Reduction of microbial contamination of mobile phones using ultraviolet UV radiation and ozone

Mobile phones are known to serve as habitats and breeding grounds for microorganisms, as they provide a direct contact with human body and produce the heating effect while making long calls. Microbial analysis of the University students’ and workers’ cell phones was conducted to determine total bacterial count, numbers of mesophilic aerobic bacteria and total fungal count, before and after the disinfection procedure. The disinfection process was performed using the ozone generator 4.2 mg O3/h, the UV C (TUV 30W/G30 T8) and the UV lamp chamber. The fungi most commonly identified on mobile phones were Penicillium sp., Aspergillus sp., Ulocladium sp. whereas the dominating bacteria were Gram-positive, that is Corynebacterium, Micrococcus, Kocuria, Staphylococcus and Streptococcus. There were also recovered bacteria and opportunistic and pathogenic fungi, like Staphylococcus aureus and Trichoderma spp. The studies confirmed the bactericidal and fungicidal activity of both disinfection methods. The reduction factor (LRF) calculated for total bacterial and fungal counts indicate higher effectiveness of the ozone treatment applied.


INTRODUCTION
Currently, cell phones are the most popular mobile communication devices for business and personal use.It is estimated that in Poland approximately 85% of adults own a mobile phone.It has become a necessity of every day life, and an indispensable attribute of the modern society, which imposes changes on human behavior.The mobiles make life, work, social interaction and family contacts easier, but notably, they pose a number of new hazards as well (Czapiński and Panek, 2011).In recent years, people began to pay attention to harmful radiation emitted by mobile phones.Another dangerous factor is nomophobia -the addiction to cell phones and also the fact.Another concern raised is that this device can be the potential vector for microorganism trans-mission.It comes into a direct contact with human body and thus, microbes promptly transfer from the skin and hands to face, ears or hair.Therefore appropriate hand and body hygiene is very important.Telephones provide the conditions favorable to the growth of microorganisms as they emit heat and their body has numerous slits where dirt and sweat accumulate.Consequently, under such conditions, microorganisms have ideal place for colonization (Srikanth et al., 2009;Akinyemi et al., 2009).Presently, the sanitary condition of mobile phones is the subject of many scientific publications and is associated with the health of users.Isolated microorganisms so far, are mostly physiological microflora.However, they may favor the emergence of oppor-*Corresponding author.E-mail: bozena.nowakowicz@up.lublin.pl.tunistic infections.Therefore, it is necessary to search for the methods of safe disinfection.The activity of isopropyl alcohol was only tested so far, and also the attention to the disinfection of surfaces and hands was pointed out (Bhat et al., 2011;Singh et al., 2010;Sumritivanicha et al., 2011;Julian et al., 2012;Auchrim, 2013).The new devices encouraging disinfection, which are based on UV radiation, ozone or nanotechnology appeared in the market.However, no studies verify their effectiveness.
The objective of the research was to evaluate microbial contamination of mobile phones and to compare two methods for the elimination of microorganisms found on the mobile phone parts.

MATERIALS AND METHODS
The studies on microbial contamination of cell phones were conducted twice during the years 2011 and 2012.The research involved 60 mobile phones belonging to the workers and students.The study included 60 phones from employees and students attending classes in microbiology and related sciences.Phones for analysis were collected at the end of classes.The new mobiles were excluded from research.The disinfection process was performed with an ozone generator 4,2 mg O3/h and the UV lamp chamber.One of the techniques used for elimination of microorganisms from phone surface was ozone disinfection.It was carried out in airtight sterile bags for 15 min.Mobile phones were also placed in laminar airflow chambers equipped with UV C lamps (TUV 30W/G30 T8) for 15 min.The control group consisted of not disinfected phones.
Assessment of microbial contamination of cell phones was made using the contact plate method with appropriate selective media (OXOID LIMITED, UNITED KINGDOM).The medium Malt Extract Agar (MEA) was used for the isolation of fungi, while Triptic Soy Agar (TSA) was used for bacteria identification in accordance with the norm (PN-A-82055-19:2000P, PN-89/Z-04111/02-03).The collected samples were incubated under aerobic conditions at 37C for 24-48 h in the case of bacteria and yeast-like fungi, while filamentous fungi were incubated at 25C for 5-7 days.The outgrown bacterial and fungal colonies were counted and the microbial contamination of a cell phone was determined by the mean for each treatment group.For bacteria identification, the Gram stain test and API biochemical tests (BIOMERIEUX, Poland) were used.The mold identification procedure involved microculture methods and the use of reference keys (Krzyściak et al., 2010;Fassatiova, 1983).The obtained research results were analyzed statistically and summarized in tables.Statistical analysis was performed using analysis of variance by Statistica 10 (StatSoft, Poland).

