This document summarizes a student's research project that sampled 12 surfaces in men's and women's bathroom daily over a week to quantify microbes present. The student plated samples on two types of media and counted colony forming units. The results showed the men's bathroom had more growth than women's, though not significantly. Tuesday had significantly more growth than Friday. The paper towel dispenser had the most growth of all surfaces sampled. Though some differences were found, the student notes limitations and that not all bacteria collected may be harmful.

1. Dampen a
sterile swab in
sterile water.
Step 1
Swab the area
of interest and
place the swab
back into the
tube. Do this
twice for all
surfaces of
interest.
Step 2
Plate the
samples. Each
surface will have
two plates, one of
each type of
media. Incubate
the plates for 24
hours at
37° C.
Step 3
Count colony
forming units
that developed
from each of
the samples.
Step 4
Bathroom Microbiota
Emelia Gwin | Northwest Missouri State University
Hypothesis
• I predict that the men’s bathroom will have more microbes
than the woman’s bathroom.
• I think that Monday’s samples will accumulate the most
microbial growth and Thursday's will be the least.
• I predict that the surface with the most microbes will be the
soap dispenser and the surface with the least microbes will
be the paper towel dispenser.
Project Overview
I sampled 12 surfaces in the men’s and women’s
bathrooms and plated the samples to quantify the microbes
present. This was done daily over the course of a week and
the samples were collected around the same time each day.
Two types of media was used to promote maximum colony
growth. All samples were considered in the results and
conclusions.
Background
Hypothesis 1: The
difference between
men’s and women’s
bathrooms.
• With 38,031 CFUs,
the men’s bathroom
had more microbial
growth than the
women’s, who
accumulated 31,245
CFUs.
Hypothesis 2: Days
of the week
• Tuesday had the
most microbial
growth with 19,203
CFUs and Friday
had the least with
only 5,659 CFUs.
Hypothesis 3:
Comparing the
surfaces sampled
• The paper towel
dispenser
accumulated the
most microbes with
40,279 CFUs while
the second door
coming into the
bathrooms had the
least with only 304
CFUs.
Materials
Materials Needed Quantity
Sterile swabs 120
Sterile water 100 mL
Tryptic Soy Agar 60
Plate Count Agar 60
Gloves 5 pairs
Procedure
Data / Observations
Results
Conclusions / Discussion
Although the data shows that the men did have more colony growth
than the women, the results proved to be statistically insignificant. The
differences were small and could have been by chance. There was a
much bigger difference between the colony growth on Tuesday’s and
Friday’s samples. This difference proved to be statistically significant and
there does seem to be a correlation between the day of the week and
how many microbes are present. It would have helped my project to
have had access to an electronic people counter as they did in Porzig-
Drummond et al to see what the difference in traffic flow would be
between these two days. Finally, it was proven to be significant that the
paper towel dispenser had the most colony growth among all other
surfaces sampled with the second door leading into the bathroom having
the least amount of colony growth. This does not conclude that the paper
towel dispenser is the dirtiest surface in the bathroom. Some bacteria are
natural and not harmful. Since I did not sequence the samples, I cannot
tell whether the bacteria collected were good or bad bacteria.
Works Cited
Davies P. 1982. Please wash your hands. Archives of Disease in Childhood 57:647-648.
Erasmus V, Brouwer W, vanBeek EF, Oenema A, Daha TJ, Richardus JH, Vos MC, and Brug J. 2009. A qualitative exploration of reasons for poor hand
hygiene among hospital workers: lack of positive role models and of convincing evidence that hand hygiene prevents cross-infection. Infection Control
and Hospital Epidemiology 30(5): 415-419.
Fattorini M, Ceriale E, Nante N, Lenzi D, Manzi P, Basagni C, and Messina G. 2016. Use of a fluorescent marker for assessing hospital bathroom
cleanliness. American Journal of Infection Control 4: 1066-1068.
Fierer N, Hamady M, Lauber CL, and Knight R. 2008. The influence of sex, handedness, and washing on the diversity of hand surface bacteria. PNAS
105(46):17994-17999.
Porzig-Drummond R, Stevenson R, Case T, and Oaten M. 2009. Can the emotion of disgust be harnessed to promote hand hygiene? Experimental
and field-based tests. Social Science & Medicine 68: 1006–1012.
16799
19203
17056
10559
5659
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
MONDAY
TUESDAY
WEDNESDAY
THRUSDAY
FIRDAY
Colony Forming Units (CFUs)
DayoftheWeek
Bacterial Growth vs Day of the Week
2213 3181
304 537 324 501
3126
1268 625
16327
591
40279
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
ColonyFormingUnits(CFUs)
Surfaces Sampled
Colonies Collected on the Surfaces Sampled
Cleanliness is important in preventing the spread of
disease among individuals. Several different types of
experiments have been conducted to calculate hand hygiene
and cleanliness. Davies claims that the skin under and around
the nails are where the most bacteria sits on a person’s
hands. This is why 11 out of the 12 surfaces I chose to sample
are surfaces you would often touch with your hands. In
Fatterini et al, they used plate count agar and assessed the
colony forming units per plate to determine cleanliness of
bathrooms found in hospitals. A florescent marker was also
used to mark various surfaces in the bathrooms which was
later evaluated to see if the marks remained after two
cleanings. Fierer et al looked at the differences between male
and female microbial biota. They sampled the palm surface of
people and noted their handedness. They found that there
was a difference not only between man and women but also
between dominant and non-dominant hands of the same
individuals.
Instead of using qualitative data as they did in Erasmus et
al, I chose to take a more quantitative approach by counting
colony forming units per plate. Using the information I
obtained through researching studies similar to what I was
interested in, I compiled my own research project. My
background knowledge in microbiology also helped me in
choosing the right materials and procedures to take in order to
obtain the best results.