What Causes Gamma Haemolytic Streptococcus Infection?

Hi Doctor, My name is Judith and my 8 year old Jarett has an infection called gamma haemoltic Streptococcus and his Doctor Pediatrician wants to give him a 10 days dose of it. 1) what is it for and should an 8year old be able to tolerate it. His blood and stool samples are okay otherwise.