H₂O₂) can then be exposed Fenton Reaction as follows:

Fe²⁺ + H₂O₂ → Fe³⁺ + OH^- + OH. K=76/M/second

Cu⁺ + H₂O₂ → Cu²⁺ + OH^- + OH. K=4.7×10³/M/second

So, the produced H₂O₂ is changed to OH. by Fenton reaction and produced OH. may react once again with OH. to produce H₂O₂ again. As this reaction continuously occurs, so OH radical is quite reactive to microorganisms (Table 1). As bacteria have Cu and Fe in their body, Fenton reaction can easily occur. On the contrary, virus has not, so Fenton reaction does not occur. This means virus is not inactivated by Fenton reaction. To confirm this, it is necessary to determine Cu and Fe in the virus body by using ICP or ion chromatography-MS.

Table 1: Comparison of sterility strength among O., OOH., OH., and H.

HEPA filter may trap virus with carrier, but not sure virus without carrier.

Bacteria charged with minus, so by charging minus, bacteria cannot into the interior of minus charged protection. On the contrary, enveloped and non-enveloped virus charged plus and minus, so hard to protect with charging [5].

As cluster^R, nano-e^R and so on promote PR of virus inactivation, but it is not always correct from the standpoint of science.

References

1. Gerald E McDonnell (2007) Antisepsis, Disinfection, and Sterilization: Types, Action, and Resistance. ASM Press, Washington DC 378.
2. Moison M, Barbeau L, Moreau S, Pelletier J, Tabrizian M, et al. (2001) Low-temperature sterilization using gas plasma: a review of the experiments and an analysis of the inactivation mechanism. Int J Pharm 226: 1-21.
3. Gueveri S, Friedman A (2007) Plasma Assited Decontamination of Biological and Chemical Agents, Springer, The Netherlands 54.
4. Sakudo A, Shintani H (2011) Sterilization and Disinfection by Plasma, Sterilization Mechanisms, Biological and Medical Applications, NOVA Science Publishers, Inc, NY, 223-227.
5. K Barry H, Gutteridge JMC (2008) Free Radicals in Biology and Medicine, Oxford University Press, 276.