Effect of chelating agents on the growth, surface polypeptide synthesis and interaction of Streptococcus agalactiae with human epithelial cells

In the present study, the influence of the chelating agents of ethylenediaminetetraacetic acid (EDTA), ethylene glycol-bis (β-aminoethyl ether) (EGTA) and 1,10-phenanthroline (PHEN) on growth rate, cytoadherence ability and surface protein expression was examined in a clinical strain of Streptococcus agalactiae isolated from a blood sample. EDTA and EGTA at 10 mM did not inhibit the growth of S. agalactiae, while PHEN significantly arrested bacterial proliferation in a concentration range of 10-0.01 mM. The in vitro interaction between S. agalactiae and A549 cells was a time-dependent process; adherence and bacterial intracellular viability were more pronounced after 3 h of contact. The pre-treatment of bacterial cells with EDTA adversely influenced the adhesive properties of S. agalactiae to A549 cells after 2 and 3 h, whereas EGTA only blocked this process after 3 h. Viable intracellular bacteria were just detected after 3 h of interaction, and EDTA and EGTA inhibited intracellular viability in a similar fashion. Conversely, PHEN inhibited neither the adherence nor the intracellular viability of the microorganism. Furthermore, EDTA robustly suppressed surface polypeptide synthesis, suggesting a decline in the possible bacterial ligands responsible for S. agalactiae adhesive properties.