Growth Kinetics and Protein Expressions in Biofilms of Streptococcus Agalactiae Isolated from Bovine Mastitis Cases

Biofilm formation is a survival strategy of bacteria produced when nutrients are in minimal concentration along with an inert surface. In the present study, different concentrations of Luria-Bertani (LB) broth, namely 0.625, 1.25 and 2.5 per cent; tryptone soya broth (TSB), namely 0.32 per cent, 0.75 per cent, 1.5 per cent and 3 per cent as growth media and bentonite clay as inert surface were tried to obtain maximum biofilm formation by Streptococcus agalactiae (SA). As a result, maximum biofilm cells were obtained on day three post-inoculation for 0.625 per cent LB glucose with 0.3 per cent bentonite clay, whereas planktonic cells showed maximum growth on day one post-inoculation in 2.5 per cent LB glucose medium. The TSB with bentonite clay was not suitable for biofilm formation by this organism. The decline of biofilm cell population was very gradual and survived at very high counts even after 10 days of post-inoculation, whereas planktonic cells underwent rapid autolysis indicating that biofilm cells survived for longer periods compared with planktonic cells in adverse conditions and could interface with body defence and generally used antibiotics. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis of proteins extracted from SA biofilms and free cells revealed marked difference. In biofilms, several proteins were over expressed; in contrast, these proteins were very less or not expressed in free cells. As a result, the comparison between biofilm and free cells provides valuable information on protein expression profile of SA biofilm and free cells.