Teichoic acids of Streptococcus agalactiae: chemistry, cytotoxicity, and effect on bacterial adherence to human cells in tissue culture

Abstract

The ratio of teichoic acid to lipoteichoic acid (LTA) in a strain of Streptococcus agalactiae type III was found to be 8:1, with the total amount of LTA being 0.1% of the dry weight of the organism. Purified teichoic acid contained D-alanine and possibly a small amount of D-glucose and was approximately 22 glycerol phosphate units in length. The linkage between each of these units was 1-3. In addition, LTA contained a complex lipid, more glucose, and an unusually high content of a short-chain fatty acid, tridecanoic acid. This LTA was cytotoxic for a variety of human cell monolayers in tissue culture, including one derived from the human central nervous system. Established human cells were more sensitive than primary cell monolayers to this LTA, with as little as 12.5 micrograms of LTA per ml being cytotoxic for HeLa cells. Teichoic acid (250 micrograms/ml) was nontoxic under identical conditions. These cytotoxicity results suggest an LTA involvement in group B streptococcal pathogenesis. Also, the first model system for the study of group B streptococcal adherence to primary human embryonic amnion cells in tissue culture is detailed. This system was used to quantitate pronounced differences in tissue tropism between S. agalactiae and Streptococcus pyogenes and showed enhanced binding by this group A coccus over that of S. agalactiae for amnion cell monolayers. The adherence of both streptococcal species to only a portion (40%) of these amnion cells suggested that host cell receptor expression may vary for primary cells in vitro. Finally, this strain of S. agalactiae was shown to adhere to amnion cells by a non-LTA-mediated mechanism. The possibility of an LTA-mediated versus a protein-mediated adherence mechanism for host cells that is related to the virulence of S. agalactiae is discussed.