Prokaryotic Growth Rate


Bryan Tomsula, Eric Westerlind, April Zietz


CU Boulder, Fall 2007


The purpose of this study is to test the bacterial growth rate of various places in everyday life using bacteria cultures in agarose gel.  Bacteria are mainly unicellular prokaryotic organisms that are ubiquitous to every habitat on Earth.  They grow through cell division and under optimum conditions some are known to be able to double their population in less than ten minutes.  Using Petri dishes containing agarose gel a pure sample of the bacteria in a certain location can be isolated and cultured to determine which location would have the highest growth of bacteria.


In order to gather a sampling of the bacteria on a specific location a sterile swab was used to gather a representative culture of the bacteria in the area.  Two swabs of each location will be taken so as to minimize the chance of a single outlier example skewing the results.  The sterile swab turned out to be a band-aide and in order to make sure it was sterile a control with a sterile swab will be measured.  To measure the growth rate the percent coverage of the agarose plate will be measured and then compared to the other locations to determine the fastest growth rate.  Measurements were made twice daily during a three day test period under controlled conditions to minimize the amount of contamination.  It was hypothesized that the toilet sample will have the highest percent coverage after the three day test period.


The results did show the highest single Petri dish sample was the second toilet sample with a 33.5% coverage, followed by the second SCARPY computer station sample (33%) then the second bus sample (30%).  The difference in the percent coverage in the toilet sample with the SCARPY and bus samples was significant with P-values of 0.0002 and 0.0034 respectively.  Although with other samples (atm 1&2, stairs 1, and bus 1) there was no significance, suggesting that these values could be higher than the toilets, but will be unsure to prove without further tests.


These results are semi-consistent with the initial hypothesis in that the culture with the highest percent coverage was one of the two toilet cultures.  In order to be positive that these results are accurate within the 95% confidence level, all p-values would need to be less than 0.05, but since some were greater it can not be concluded that the toilet was the highest.  The hypothesis does not need to be modified because with further testing it can be proved that either the toilet is significant and has the highest growth rate or is significant and does not have the highest growth rate.  Also with more testing all possible contamination can be eliminated by the elimination of outliers that could possibly arise from a faulty swab or contamination of the swab during the gathering of the culture.


Further study will need to be done with more locations and swabs per location to determine where the location with the most bacteria is.  Also experiments as to the different reactivity of the bacteria with various antibiotic soaps would be interesting.