Bacterial Growth Lab

Results

Part 1: Effects of Heat on Bacterial Growth

Table 1. Bacterial Growth Based on Heat 40°C

(Group 1) 55°C

(Group 2) 80°C

(Group 3) 100°C

(Group 4) and (Group 5)

Time (min) 10 20 30 40 10 20 30 20 30 40 10 20 30 40

Escherichia coli X X X O X X X O O O OO OO OO O

Bacillus subtilis X X X O X X X X X X OX XX OX X

X = growth; O = no growth

Results for Group 2: 550 C for up to 30 minutes did not produce a thermal death time (TDT) or thermal death point (TDP) for either E. coli or B. subtilis. Since there were only 3 team members, the 40 minutes at 550 C results were not available.

Looking at the chart as a whole, for E.coli, 40 minutes at 550 C could be the thermal death time and 550 at 40 minutes could be the thermal death point as there

This seems to be highly accepted, however it is not indicative of the results that Group 2 obtained. Group 2 used E. coli as the bacteria sample for the UV exposure portion of the experiment. There was no reduction in the bacterial growth on the side where UV light was used as compared to the side that was kept from the UV light. These results, or lack of results, were unexpected and when compared to other groups in lab, appeared to be inaccurate. It appears that Group 2 's UV light did not work. Group 3 allowed Group 2 to use their results for comparison as they were deemed accurate when reviewed by the lab

In the lab, the effects of colder temperatures were observed. As the temperatures decreased, the growth of the two microorganisms being observed, B. subtilis ans S. marcescens, slowed and eventually stopped. Both bacteria were susceptible to the coldest temperature observed. This was the expected result and one that is probably applicable to most microorganisms when dealing with very high or very low temperatures. However, there are microorganisms known as pscyrophiles, which prefer extremely cold temperatures and hypothermophiles which prefer extremely hot