Abstract

The effect of exposure to ultaviolet-A (UVA) radiation was studied on the pathogenic spirochetes Leptospira interrogans serovar Canicola for different time durations. Changes in cell growth and viability due to UVA exposure were determined by using the conventional microscopic agglutination test (MAT), dark-field microscopy and spectrophotometry measurements. Changes in antigens and protein expression in the cells were detected by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot. Decrease in cell growth and viability was found to be related to the exposure period, or was dose dependent. The growth decreased sharply at a very high rate for the first 24 h of exposure (112.3 J/cm²); then it reached the minimum within about a 1d of exposure and leveled off for further treatment until the 7d exposure period. Immunoblot revealed the presence of 21 kDa antigenic protein in the unexposed cells, which disappeared after exposure to UVA for 24 h. SDS-PAGE analysis indicated the presence of a 76 kDa protein band in the cells exposed to UVA for 2 to 24 h. Exposure to UVA for more than 24 h decreased this protein, but the proteins of molecular mass between 56 and 70 kDa appeared. This work is the first step toward understanding the effects of UVA on leptospira bacteria. Further investigation of the mechanisms involved in UVAinteraction with leptospira will eventually lead to development of new strategies to control or prevent leptospira in the environment.

Key words: Ultraviolet-A, pathogenic spirochete, leptospirosis, Leptospira interrogans.