Susceptibility of Hemophilus parapertussis to Certain Antibiotics.

The susceptibility of 12 strains of H. parapertussis to certain antibiotics was examined. In vitro, the order of decreasing activity was, polymyxin B, terramycin, chloramphenicol, aureomycin, neomycin, penicillin and streptomycin. There was little variation in the response to any one antibiotic of the various strains tested. In vivo, listed in the order of their decreasing effectiveness against the experimental murine infection were polymyxin B, aureomycin, terramycin, neomycin, chloramphenicol and streptomycin. Compared with H. pertussis, H. parapertussis was more resistant to each antibiotic tested in vitro. In vivo, similar degrees of effectiveness were exhibited against the two organisms by polymyxin B, terramycin and chloramphenicol; the first two named being particularly effective both in vitro and in vivo.