In-vitro susceptibility of thirty strains of Haemophilus ducreyi to several antibiotics including six cephalosporins.

We have studied the in-vitro susceptibility of 30 strains of Haemophilus ducreyi to 22 antibacterial agents. Twenty-seven strains produced a beta-lactamase that had an isoelectric point similar to the isoelectric point of the TEM 1 type beta-lactamase produced by pSF 2124. Except for cefamandole, the 30 strains had similar susceptibilities to the different cephalosporins, cefotaxime being the most active compound. Twenty-two isolates were resistant to tetracycline and doxycycline; minimal inhibitory concentration (MIC) of minocycline was 4 mg/l for all the strains. One isolate was resistant to chloramphenicol (MIC = 16 mg/l). All strains were relatively resistant to colistin and nalidixic acid, and susceptible to streptomycin, kanamycin, gentamicin, erythromycin, rifampicin and vancomycin.