Staphylococcus Aureus Isolated from Mobile Screens

Authors: Aastha Acharya


Today, mobile phones have become one of the most indispensable accessories of professional and social life. Although they are usually stores in bags or pockets, mobile phones are handled frequently and held close to the face. Mobile phones are being used extensively in hospital settings. They are commonly handled irrespective of the cleanliness of hands and rarely disinfected, thus may harbor pathogenic bacteria. The constant handling of the phone by different users exposes it to an array of microorganisms, and makes lit a good carrier for microbes, especially those associated with the skin resulting in the spread of different microorganisms from user to user. Research has shown that the mobile phone could be a health hazard with tens of thousands of microbes living on each square inch of the phone.

Staphylococcus aureus has received considerable attention because of the role of this organism as a nosocomial pathogen especially in immune-compromised host. It is a Gram positive eubacterium that is found on the surfaces of the human skin and mucous membranes. It is an opportunistic pathogen in humans and animals and is one of the most frequent sources of hospital and community acquires infections. It is responsible for variety of human syndrome, osteomyelitis, endocarditis, pneumonia, urinary tract infections, gastroentirits. Nasal carriage of S. aureus occurs in 20-50% of human beings.

The combination of constant handling with the heat generated by the phones creates a prime breeding ground for many microorganism that are normally found on skin. Various pathogenic microbes associated with tuberculosis, meningitis, pneumonia, tonsillitis, peptic ulcers, genial tract infections, skin infections had been identified in mobile phones. The main reservoir of S. aureus is the hand from where it is introduced into food during preparation. Hand serves as a major vehicle of transmission of various microbes including the enteric species.

Isolation and Identification

For the isolation of S. aureus , selective media, Mannitol Salt Agar (MSA) or SM1 10 can be used. The selective media has an inhibitory agent that favors the growth of certain bacteria by inhibiting others. MSA contains an additional indicator for monitoring mannitol fermentation. It contains a high concentration (about 7.5%-10%) of salt (NaCl), making it selective for Gram-positive bacteria since this level of salt is inhibitory to most other bacteria. It is also a differential medium for mannitol-fermenting staphylococci, containing carbohydrate mannitol and the indicator phenol red, a pH indicator for detecting acid produced by mannitol-fermenting staphylococci. Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase-negative staphylococci produce small pink or red colonies with no colour change to the medium. [4] If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow.

For the identification of S. aureus, various tests can be performed. The tests include Gram’s stainig, colony morphology, different biochemical tests such as oxidative-fermentation (OF) test, coagulase test, oxidase test and catalase test.

Overview of various tests

Oxidative-Fermentation test: It is used to distinguish between aerobic and other sealed with paraffin which is anaerobic. Growth of the medium is either by utilizing tryptone which results in an alkaline reaction, dark blue color, or by utilizing glucose, which results in the production of acid, turning bromothymol blue to yellow. It being facultative anaerobic, it produces acid in both of tubes. It is a fermentative.

Coagulase test: The main principle of this test is to determine the ability of an organism to clot the plasma by converting fibrinogen to fibrin by the action of enzyme coagulase produced by S. aureus. The test is used specifically to differentiate species within the genus Staphylococcus. S. aureus is usually coagulase positive whereas S. epidermidis and S. saprophyticus are coagulase negative. A positive coagulase test is the final diagnostic criterion for the identification of Staphylococcus.

Catalase test: This test is to demonstrate the presence of catalase, an enzyme that catalyses the release of oxygen from hydrogen peroxide. Catalse, a hemeprotein is present in most cytochrome containing aerobic and facultative anaerobic bacteria with the main exception of Streptococcus species. It is used to differentiate those bacteria that produce an enzyme catalase, such as Staphylococcus.

Oxidase test: The basic principle of this test is to determine the presence of oxidase enzyme in bacteria that will catalyze the transport of electrons between electron donors in the bacteria and a redox dye tetramethylene-p-phenylene-diamine. S. aureus gives an oxidase test negative because they are unable to produce oxidase enzyme.

Patterns of Staphylocccus aureus isolated from different mobile phones

Total of fourteen samples were taken for the experiment. From the 14 samples, 5 belonged to the health workers and rest belonged to the college students.

From the total of 14 mobile phones used by health workers and students, the mobile phones of students were comparatively found to be more contaminated with S. aureus. Average number of Staphylococcus colony in MSA was found to be 386.25 and 367.14 of health worker and lab students respectively. In total, 92.85% mobile phones were more contaminated while rest of them were not contaminated with S. aureus. Mobile of health workers were less contaminated with 40.4% than the mobile phones of lab students with 93.62%. Among the 56 colonies of S aureus, subculture on MSA plate allowed the identification of 31 colonies of S. aureus by morphological and standard biochemical test.

Profession of mobile user Average number of organisms on MSA plate % of S. aureus occurrence % of coagulase negative Staphylococcus spp Average number of S. aureus isolated
Health worker 386.25 40.04 12.5 154.75
Student 367.14 93.62 26.08 343.71


Mobile phones can get contaminated and inhabited by microorganisms not only non-pathogenic that include our normal flora like the isolated Staphylococcus aureus, but also pathogenic organisms. Contamination of mobile phones varies among itself according to the place, areas and the personal hygiene of individual. The resistance of organism is increasing day by day and mobile phones are one of the devices which are not regularly cleaned or maintained. Taken as a whole, it is observed that our daily used mobile phones carry many pathogens including multi drug resistant organism as well.

Although statistically not significant, the contamination of S. aureus in mobile phones of lab students is found to be more than in health workers because according to them, health workers deal with the patients by using gloves and additionally wash their hands properly; whereas, lab students do not use gloves during lab woks, also might not wash their hands properly and more exposed to the microorganisms. Due to these common resources, contamination is resulted more in lab students than in health workers.


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About Author / Additional Info:
I am an undergraduate student of Microbiology from Kathmandu. I am interested in molecular biology. I aim to keep myself updated with the recent happenings in science field. I am intrigued by the discoveries and researches.