My guinea pig has a bacterial infection, is it deadly?

My guinea pig has a bacterial infection. The are at least 8 red scabs on his skin. Around the areas are red skin and mose of the hair is gone around the areas. On Wednesday I toke him to the vet. We got an anti-biotic. I've already lost his brother from an URI and almost lost him to the same thing. My question is, will this kill him?