Streptococcus pneumoniae Cell-Wall-Localized Phosphoenolpyruvate Protein Phosphotransferase Can Function as an Adhesin: Identification of Its Host Target Molecules and Evaluation of Its Potential as a Vaccine
Fig 2
PtsA mediates S. pneumoniae adhesion to target host cells.
A–E. A549 cells were grown to confluence and then blocked with 0,5% gelatin for 1 h. Excess gelatin was removed, and the A549 cells were incubated for 1 h with rPtsA at the denoted concentrations. Excess protein was then removed. S. pneumoniae was added for 1 h to the cells, non-adherent bacteria were removed, and cells were detached with trypsin and plated onto blood agar plates for counting. rPtsA inhibited the adhesion to A549 cells of: A) strain WU2 (p < 0.0001; r = −0.943), B) strain 3.8DW (p < 0.0001; r = −0.371), C) strain D39 (p < 0.0001; r = −1), and D) strain R6 (p < 0.0006; r = −1). E) rKLH, a protein used as a negative control, did not inhibit D39 adhesion to A549 cells (p = 0.8; r = −0.2). F–J. S. pneumoniae cells (WU2 and 3.8DW) were treated for 1 h with rabbit anti-rPtsA antiserum and added to gelatin-blocked A549 cells for 1 h; non-adherent bacteria were removed; and cells were detached with trypsin and plated onto blood agar plates for counting. Rabbit anti-rPtsA inhibited adhesion to A549 cells of: F) strain WU2 (p < 0.0001; r = −0.359); G) strain 3.8DW (p < 0.0001; r = −0.886); H) strain D39 (p < 0.0001; r = −0.943); and I) strain R6 (p < 0.0001, r = −0.406); J) Serum obtained from a rabbit prior to immunization did not inhibit the adhesion of strain WU2 to A549 (J p>0.005; r = +0.667). (p > 0.005; r = +0.667). Experiments were performed in triplicate and repeated at least 3 times. Values are means±SD. *Student's t-test p<0.05.