Although most of these microbial hitchhikers won't cause you any harm, there are concerns about the spread of disease-causing or antibiotic-resistant bacteria on phones. For example, researchers in Scotland found 84% of hospital patients' phones were colonized by microbes, including pathogenic bacteria such as Staphylococcus aureus.
Most studies investigating microbial colonization of phones examine a single time point. But how does microbial colonization of phones proceed over time? I recently got a chance to find out! Two weeks ago, my cell phone of 6 years suffered a fatal fall (i.e., I dropped it). I dutifully reported to my local wireless store and left with a brand new smartphone. That night, I realized my old phone's misfortune was a golden opportunity for a longitudinal study of microbial colonization of mobile phones!
With a little more foresight, I would have tromped into the store with sterile cotton swabs to sample my new phone straight out of the box. Alas, I didn't think of it until later. But I did sample my phone within 24 hours, so the results can serve as a good "baseline" for future comparisons.
The details
Awesome lab tech Lari and I used two kinds of agar plates: (1) lysogeny broth (LB) agar and (2) trypticase soy agar (TSA) with 5% sheep's blood. We used sterile cotton swabs soaked in phosphate-buffered saline to swab the front and back of the phone (in halves). We then spread the swabs over the agar and incubated the plates at 37 degrees Celsius (98.6 degrees Fahrenheit, which is internal body temperature).
The results
Here are the plates after about 36 hours of incubation.
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| LB agar - front of phone |
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| TSA + sheep's blood agar - front of phone |
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| LB agar - back of phone |
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| TSA + sheep's blood agar - back of phone |
As expected, our baseline plates look a little sparse for microbial growth. This is probably due to minimal exposure of my new phone to people and environments, but it could also be typical of microbial colonization of phones (in the Scottish study above, 16% of samples from patients' phones didn't produce microbial growth on agar). Also, some microbes are slow growers, so 36 hours of incubation might not be long enough to see those.
Most of the colonies are small and white, which could be a number of different kinds of bacteria. There are two standout colonies, though. The LB plate of one of the swabs from the back of the phone had a beautiful cream-colored wrinkly colony (not well-captured by my shoddy phone photography skills). The TSA + blood plate of the other swab from the back of the phone had a fantastic fungal colony!
The two kinds of growth medium we used are considered "rich" media with a lot of nutrients, which are great for growing a wide range of bacteria and fungi. The TSA + blood agar is especially ideal for recovering what are called "fastidious" microbes, which have very specific nutritional requirements. For example, the fastidious pathogen Streptococcus pyogenes, which causes strep throat, scarlet fever and necrotizing fasciitis (flesh-eating disease), can make only a few amino acids and gets the others from its surroundings. TSA + sheep's blood agar is great for growing these "needy" streptococci. In addition, the red blood cells in the TSA agar can help microbiologists identify bacterial species. Certain bacteria lyse red blood cells (hemolysis) and leave a little clear zone around their colonies on blood agar plates. In this case, I didn't see any zones of hemolysis, so no luck there!
I'm looking forward to sampling my phone again in a couple of weeks to see how the microbial colonization progresses. How many microbial friends will my phone add to its network? Stay tuned for part two! In the meantime, feel free to leave comments and questions!
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