ULTRAVIOLET EXPOSURE AND BACTERIAL GROWTH

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Ultraviolet Exposure and Bacterial Growth

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Ultraviolet Exposure and Bacterial Growth

Procedure

The researchers labeled the bottom of the plate with the name of the bacteria sample and the duration of exposure to UV radiation . The plate was then divided into two and labeled each part to distinguish the EXPOSED from the UNEXPOSED portion . Then , the bacteria samples were introduced into the agar surface of their respective plates by

using sterile cotton swab . The samples were then air-dried for five minutes and covered with the plate cover . Before the plates were irradiated , the cover was removed and replaced with an index card but only the part that was labeled UNEXPOSED ' After covering the part labeled UNEXPOSED (served as Control , the plates were then irradiated under UV lamp for 55 seconds . Then , the plate covers were replaced and wrapped with aluminum foil to prevent from exposure to white light . The plates were then incubated at 37 degrees for 48 hours . Finally , the bacterial growth of the EXPOSED portion of the plates were observed and compared with the bacterial growth in the UNEXPOSED part

Difficulty

One difficulty that the researchers might face is distributing the sample bacteria evenly along the agar surface . If the distribution is uneven , it might result to a wrong conclusion . Another is the presence of other bacteria in the plates . When the plates are exposed in open air , it might collect some unsolicited bacteria

Precautions

The researchers must take the following precautionary measures

Clean the plates before using them

Get a clean sterile cotton swab to avoid contamination

Never allow the UNEXPOSED part exposed to white and UV light

Always wear masks when working with the bacteria samples

Data and Observation

Table 1 . Comparison of Bacillus cereus and Serratia marcescenes growth with exposure and without exposure

Time (s ) Bacillus cereus Serratia marcescenes

Exposed Control Exposed Control

2 4 4 3 .5 4

5 4 4 3 .5 4

10 3 .5 4 2 .5 4

15 3 4 1 4

25 2 .5 4 0 4

35 2 4 0 .5 4

45 2 4 1 4

55 1 .5 4 0 .5 4

65 1 .5 4 0 .5 4

Average 2 .67 4 1 .44 4 Results showed that the growth of the bacteria exposed in UV light decreased as time increases while for the unexposed (CONTROL , the growth was continuous . Between the two bacteria , Bacillus cereus had higher tolerance for UV radiation as seen from its average growth (2 .67 while Serratia marcescenes are less tolerant (1 .44

Conclusion

Therefore , growth of bacteria is suppressed when exposed to UV radiation . Radiation interferes with the DNA functions , such as replication , and can result to death of cells

References

Mehta , R . and K . Hawxby . Use of untraviolet radiation to achieve bacteria-free algal culture . Retrieved Oct , 25 , 2007 , from HYPERLINK "http /digital .library .okstate .edu /oas /oas_htm_s...