1. The Effect of Ultra Violet Light Exposure On The Growth of Antibiotic Resistant Bacteria Brad Kauffman, Department of Biology, York College Methods Introduction Ultraviolet light can be an effective bactericidal agent, due to its interference in DNA synthesis and repair UV light is absorbed by double bonds in pyrimidine bases and the energy released from bond breakage is used to form pyrimidine dimers (Washington et al. 2000). Bacteria have repair mechanisms but sometimes too many excisions are made and after too much exposure bacterial repair mechanisms cannot keep up with damage and the DNA becomes denatured and destroyed (Muhammed 1969). Certain wavelengths of energy are responsible for disrupting certain bonds such as the P-O, O- H, and N-H bonds which are important in the structure of DNA (Vermeulen et al. 2007). Lower wavelengths in the UV spectrum have enough energy to disrupt these bonds making them unstable which can cause the dimers which eventually leads to the bactericidal effects UV is light also effective at destroying bacteria that are antibiotic resistant as well as bacteria that can lay dormant by forming spores (Waites et al. 1988). UV light is becoming very popular as a step in sterilizing or sanitizing certain things such as surgical instrument tables, incoming air from vents leading into operating rooms and wastewater in sewage treatment plants (Fitzwater 1961) and (Meckes 1981). Objectives Isolate antibiotic and sensitive strains of different species of bacteria Expose antibiotic resistant bacteria to different time intervals of ultraviolet light, consisting of 30, 60, and 90 seconds Compare the average growth of bacterial colonies of the different time trials for each species of the antibiotic resistant strains Results Initial isolations found bacteria to be multi-resistant to chloramphenicol, erythromycin, and ampicillin. Bacterial growth was found on most 30 second time trials, although some seemed to revert back to sensitive because zones of inhibition were present. UV light exposure for 60 and 90 seconds had good bactericidal activity. Comparison of 60 and 90 second time within same species using un-paired t-test showed the means of colony growth to be significantly different Figure 1. Unpaired t-test comparing colony growth between 60 and 90 seconds of exposure to UV light Figure 2. Unpaired t-test comparing colony growth between 60 and 90 seconds of exposure to UV light Figure 3. Unpaired t-test comparing colony growth between 60 and 90 seconds of exposure to UV light Isolated pure colonies of mutant bacteria resistant to one antibiotic Re-tested mutant strains for resistance to other antibiotics. Also isolated sensitive strains of the same species for use as controls Took samples of each mutant and resistant species and spread on separate nutrient agar plate. Placed each mutant species in UV light hood for 30 seconds 10 different times. Placed antibiotic discs on agar after exposure on mutant strains. Followed same procedure for 60 and 90 seconds for each species. Performing 10 trials for each of the remaining species. Compared data of each species’ 60 and 90 second growth results to exposure to UV light. Conclusions Any exposure to UV light causes some bacteria mortality 30 seconds was not enough to stop lawn growth although it seemed to revert some of the mutants back to sensitive strains without fully killing everything The results of the unpaired t-tests show that there are significant differences in the number of bacteria able to grow with exposure to 60 and 90 seconds of UV light exposure The extra 30 seconds of exposure from 60 to 90 seconds made a big difference in bactericidal activity Literature Cited 1. Fitzwater, J. 1961. Bacteriological Effect of Ultraviolet Light on a Surgical Instrument Table. The American Journal of Nursing 61:71-75. 2. Meckes, Mark C. 1981. Effect of UV Light Disinfection on Antibiotic- Resistant Coliforms in Wastewater Effluents. Applied and Environmental Microbiology. 43:371-377 3. Muhammed, Amir, and Setlow, Jane K. 1969. Ultraviolet-Induced Decrease in Integration of Haemophilus influenzae Transforming Deoxyribonucleic Acid in Sensitive and Resistant Cells. American Society for Microbiology 104:44-48 4. Vermeulen, N., Keeler, Werden J., Nandakumar K., and Leung, K.T. 2007. The Bactericidal Effect of Ultraviolet and Visible Light on Escherichia coli. Biotechnology and Bioengineering. 5. Washington, M. Todd, Johnson, Robert E., Prakash, Louise, Prakish, Satya. 2000. Accuracy of thymine–thymine dimer bypass by Saccharomyces cerevisiae DNA polymerase η. Proceedings of the National Academy of Sciences. 97:3094-3099 6. Waites, W.M., Harding, S.E., Fowler, D.R., Jones, S.H., Shaw, D., and Martin, M. 1988. The destruction of spores of Bacillus subtilis by the combined effects of hydrogen peroxide and ultraviolet light. Letters in Applied Microbiology. 7:139-140 Acknowledgements I would like to thank Dr. Mathur for all her help in the idea and design of the experiment as well as her help throughout the entire process. Also put sensitive strains on agar plates along with antibiotic discs without subjecting to UV light. These were used as controls to make sure my mutants were still resistant at each trial.