Growth of viridans streptococci on human serum alpha(1)-acid glycoprotein

Viridans streptococci have emerged as major opportunistic pathogens. We sug gest that for these bacteria to proliferate in vivo and cause disease, they must utilize host tissue components. We have therefore examined he ability of all recognized species of viridans streptococci to liberate and utilize the constituent sugars of the glycans of the extensively sialylated human serum alpha(1)-acid glycoprotein (AGP) as the sole source of carbohydrate t o support in vitro growth. Analysis of residual glycans following bacterial growth was performed by high-pH anion exchange chromatography with pulsed amperometric detection and matrix-assisted laser desorption ionization time -of-flight mass spectrometry. Only those species which produced sialidase-n amely, Streptococcus oralis, S. intermedius, and S. defectivus-grew on AGP. The extent of degradation of glycans was dependent on the particular glyco sidases produced by the bacteria. S. defectivus produced only a sialidase w hich released the terminal N-acetylneuraminic acid residues of the glycans, and the Liberated sugar was utilized. S. intermedius also produced beta-ga lactosidase and beta-N-acetylglucosaminidase, which removed galactose and N -acetylglucosamine from desialylated glycans, all of which again were utili zed by the organism. S, oralis produced beta-galactosidase, beta-N-acetylgl ucosaminidase, and alpha-fucosidase and novel alpha- and beta-mannosidases which were apparent only from the analysis of the residual sugars of AGP. S . oralis cleaved all the sugars from AGP except for 22% of the N-acetylgluc osamine. The residual N-acetylglucosamine residues remaining were those lin ked to the asparagine of the peptide backbone. All the monosaccharides rele ased by S. oralis from AGP, with the exception of fucose, were utilized. Si alidase production may be a key factor for growth of these species of virid ans streptococci on glycoproteins in vivo, since they are commonly associat ed with extra-oral diseases, with S. oralis emerging as an important pathog en.