Antimicrobial drug resistance and the occurrence of plasmids in Haemophilus paragallinarum

A broth microdilution method was used to examine the sensitivity of 75 Haemophilus paragallinarum isolates to six antimicrobial drugs (ampicillin, erythromycin, neomycin, penicillin, streptomycin, and tetracycline). A total of 55 of the isolates (73%) were sensitive to all six drugs. The remaining 20 isolates were resistant to streptomycin, with one of these isolates also being resistant to tetracycline and another also resistant to neomycin. No isolate showing antimicrobial drug resistance belonged to agglutinin serovar C, despite this being the single largest serovar (27 out of 75) in the study. No plasmids were detected among the 75 isolates, despite the use of five different plasmid-screening techniques.