Comparative Proteomic Analysis of Leptospira Interrogans Serogroup Icterohaemorrhagiae Human Vaccine Strain and Epidemic Isolate of China

Background: Leptospira interrogans serogroup Icterohaemorrhagiae is the predominant pathogen causing leptospirosis in China and is still used as the vaccine strain for the current human inactivated vaccine. Unlike the clade ST17, which is distributed worldwide, ST1 is the most prevalent in serogroup Icterohaemorrhagiae in China. Purpose and Methods: To further characterize leptospiral pathogens, isobaric tags for relative and absolute quantitation and parallel reaction monitoring were used to analyze differences at the proteomic level between serogroup Icterohaemorrhagiae vaccine strain 56001 (ST1) and circulating isolate 200502 (ST17) from different periods. Results: Two hundred and eighty-one proteins were differentially expressed between ST17 and ST1, of which 166 were upregulated (>1.2 fold change, P < 0.05) and 115 (>1.2-fold change, P < 0.05) were downregulated. Function prediction revealed that nine upregulated proteins were outer membrane proteins, including several known immunogenic and/or virulence-related proteins, such as ompL1, LipL71 and LipL41. Furthermore, important expression differences in carbohydrate, amino acid, and energy metabolism and transport proteins were identified between ST1 and ST17, suggesting that these differences may reflect metabolic diversity and the potential of the pathogens to adapt to different environments. Conclusion: In summary, our findings provide insights into better understanding the component strains of the Chinese human leptospirosis vaccine at the proteomic level. Additionally, these data facilitate evaluating the mechanisms by which pathogenic Leptospira species adapt to the host environment.