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Bacterial Growth on Public Restroom Toilet
Seats vs. Bacterial Growth on Public Restroom
Door Handles: A Microbiological Approach
Jamie J. Larsen
Undergraduate Student (Biology Concentration)
Department of Biology
Tennessee Technological University
Cookeville, TN 38505
Introduction
 People have come to desire information that
would tell them how to disinfect particular
areas (Ojima et al 2002).
 No one has yet used uniform sampling
conditions to derive bacterial count
distributions (Ojima et al 2002).
Introduction (cont’d)
 The accumulation of this data would lead to
research that could contribute to the
estimation of infection risks for
communicable diseases (Ojima et al 2002).
 Flushing of a toilet produces bacteria-laden
aerosols which settle on the toilet and
bathroom surfaces (Rusin et al 1998).
Introduction (cont’d)
 Bathroom sites such as the toilet bowl surface,
flush handle, and floor are often contaminated with
E. coli and other coliforms due to direct
transmission from flushing of the toilet (Rusin et al
1998).
 Many enteric pathogens are spread by the fecaloral route and it has been suggested that the
fallout of droplets containing fecal material, after
flushing the toilet, is an important infection hazard
within the bathroom (Barker and Jones 2005).
Introduction (cont’d)
 Another infection hazard in bathrooms is the
decreased number of people who wash their
hands.
 Handwashing is one of the most important
factors in controlling the spread of bacteria
and in preventing development of infections
(Guinan et al 1997).
Introduction (cont’d)
 Viruses can also be transferred due to
contact with public restroom surfaces.
 Viruses can survive on inanimate objects,
but their transfer and survival on hands also
plays a part in their transmission (Bellamy et
al 1998)
Introduction
 With the data obtained from studies on
bacterial growth on public restroom surfaces
it would be possible to promote the general
publics’ understanding of sanitation issues
and facilitate the provision of useful
information and products (Ojima et al 2002).
Objective/Hypothesis
 Objective
– Determine which surface contained the most
bacterial growth
 Hypothesis
– Public restroom toilet seats will contain the most
bacteria
 Null Hypothesis
– Both the toilet seats and the door handles will
contain the same amount of bacteria
Methods and Materials
 Materials (Goss 2006)
– Data Form
– 10 agar plates (divided in half)
– Sterilized cotton swabs
– Gloves
– Distilled Water
– Permanent Marker (to label plates)
– Incubator
Methods and Materials (cont’d)
 Methods (Goss 2006)
– Swabbed toilet seats and door handles in ten public
restroom sites
– Cleaned one site with bathroom cleaner
– Labeled/Streaked the agar plates
– Incubated for 48 hours
– Checked growth, did colony counts, and analyzed
results using the t-test statistic
(http://iweb.tntech/cabrown/Ecology%20labs/t-tests.doc)
– Repeated experiment
Results
 Even though two runs of the experiment
were conducted, each produced similar
results so therefore only data obtained from
the first experiment was used in
interpretation of the results.
 Sample size=9 not 10 due to too much
growth on one of the plates.
Results (cont’d)
Table 1: Bacterial Growth Colony Counts (Run 1)
Colony Counts
Colony Counts
Sample #
Toilet Seats
Door Handles
1
0
6
2
52
11
3
84
13
4
100
14
5
0
15
6
50
2
7
0
12
8
10
35
9
100
19
TOTAL
396
127
Results (cont’d)
Table 2: T-test Results
Toilet Seats
Door Handles
44
14.1
1867
86.11
Sample Size (n)
9
9
T-test Statistic
= 2.13 (2.13>2.10, reject null)
Mean (X)
2
Variance (s )
Results (cont’d)
Bacterial Growth Colony Counts:
Toilet Seats vs. Door Handles
Colony Counts
120
100
80
Toilet Seats
Door Handles
60
40
20
0
1
2
3
4
5
6
7
8
9
Sample Number
Figure 1: Bacterial Growth Colony Counts: Toilet Seats vs. Door Handles
Results (cont’d)
Figure 2: Picture of bacterial growth from one of the sites tested
Results (cont’d)
Figure 3: Bacterial growth at another site…
Results (cont’d)
Figure 4: Bacterial growth at another site…
Discussion
 Since it was found that public restroom toilet
seats contained the most bacterial growth, it
seems that bacteria-laden aerosols do tend
to settle more on the toilet seats rather than
on the door handles. (t-test=2.13>2.10,
Table 2)
 This then contributes to higher bacterial
growth colony counts.
Discussion (cont’d)
 Barker and Jones (2005) found that both the
bacteria attached to the sidewalls and those
present in the bowl water contribute to the aerosol
formation.
 This then exemplifies the amount of bacteria-laden
aerosols that settle on the surface of the toilet seat
and therefore it can be easily seen why it was
found that there is more bacterial growth on public
restroom toilet seats.
Discussion (cont’d)
 Another study done by Stuart and Jones (2006), in
which they sampled steel push plate door handles
at a University, found that while staphylococci
could be isolated from some of the restroom push
plates, the total numbers were very low and
included no isolates of S. aureus.
 This shows that even though the bathrooms tested
were found in an area where people regularly use
them throughout the day the researchers were
unable to isolate any bacteria from them.
Discussion
 A study done by Bellamy (et al 1998) found that
hemoglobin, indicating the presence of blood and
therefore possible contamination of surfaces with
blood-borne viruses, was found on toilet bowls and
toilet seats.
 Bellamy (et al 1998) also goes on to say that these
surfaces are frequently handled and could
therefore play a part in viral transmission.
Discussion (cont’d)
 This study agrees with the results of my
study in that contact with a public restroom
surface that is not thoroughly disinfected
could lead to transmission of bacterial and
viral infections.
Discussion (cont’d)
 The results of my research, however,
disagree with the results of Rusin (1998) in
which it was determined that the toilet seat
was the cleanest site tested.
 However, Rusin (1998) goes on to say that
this may be due to regular disinfection of the
toilet and therefore results in lower levels of
bacterial growth.
Discussion (cont’d)
 Another study that disagrees with my findings is a
study done by Ojima (et al 2002) in which they
found that coliforms and E. coli were not found on
toilet bowl rims and that the contamination level for
toilets was the lowest of the study.
 Ojima (et al 2002) goes on to say that this could
also be due to regular disinfection at the sites
tested.
Conclusions
 Reject null hypothesis
– T-test=2.13>2.10 (Table 2)
 Accept hypothesis
 There is more bacterial growth on public restroom
toilet seats than on public restroom door handles.
 Bacteria-laden aerosols do contribute to the
increased amount of bacteria found on the toilet
seats.
Conclusions
 Bacteria-laden aerosols tend to settle more
on the toilet seat rather than on the restroom
door handles.
 I hope that more studies can be done on the
amount of bacterial growth on environmental
surfaces.
Conclusions
 I think a good area of research would be on, not
only the amount of bacteria found on public
restroom surfaces, but also the types of bacteria
found on public restroom surfaces.
 I would also recommend research to be done on
exactly what types of bacteria found on public
restroom surfaces are problematic.
Conclusions
 I hope that the results of this experiment
help to educate the public about the amount
of bacteria found in public restrooms.
 I believe that by knowing this information,
people will become better aware of their
surroundings and improve their personal
hygiene in public restrooms.
??Any Questions??