The Effect of Antioxidants and pH on Photooxidative Stress with Methylene Blue of E. coli, S. aureus and C. albicans

Abstract

In this study, the effect of photooxidative stress on different microorganism groups (Gram positive, Gram negative and Eukaryote) and the role of pH and antioxidants on this effect were investigated. The study was performed under 3 day light fluorescent lamps (total 4950 lux) in phosphate buffer (5.0, 6.0, 7.0, and 8.0) at different pH values. As a result, the colony counts of Escherichia coli, Sthapylococcus aureus and Candida albicans were not decreased under photooxidative stress according to the starting number at pH 5.0 and 6.0. While E. coli and S. aureus at pH 8.0 were decreased 3 log and 3.38 log, it were decreased 1.27 and 1.56 log at pH 7.0. Similarly, C. albicans decreased 0.35 log at pH 7.0 and 0.75 log at pH 8.0. T99 value at pH 8.0 was determined as 4.0 hours for E. coli, 3.5 hours for S. aureus, and 15.7 hours for C. albicans (p < 0.05). When the effects of NaCl, Mannitol and ascorbic acid on photooxidative stressed microorganisms were examined, it was determined that NaCl protected microorganisms against photooxidative stress, and ascorbic acid and mannitol changed their effect according to microorganism. In conclusion, photooxidative stress were found to be more effective to Gram positive than Gram negative bacteria, more effective to bacteria than eukaryotes. The effectiveness of photooxidative stress has been determined to be quite high at alkaline pH. It was also determined that there is a direct relationship between the effect of photooxidative stress and pH and osmolarity. It has been found that Ascorbic acid and Mannitol are not protective against photooxidative stress in Gram-positive and eukaryotic cell. Yet the cause of this condition is unknown.