Killing bacteria
Temperature vs. BacteriaAlan Wu, Robert Lee, Jason Woo &
Janita ZhangRESEARCH QUESTIONAT WHAT TEMPERATURE WILL THE BACTERIA
FROM POND WATER BE KILLED?Independent VariableTemperature (Hot
Water Bath)Dependent VariableAmount of bacteria, presence of
coliform bacteria
Controlled VariableAmount of water (20mL)Amount of time heated
(2min)Incubator Temperature (35/40 degrees Celsius)Amount of water
used for coliform test (1mL)HYPOTHESISAs temperatures increase the
amount of bacteria decreases thus by boiling point (100C) all
bacteria that are harmful to humans will be killed.
1
Procedure Prior to Main ExperimentCollect sample of pond water
and cultivate bacteriaProcedure Main Experiment
Place test tubes of distilled water in hot water bathAdjust to
desired temperature (lowest to highest temperature)Temperature
reached add bacteria from agar plates into the test tube, leave in
for 2min.Agar Plates & Coliform Test
Reason for using coliform bacteria as an indicator is because it
is usually from a similar source as pathogens (i.e. fecal
contamination usually contains both coliform bacteria and
pathogens). Coliform is easier to identify, and finding pathogens
in a sample is often troublesome, unfeasible, and may even be
hazardous. So coliform testing is a reasonable indication for
whether pathogens exist or not. Total coliform bacteria count is
often used as a primary indicator for water contamination.3
Raw Data
Agar plates showed inconsistent results because they all showed
growth of bacteria. However, the coliform tube tests showed a
gradual colour change from lower temperatures to higher
temperatures, the liquid in the lower temperatures changed to a
yellow/greenish colour and the higher temperatures maintained the
purple colour displaying that coliform bacteria does not exist.
Since the presence of coliform bacteria is a good indicator of
pathogens (bacteria that is harmful to humans), the bacteria
present in the agar plates of higher temperatures is possibly
bacteria that is not harmful to humans. Since the agar plates did
not narrow down to cultivating a specific bacteria, all kinds of
bacteria, whether harmful or not to humans, could grow on the agar
plates thus the agar plates support that not all bacteria can be
killed at high temperatures, however, according to the Wilderness
Medical Society, water temperatures above 70 C kill all pathogens
within 30 minutes and above 85 C within a few minutes. So in the
time it takes for the water to reach the boiling point (100 C) from
70 C, all pathogens will be killed. Of the majority of the coliform
results, this can be supported. The first test tube that stays
purple lands on the test tube of 70 C. Comparing the results from
40 C-65 C and 70 C-100 C it is significant that coliform bacteria
is certainly present in the lower temperatures and not present in
the majority of the higher temperatures. 4
Analysis
< 65C65C
