Re: Opportunistic pathogens
For opportunistic pathogens to cause a problem doesn't require suppression of the immune system; it can simply be that something that's harmless in one place is harmful in another. I've recently found this through personal experience, having had shoulder surgery in which one of the incisions happened to pass through a hair follicle, thus pushing propionibacterium acnes (the pathogen that causes acne, but otherwise lives as a harmless commensal in hair follicles) deeper into my body, causing an obvious majorly inflamed area and a risk of arthritis in two years if it got into the joint capsule. The treatment was six weeks of intravenous antibiotics. I normally shake off infections fairly quickly, so it's not as if my immune system was compromised.
(There's an interesting experimental preventative treatment for this problem, by the way: seal the skin with cyanoacrylate, thus gluing the bacteria into place.)
I guess they'll carry quite a range of antibiotics, and a quick google search indicates that crew medical officers are trained to insert IV lines. I don't know what they'd do about the equivalent of a drip chamber in zero-g, but I'm sure someone's found a way round that one.