Full Length Research Paper

Comparison of the effects of UV-A radiation on Leptospira interrogan serovar Bataviae, Canicola and Pomona

Sudarat Chadsuthi¹, Jirasak Wong-ekkabut^1,2, Wannapong Triampo^1,3,6*,  Galayanee Doungchawee⁴ and Darapond Triampo^1,3,5,6

¹Group of Biological and Environmental Physics, Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.

²Department of Physics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand.

³Center of Excellence for Vectors and Vector-Borne Diseases, Faculty of Science, Mahidol University, Salaya Campus, Nakhon Pathom 73170, Thailand.

⁴Department of Pathobiology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.

⁵Department of Chemistry, Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University,  Bangkok 10400, Thailand.

⁶ThEP Center, CHE, 328 Si Ayutthaya Road, Bangkok 10400, Thailand.

*Corresponding author. E-mail: scwtr@mahidol.ac.th, wtriampo@gmail.com.

Tel: +662 441-9816 ext. 1131. Fax: +662 441-9322.

Abbreviations: SEM, Scanning electron microscopy; TEM, transmission electron microscopy; UV-A, ultraviolet-A; IR, infrared; UV-VIS, ultraviolet-visible; OD, optical density; DFM, dark field microscopy; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; PVDF, polyvinylidene fluoride; PBS, phosphate buffer saline; DAB, diaminobenzidine; HPR, horseradish peroxidase; OMP, outer membrane proteins; LPS, lipopolysaccharide.

Accepted 29 April, 2010

   Abstract

Motivated by the lack of related studies and an insufficient understanding of the response of pathogenic spirochetes, including leptospira to ultraviolet-A (UV-A) (or other stresses), we comparatively studied the effects of UV-A radiation on the Leptospira interrogans serovar Bataviae, Canicola and Pomona. The main purpose of this work was to investigate the effects of UV-A irradiation—both short term (immediate) and long term (post-irradiation)—on leptospires at different UV-A dosages, controlled by the duration of exposure time. It was observed that survival fractions linearly decrease from 100 to about 70, 60 and 50% for serovar Pomona, Bataviae and Canicola, respectively. This indicates that, for different serovars, UV-A irradiation has a quantitatively different effects on growth. Short term effects suggest that Pomona may be more resistant to UV-A than the other serovars. Long term effects show that, when compared with the control group, the treated groups of bacteria re-grow when the exposure time is equal or lesser than 6 h (~ 2 - 6), while the groups exposed for 12 h or longer experienced little change or a slight decrease. This may indicate that UV-A radiation is able to inhibit the growth of bacteria, but does not prevent self-defense from taking place. UV-A radiation’s effect on antigenic components was also investigated. The immunoblotting method was used and the results are supported by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results. Possible explanations for these results are discussed.

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