Chlorine Dioxide Is a Size-Selective Antimicrobial Agent

Citation: Noszticzius Z, Wittmann M, Kly-Kullai K, Beregvri Z, Kiss I, et al. ( Chlorine Dioxide Is a Size-Selective Antimicrobial Agent Zoltn Noszticzius 0 Maria Wittmann 0 Kristf Kly-Kullai 0 Zoltn Beregvri 0 Istvn Kiss 0 Lszl 0 Rosivall 0 Jnos Szegedi 0 Patrick M Schlievert, University of Iowa Carver College of Medicine, United States of America 0 1 Department of Physics, Budapest University of Technology and Economics, Budapest, Hungary, 2 Josa Andras Hospital , Nyiregyhaza, Hungary, 3 St. Imre Hospital , Budapest , Hungary , 4 Semmelweis University , Budapest , Hungary Background / Aims: ClO2, the so-called ideal biocide, could also be applied as an antiseptic if it was understood why the solution killing microbes rapidly does not cause any harm to humans or to animals. Our aim was to find the source of that selectivity by studying its reaction-diffusion mechanism both theoretically and experimentally. Methods: ClO2 permeation measurements through protein membranes were performed and the time delay of ClO2 transport due to reaction and diffusion was determined. To calculate ClO2 penetration depths and estimate bacterial killing times, approximate solutions of the reaction-diffusion equation were derived. In these calculations evaporation rates of ClO2 were also measured and taken into account. Results: The rate law of the reaction-diffusion model predicts that the killing time is proportional to the square of the characteristic size (e.g. diameter) of a body, thus, small ones will be killed extremely fast. For example, the killing time for a bacterium is on the order of milliseconds in a 300 ppm ClO2 solution. Thus, a few minutes of contact time (limited by the volatility of ClO2) is quite enough to kill all bacteria, but short enough to keep ClO2 penetration into the living tissues of a greater organism safely below 0.1 mm, minimizing cytotoxic effects when applying it as an antiseptic. Additional properties of ClO2, advantageous for an antiseptic, are also discussed. Most importantly, that bacteria are not able to develop resistance against ClO2 as it reacts with biological thiols which play a vital role in all living organisms. Conclusion: Selectivity of ClO2 between humans and bacteria is based not on their different biochemistry, but on their different size. We hope initiating clinical applications of this promising local antiseptic. - Competing interests: ZN, MW and KKK declare competing financial interest as they are co-inventors of the European patent 2069232 Permeation method and apparatus for preparing fluids containing high purity chlorine dioxide, see also reference 13. In addition ZN is also a founder of the Solumium Ltd. The other four authors have no competing financial interest. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials. The emergence and dissemination of new antibiotic-resistant bacterial strains caused by an overuse of antibiotics [1] is a global public-health concern. Methicillin Resistant Staphylococcus aureus (MRSA) [1,2] and Carbapenem- or Extreme Drug-Resistant Acinetobacter baumannii [3,4] are only two well known examples for such bacteria attracting world wide attention. Moreover, while the number of antibiotic resistant infections is on the rise, the number of new antibiotics is declining [1,2]. As a result of such a dangerous situation, searches for new antimicrobial agents, as well as strategies including a switch from antibiotic to antiseptic therapies, whenever that is feasible, have been initiated. When treating local infections of wounds, ulcers or an infected mucous membrane, the application of antiseptics instead of antibiotics is a reasonable alternative especially because bacteria are less able to develop resistance against them [5]. Presently the majority of the antiseptics used for wounds [6] are organic compounds. The most frequently applied ones [6] are chlorhexidine (chlorhexidine digluconate), octenidine (octanidine dihydrochloride), polyhexanide (polyhexametylene biguanide) and triclosan (5-chlorine-2-(2,4dichlorphenoxy)-phenol). Notable exceptions are PVP-iodine (poly(vinylpirrolidone)-iodine complex) [6] where the active ingredient is iodine, and silver [7], both being inorganic compounds. There are some other, less used, inorganic antiseptics such as aqueous sodium hypochlorite (NaOCl), or hydrogen peroxide (H2O2) solutions, or ozone (O3) gas which have some applications in dentistry [8]. These compounds, however, are mainly used as disinfectants because they can be toxic even in low concentrations, a property seriously limiting their antiseptic applications. NaOCl, for example, one of the most commonly used components of irrigating solutions in endodontic practice, can cause poisoning and extensive tissue destruction if it is injected (inadvertently) into periapical tissues in the course of endodontic therapy [9]. H2O2 is also a double edged sword against bacteria as it also hurts living tissue [10]. Moreover, many bacteria are able to resist H2O2 as their catalase enzyme is able to decompose H2O2 rapidly [11]. Thus, beside toxicity, resistance can be also a problem even with the use of inorganic disinfectants [5]. It would be therefore reasonable to choose an antiseptic which would be free of such problems. We believe that in this respect chlorine dioxide (ClO2) may be the right choice, moreover ClO2 has other characteristic features favourable for antiseptic applications. In the last twenty or more years chlorine dioxide emerged as a new and popular inorganic disinfectant. It is often referred to as the ideal biocide [12] because of its advantageous properties. In spite of that, as far as we know, ClO2 solutions are not frequently used as antiseptic. This is because the available ClO2 solutions were more or less contaminated with other chemicals applied in its synthesis and that contamination formed a major obstacle in medical applications like treating infected wounds, for example. Since 2006, however, with the help of an invention [13], it is relatively easy to produce high purity aqueous ClO2 solutions. These solutions are already commercially available [14] and have been successfully used in dentistry [15] since 2008. Thus, it seems reasonable to ask the question whether the ideal biocide in its pure form can also be an ideal local antiseptic at the same time. Such an ideal local antiseptic should satisfy many criteria. First of all, it should be safe: it should act only locally to avoid the danger of systemic poisoning and should not inflict cytotoxic effects even in the disinfected area. In this respect, it is one of the main aims of the present work to find a reasonable answer for the following intriguing question: how is it possible that contacting or even drinking ClO2 solution is practically harmless for animals [16] and human beings [17], while the same aqueous solution can be a very effective and a rapid killer for bacteria, fungi, (...truncated)