Comparison of Haemophilus paragallinarum isolates by restriction endonuclease analysis of chromosomal DNA

Chromosomal DNA from Haemophilus paragallinarum was examined by restriction endonuclease analysis (REA) using the enzymes BamHI, EcoRI, HindIII, or SmaI. The enzyme SmaI had no apparent effect upon the DNA from eight representative H. paragallinarum isolates. The remaining enzymes cut the H. paragallinarum DNA to varying degrees, with the most useful patterns for distinguishing isolates being given by HindIII. The REA patterns given by HindIII were stable under both in vitro and in vivo conditions. The use of the enzyme HindIII showed that eight Australian isolates of H. paragallinarum were genetically similar. In contrast, 14 isolates of H. paragallinarum from outside Australia were markedly different from each other and the Australian isolates. A plasmid of approximately 6 kilobase pairs in size was found in one isolate of H. paragallinarum.