RESULTS
The microorganisms were found on all cell phone samples.Concentrations of mesophilic aerobic bacteria and total bacterial counts on the surfaces of mobile phones investigated are shown in Tables 1 and 2, respectively.Average content of mesophilic aerobic bacteria on mobile phones ranged from 1. 1 x 10 2 up to 1.5 x 10 3 cfu/phone (Table 1).The research showed statistically significant greater number of mesophilic microorganisms on mobiles belonging to students.Mean concentration of total bacterial count on cell phones was between 1.1 x 10 2 -2.6 x 10 3 cfu/phone.Total bacterial numbers on the students' cell phones reached 6.5 x 10 2 cfu/phone and was statistically important (Table 2).
Different values were obtained for total fungal count per one phone (Table 3).Statistically significant values were determined for the samples taken from the workers' mobile phones.In all fungal isolates, the presence of anascogenic yeasts of the Candida genus was not demonstrated, whereas molds from the Penicillium, Aspergillus and Ulocladium genus were numerously represented.Among the isolated fungi, a common dermatophyte Trichoderma sp.causing cutaneous mycosis was found (Table 3).
The most frequently identified bacteria are presented in Table 4.In most cases, those were Gram-positive bacteria.The growth of bacteria from the Enterobacteriaceae family was not observed in any studied sample.The most abundant and predominant genre of microorganisms were Corynebacterium, Micrococcus, Kocuria, Staphylococcus and Streptococcus.Most of them compose the natural dermal microflora and belong to opportunistic pathogens.Nonetheless, high amounts in the host's organism with chronic or temporary immunosuppression can be hazardous for the cell phone owner.The mobile phones were also shown to harbor pathogenic bacteria S. aureus.
The present studies confirmed the bactericidal and fungicidal activity of both disinfection methods.Their effectiveness is presented in Table 5.The number of bacterial colonies on the phone before and after disinfection, obtained in the present research, was converted into common logarithm.After subtraction, from the difference of logarithms, the reduction index (RF) for the used method was calculated.The reduction factor (RF) calculated for total bacterial and fungal counts indicate higher effectiveness of ozone used as a disinfectant.Considering fungi, the reduction factor was 1.08 Lg.
The obtained logarithm exceeded, which is the evidence that 90.8% of fungi were reduced.As for total bacterial numbers, the highest value reported was 2.13 Lg.The value, however, does not fall within the 3-5 lg range, recognized as efficient bacteria disinfection (PN-EN 14885: 2007; Table 5).

