Plasmid-Mediated Ampicillin Resistance in Haemophilus ducreyi

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Abstract
Three of 19 strains of Haemophilus ducreyi , isolated during a recent outbreak of chancroid, were found to produce β-lactamase and to harbor a 6.0 × 10 6 -dalton plasmid. Escherichia coli transformed with this plasmid acquired β-lactamase-mediated resistance to ampicillin. The guanine-plus-cytosine content of the plasmid was found to be 41 mol%. Restriction endonuclease digestion studies suggest that a relatively large portion of the Tn 1 translocon is carried by this plasmid. Whereas this plasmid could not be transferred to H. influenzae by mating on membrane filters, a strain of H. ducreyi was able to receive and donate a 30 × 10 6 -dalton ampicillin resistance plasmid from H. influenzae . The ability of H. ducreyi to receive and donate conjugative plasmids may result in the appearance of multiply resistant strains.