Plasmid linked ampicillin resistance in Haemophilus influenzae type b

Abstract

4 ampicillin resistant, β lactamase producing strains of Haemophilus influenzae type b were examined for the presence of plasmid deoxyribonucleic acid (DNA). 3 resistant strains contained a 30x106 dalton (30 Mdal) plasmid and 1 resistant strain contained a 3 Mdal plasmid. The ampicillin sensitive Haemophilus strains examined did not contain plasmid DNA. Transformation of a sensitive H. influenza strain to ampicillin resistance with isolated plasmid DNA preparations revealed that the structural gene for β lactamase resided on both plasmid species. DNA DNA hybridization studies showed that the 30 Mdal Haemophilus plasmid contained the ampicillin translocation DNA segment (TnA) found on some R factors of enteric origin. The significance of this finding is discussed in relation to the possible origin of the H. influenzae plasmids.