by Jyoti Souza

8 March 2025

Abstract

Keyboards collect bacteria from their users and surroundings, making them a potential hotspot for microbial diversity. This study examines the differences in bacterial diversity between a personal keyboard, used by a single individual, and a community computer, shared by multiple users. Swab samples were taken from both keyboards and analyzed to identify bacterial presence. The results showed that the community computer had a greater variety of bacteria, likely due to frequent contact with multiple users and different environments. In contrast, the personal keyboard had fewer bacterial types, primarily those associated with its main user. These findings highlight how shared surfaces contribute to microbial transmission and emphasize the importance of hygiene when using communal devices.

Introduction

Keyboards are frequently used surfaces that can collect bacteria from our hands and surroundings. Research has shown that shared objects like doorknobs, phones, and keyboards can hold a variety of bacteria, including some that could be harmful (Eisenberg, 2020). The number and types of bacteria on a keyboard can depend on how often it's used, who is using it, and how clean their hands are.

Surfaces touched by many people tend to have a wider range of bacteria because each person carries millions of different types of bacteria  (USDHHS, 2015). On the other hand, personal keyboards might have fewer types of bacteria but a higher concentration of ones specific to their owner. Based on this, we predict that the community computer will have a greater variety of bacteria compared to the personal keyboard since more people use it and introduce different microbes.

To test this, we took bacterial swabs from both a personal keyboard and a community computer, grew the bacteria in a lab, and compared the results. Understanding the bacteria on shared surfaces can help highlight the importance of cleaning and hygiene, especially in public spaces.

Materials & Methods

To compare the bacterial diversity of a personal keyboard versus a shared community computer, we used sterile swabs, nutrient agar plates, sterile water, and a marker to label our samples.

Each sample was placed on a separate agar plate rather than dividing a single plate in half. Each of us selected a specific letter or symbol on the keyboard to swab—I swabbed the left side of the space bar, while others chose different keys or symbols. We moistened the sterile swabs with water and carefully collected samples—one from a personal keyboard and another from a shared computer. To prevent contamination, we only lifted the Petri dish lid slightly while transferring bacteria onto the agar, using a zigzag motion for even distribution. Once done, we quickly sealed the plates and disposed of the used swabs in a biohazard container.

We let the plates incubate at room temperature for about a week. When we checked back, we analyzed the bacterial growth, paying attention to color, texture, size, and colony patterns. To ensure accuracy, we compared our findings with classmates who had tested different keys. We also counted the number of distinct bacterial colonies and used a diversity formula to quantify the differences between the two keyboards.

By collecting and analyzing data as a group, we gained a clearer picture of how bacteria spread on shared devices and how microbial diversity varies between personal and communal spaces.

Step-by-step Procedures:

1. Gather a Petri plate with nutrient agar, two sterile cotton swabs, sterile water, and a marking pen.
2. Use the marking pen to divide the bottom of the Petri plate into two sections and label them based on the sampling locations.
3. Moisten a sterile swab with sterile water and swab the surface of a personal keyboard, focusing on frequently touched keys.
4. Use a new sterile swab to collect a sample from the community computer keyboard.
5. Slightly lift the lid of the Petri plate (no more than an inch) and streak the swab across the agar in a zigzag motion in the assigned section.
6. Close the lid immediately to prevent contamination.
7. Dispose of used swabs in the biohazard container with the stick end showing and wash hands thoroughly.
8. Place the Petri plate in the designated lab box for incubation at room temperature for about a week.
9. After a week, retrieve the Petri plate and examine the bacterial growth in each section.
10. Observe and record characteristics of the bacterial colonies, such as color, texture, size, shape, and growth patterns.
11. Compare results with classmates who sampled similar surfaces.
12. Decide as a group how to count colonies without bias and record the number of different colony types.
13. Use the provided formula to calculate bacterial diversity for each surface.
14. Contribute findings to the class dataset for comparison.

