True. I don't know the specific combination used, but Dan did mention
that the cocktail contained three.  It's a good question. "Shotgun"
therapy for an unknown infection tends to vary with the geographic
region.

Macrolides, fluoroquinolones, and tetracyclines all have activity.  
While I'd tend to think of a basic cocktail around here as a
penicillinase-resistant semisynthetic penicillin or a third-generation
cephalosporin, an aminoglycoside and metronidazole, the vet could have
used azithromycin rather than a beta-lactam drug, and/or a
fluoroquinolone rather than, say, gentamicin.