Human and bovine group B streptococci: two distinct populations

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Comparative Genomics

Background:

• Group B Streptococcus (Streptococcus agalactiae) is a significant human and animal pathogen.
• Understanding population structures is crucial for controlling disease transmission and developing targeted interventions.

Purpose of the Study:

• To compare cultural, biochemical, serological, and bacteriocin sensitivity properties of Streptococcus agalactiae from humans and animals.
• To determine if human and bovine isolates represent distinct populations.

Main Methods:

• Isolates were characterized using standard microbiological techniques.
• Tests included hippurate hydrolysis, CAMP test, bacitracin sensitivity, pigment production, hemolysis, carbohydrate utilization (salicin, lactose), serotyping, and bacteriocin sensitivity profiling.

Main Results:

• All isolates possessed the Group B carbohydrate antigen, were hippurate positive, and CAMP test positive.
• Human isolates were typically bacitracin resistant, pigment producing, hemolytic, and utilized salicin but not lactose.
• Bovine isolates were usually bacitracin sensitive, non-pigment producing, non-hemolytic, and utilized both salicin and lactose. Human isolates showed diverse serotypes and uniform bacteriocin sensitivity, while bovine isolates had varying bacteriocin sensitivity and were mostly serotype II or non-typable.

Conclusions:

• The distinct phenotypic and genotypic characteristics suggest that Streptococcus agalactiae from humans and cattle constitute separate populations.
• These findings support the hypothesis of independent evolutionary trajectories despite sharing the Group B antigen.