DISCUSSION
Recently, attention has been drawn to the potential transfer of microbes found on mobiles and healthcare workers' palms which is likely to cause nosocomial infections in hospital (Singh et al., 1998).The present research results suggest that mobiles can act as a reservoir and source of infection.Similarly, other authors pointed out mobiles as vectors for the transmission of potential pathogens.
The studies of Ulger et al. (2009) showed that 94.5% investigated cell phones owned by healthcare workers   were contaminated with various types of bacteria, and S. aureus was found in 39.5% of all the isolates.These reports confirm the fact of pathogenic microorganisms' occurrence, and golden staph genus recovered in the present studies from the mobile surface.The differences in species composition and abundance of microorganisms isolated from the surface of mobiles of workers and students can be attributed to changes in the properties of the skin of mobile users, which appear with age.
In the process of skin aging, the changes in the permeability of the main protective element of the skinthe stratum corneum appear.Along with the advancement of age, biophysical changes occur, such as: water loss via epidermis, hydration, pH and blood circulation.The main factor contributing to the skin's surface colonization by microorganisms could play a skin reaction, persuasible alkalisation with age (Chomiczewska et al., 2010;Waller and Maibach, 2005).Substantial differentiation of microflora found on the surfaces of mobiles was also observed by Tunc and Olgun (2006) who during the research on 50 mobiles, identified 12 different types of bacteria on the those cell phones.They reported the isolation of bacteria from the following genera: S. aureus, coagulase-negative Staphylococcus (CNS), Enterococcus fecalis, Pseudomonas aureginosa, Escherischia coli, Actinobacter baumanie, Klebsiella spp.and Bacillus spp.(Trivedi et al., 2011).Al-Abdalall (2010) made analysis of 202 cell phones and showed their high contamination with fungi from the genera: Alternaria alternaria (29%), Aspergillus niger (26.9%) and Penicillium spp.(10, 47%).Similarly, the studies of Coutinho et al. (2007) indicate a high level of fungal contamination of mobiles.Authors isolated 34 species of microscopic fungi from public telephones in Brasil.
The present researches on microbial contamination of cell phones have confirmed a high mycotic contamination degree with species from Aspergillus and Penicillium genera.The abundant filamentous fungi, apart from strong allergenic properties, can induce dermal mycoses.The species Trichoderma spp., isolated in the present study belongs to opportunistic human pathogens (Chouaki et al., 2002).Molds tend to be extremely resistant to UV radiation (UV-C) therefore; it is useless in their inactivation (Otter et al., 2013).The values concerning the use of UV radiation to reduce the fungus obtained in our study also did not receive a significant amount.Given the potential for wider access of medical personnel for this type of disinfection, the extension of the duration of phones exposure to UV radiation should be considered.
In the light of the above studies, any strategy aiming at minimizing the microorganism transmission risk, including nosocomial infections, should be taken into consideration.It is essential, because antibiotic resistance is spreading and has become a new public health threat in the 21 st century (Källander et al., 2013).Bhat et al. (2011) draws attention to the fact that particular medical personnel should pay special attention to preventive measures, such as washing hands after each use of the phone, which will allow for better control of nosocomial infections.Larger contamination of mobile phones among the students in comparison to the employees, points to the need to promote such information among the students enrolled in the classes.
Personal hygiene and hand hygiene, is the most  Explanation: By the standards of the FDA / ISO for disinfection products, the main criteria for effective disinfection are: reduction of the number of bacteria by at least 3 -5 log (99.9 -99.999%) and reduction of the number of molds and yeasts by at least 1 log (90%) of the recommended disinfection period.
important procedure in preventing the transmission of human pathogenic and opportunistic bacteria (Kampf and Kramer, 2004;WHO, 2007WHO, , 2009)).Pathogen transmission and their long-lasting survival impose the implementation of strategies that indicate mandatory regular disinfection procedures of everyday household items.Preventive measures, including the use of alcoholbased disinfectants or bactericidal substances with nanosilver compounds in disinfection of different surfaces, are recommended by a number of authors (Singh et al., 1998(Singh et al., , 2010;;Ulger et al., 2009).Pulit et al. (2011) describe the nanosilver as a highly effective antimicrobial and anti-fungal agent, used for creating aseptic conditions.However, the quite toxic effect of nanosilver was observed.It can accumulate in the food chain, which creates the risk of a direct impact on living organisms.Moreover, the nanosilver can cause necrosis of human tissue and disrupt the activity of elementary components of human cells.The mobiles can be also effectively disinfected with 70% isopropyl alcohol-based means or wipes saturated in the solution of 0.5% chlorhexidine and 70% isopropyl alcohol (Brady et al., 2009).Singh et al. (2010) conducted a telephone disinfection using disin-fecting wipes moistened with 70% isopropyl alcohol.The authors obtained a reduction of bacteria on phones by 87%.The study confirmed the lack of growth of microorganisms on the surface of 47% of the phones (zero growth).However, ozone disinfection applied in the present study allowed to obtain a higher reduction of microorganisms.Disinfection is a particularly difficult challenge in the case of small areas or hard-to reachsurfaces.In such situations, some devices that enforce flow of air and simultaneously act as a disinfectant should be employed for example, an ozone generator or novel systems that combine biocidal activity of ozone and nanosilver.High effectiveness of reactive oxygen species against microorganisms, especially fungi, has been confirmed in the present research.Ozone application for restoring flood-damaged homes contributed to the reduction of total fungal numbers in air by 61,8% (Nowakowicz-Dębek et al., 2011).
The obtained research results have indicated high effectiveness of ozone disinfection, especially against filamentous fungi, which are relatively resistant to disinfecting agents.Therefore, the studies on microbial contamination of mobile phones and their disinfection methods are major issues in the broadly understood field of public health.

Conclusion
Cell phones are likely to be a source of microbial transmission, including human pathogens and that increases the risk for bacterial or fungal infection incidence.Substantial bacteriological and fungal contamination of mobile phone surfaces has been shown.Among the natural microflora of the human skin S. aureus was also isolated.The highest microbial reduction rate was observed for molds under ozone treatment and was 2.13 RF (~ 90%).

Table 2 .
Total count of bacteria on cell phones (cfu / mobile).
3Values marked with the same letters differ significantly at p≤0.05.

Table 3 .
filamentous fungi identified during the research on mobile.

Table 5 .
The level of microbial contamination after disinfection.