We studied the bindings of human influenza A type viruses to group B Streptococcus (GBS), types Ia, II, III and IV, of sialic acid (SA)alpha2-3 linkage, using A/PR/8/34(H1N1) and A/Memphis/1/71(H3N2). The viruses were found to bind to all types of GBS, with the exception of PR/8/34 for GBSII, and to elute from GBSIa, III and IV at 37 degrees C, except GBSII. Electron microscopy confirmed these behaviours of the influenza viruses. The virus-binding capability of GBS types seemed to depend on the side chain length of the terminal SA. Treatment of GBSIa, III and IV, except enzyme-resistant type II, with bacterial neuraminidase resulted in the loss of virus-binding capability of GBS. These findings confirmed that SAalpha2-3 linkage of GBS capsules functions as receptor for human influenza viruses. When singular bacteria were prepared from mainly chain-like GBS with sonication, viruses were found to bind to them more efficiently. Untreated and sonicated GBS were both aggregated with high doses of virus. Furthermore, using A/Memphis/1/71(H3N2) and GBSII, we found that virus-bound GBS, untreated or sonicated, caused haemagglutination (HA). The morphological evidence that chicken erythrocytes were bridged with virus-bound native GBSII, supporting occurrences of HA, was obtained. Statistical analysis suggested that HA by virus-bound sonicated (singular) GBS was mediated by bacteria bound by at least two or three virus particles.

Using the virus-binding assay and scanning electron microscopy (SEM), influenza A and B type viruses and two paramyxoviruses, parainfluenza (Sendai) and mumps viruses, were found to bind to Group B Streptococcus (GBS), type Ia and II, with the terminal sialyl-galactose linkage, although some viruses detached during the sample processing for SEM, and mumps virus did not bind to GBSIa. Binding of viruses eluted from GBS at 37 degrees C depended on combination of virus and GBS. The biological significance of these findings is discussed.