How do people treat group b streptococcal infection?

Penicillin. Penicillin is the drug of choice for grouop b streptococcus infections. For those allergic to penicillins there are other antibiotic choices that are effective. The route of administration and the duration of the treatment would depend on the nature, location, and severity of the infection.
Penicillin. It depends what you mean. If you are treating a soft tissue infection the antibiotic of choice is oral penicillin or cephalosporin. If you mean gbs + colonization of the genital tract during pregnancy, then this is treated with IV penicillin until delivery.