Some people report that according to observations in the United States, the infection rate of group B streptococci is increasing, and the reason is still unclear. In recent years, there have been many reports of neonatal infections caused by this group of bacteria, which has attracted people's attention. According to the difference in surface antigens, it can be divided into nine subtypes, namely Ⅰa, Ⅰb, Ⅱ, Ⅲ, Ⅳ, Ⅴ, Ⅵ, Ⅶ and Ⅷ. It can show type A, type B or type C hemolytic reaction on the blood plate. The streptolysin produced by the hemolytic strain is different from O and S of group A bacteria and has no antigenicity. According to the biochemical classification method, this group of bacteria is Streptococcus agalactiae (S. agalactiae).