The possibility of using vaccine to control bovine subclinical mastitis and human neonatal infection caused by group B streptococci

Abstract

Based on the phenotypic expression, group B streptococci (GBS) can be devided into two distinct biovars, the bovine and the human biovar. GBS of bovine mostly grow as sediment with clear supernatant in fluid media, form compact colonies in soft-agar, fail to ferment lactose and have hydrophobic surface character. In contrast, the human GBS grow mostly turbid in fluid media, showed diffuse colonies in soft-agar, ferment lactose and have a hydrophylic surface character. The result of the recent researchs showed that these phenotypic differences were not directly associated with the biovar but seemed to be more with the occurrence of polysaccharide capsules. Most of GBS of bovine expressed the protein surface character but not the polysaccharide capsule. This was confirmed with salt aggregation and hexadecane tests. In the pathogenesis of subclinical mastitis, the adhesion process is very important as the initiation step of bacterial colonization on the mammary cell surface. The occurence of haemagglutinin among GBS of bovine is very high. The haemagglutinin and hydrophobic proteins are believed as adhesins in mediating the adherence of this bacteria. The absence of capsule in most of GBS of bovine lead to be phagocytosed easily by the polymorphonuclear (PMN), so that there is a balance condition (homeostatic) between the amount of bacteria and the bacterial elimination by PMN in udder. This might be the explanation about the phatogenesis of the subclinical mastitis. The antiserum against haemagglutinin inhibits the adhesion of this bacteria on the mammary cell surface. The new approach in controlling mastitis by using vaccine should be considered and the vaccine candidates should be selected based on the occurrence of haemagglutinin on the surface of bacterial cells.