Comparative study of pili expression in Streptococcus agalactiae

Streptococcus agalactiae, or GBS, is an important opportunistic pathogen which causes pneumonia, sepsis and meningitis in neonates and severe diseases in immunocompromised adults. We have performed comparative genomics of prevalent GBS serotypes of Indian origin i.e., Ia, III, V and VII. Pili proteins were commonly found upregulated and their expression was studied by using antiserum for GBS80 (backbone protein of pilus island–I (PI1), GBS67 (ancillary protein of PI-2a) and SAN1518 (backbone protein of PI2b) by whole cell and Western blot analysis. To check the role of pili proteins in adherence and invasion, inhibition assay was performed. Comparative immunoblotting experiments revealed that pili proteins expression does not differ in geographically different selected serotypes, Ia and V of India and USA. In case of A549 we found that GBS VII invasion and adherence was inhibited by pili protein specific antiserum SAN1518 significantly (P=<0.001) by 88.5 and 91 % respectively. We found that mutant strains, deficient in the pilus proteins (Δgbs80, and Δsan1518 exhibit a significant decrease in adherence in case of type Ia, III, VII. We have found 95 % reduction in invasion when ∆SAN1518 was used in case of A549 cells. As the pili proteins were identified previously as vaccine candidates against GBS serotypes of developed countries and we also found their role in the attachment and invasion of GBS of Indian origin thus in turn present work supports the idea of making a more effective pili protein based vaccine which can be used universally.