Hen may have sometype of infection. Best antibiotic to use

[sweetpeasmom]

I have a hen that I posted about a few days ago. I am just guessing about what is wrong with her. I think that the infestation of lice and mites was so bad that the feathers on her bum died and fell off and got infected. Bottom is extremely swollen. I was thinking that I could get an injectable antibiotic the inject directlly into the swollen area. I figure that she is going to probably die anyways so I am just stabbing in the dark trying to help her. The reason is that I have several other hens that are starting to show signs the same signs as this hen. Any suggestions on what type of antibiotic to use would be appreciated. Thanks