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

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.