Results

Fig. 1: Class’s datasets showing the diversity of bacteria colonies from Professor Deacon’s personal laptop keyboard, which shows us a small quantity of colonies

Fig. 2: Class’s datasets showing the diversity of bacteria colonies from MCTC’s public computer lab keyboard, which shows us a greater number of colonies.

Species Descriptions:

A: Punctiform, flat, white, off-white cream, shiny

B: Moderate, flat, round, entire

C: Small off-white cream, round, raised, circular margin

D: Large, flat, scalloped

E: Large, vaseline-colored, smooth, umbinate, round, undulate

F: Punctiform, colorless, dry, flat

G: Yellow, kind of convex, punctiform

H: Moderate, irregular, undulate, flat

I: Convex, whitish-luish, round

J: Small yellow, crateriform, scalloped

K: Punctiform, white, smooth, raised, round, entire

L: Large, irregular, scalloped

M: Moderate, smooth, wet, bullseye

Discussion

To look at species diversity in the samples, we used the Shannon-Wiener Index (H) for both the Personal and Public datasets. This index helps measure how many different species there are and how evenly they’re spread out. A higher number means more diversity. We also calculated the maximum possible Shannon diversity (Hmax) and equitability (EH) to see how balanced the species distribution was.

For the Personal sample, we found the Shannon-Wiener Index to be 1.81, while the Public sample had a lower value of 1.48. This means the Personal sample had more species variety, while the Public sample had certain species that were more dominant.

The highest possible Shannon diversity (Hmax) was 2.56 for both datasets. Equitability (EH), which shows how evenly the species were spread out, was 0.70 for the Personal sample and 0.58 for the Public sample. This suggests that the species in the Personal sample were more evenly distributed, while the Public sample had a few species taking over.

My personal sample had a low diversity score (0.57), meaning one species was way more common than the others. The equitability (0.52) shows that the species weren’t spread out evenly. On the other hand, the public sample had a higher diversity score (1.48) and was more balanced (0.92), meaning there was a better mix of species. This suggests that my public sample had more variety, while the personal sample was mostly made up of just a few species.

The limitations of this experiment include a small sample size, with only 21 data points (one for each student), which limits the generalizability of the results. Additionally, sampling bias may have influenced the findings, as the results depend on the specific areas of the keyboard each student swabbed, which might not represent the bacterial diversity across the entire keyboard. Furthermore, human error and/or contamination during the sampling or handling process could have impacted the accuracy of the results.

What This Means

The higher equitability in the Personal sample means the species were more balanced, while the Public sample had some species dominating over others. This fits with what we often see in nature—some places have a mix of different species, while others have just a few that take over.

Overall, these calculations help show the differences in species diversity between the two environments and give a better idea of how species are distributed.

The results of this experiment clearly demonstrate the differences in bacterial diversity between personal and community keyboards. While the community keyboard exhibited a higher variety of bacterial species, likely due to the greater number of users and the increased exposure to various environments, the personal keyboard showed a more limited bacterial profile. This suggests that shared surfaces, like community keyboards, may act as hotspots for microbial transmission, supporting the hypothesis that the variety of bacteria on a surface correlates with the number of individuals who interact with it. The findings underscore the importance of regular cleaning and hygiene practices, especially for communal devices, to prevent the spread of potentially harmful bacteria. Despite limitations such as sample size and potential contamination, the data provides valuable insight into the microbial landscapes of everyday objects, highlighting the role of human interaction in shaping bacterial environments.

Literature Cited

Eisenberg, J. (2020, March 18). Viruses live on doorknobs and phones and can get you sick-smart cleaning and good habits can help protect you - the pursuit - University of Michigan School of Public Health. Viruses Live on Doorknobs and Phones and Can Get You Sick- Smart Cleaning and Good Habits Can Help Protect You - The Pursuit - University of Michigan School of Public Health. https://sph.umich.edu/pursuit/2020posts/smart-cleaning-for-viruses.html

U.S. Department of Health and Human Services. (2015, August 31). NIH human microbiome project defines normal bacterial makeup of the body. National Institutes of Health. https://www.nih.gov/news-events/news-releases/nih-human-microbiome-project-defines-normal-bacterial-makeup-body