Summary: Opacity (Opa) proteins are a family of antigenically variable outer-membrane proteins of ET-37 complex meningococci, defined by multilocus enzyme electrophoresis, have been isolated on different continents. Twenty-six different Opa proteins have been observed within strains of the ET-37 complex isolated between the 1960s and the 1980s, although individual strains have only four genes per chromosome. In this work the genes of four closely related ET-37 complex strains recently isolated from Mali, West Africa were characterized and compared with the genes of strain FAM18, an ET-37 complex isolate from the USA. DNA sequence analysis and Southern blot experiments indicated that recombinational reassortment, including gene duplication and import by horizontal genetic exchange, has occurred in the genes within the ET-37 complex, resulting in two partially different Opa repertoires being present in FAM18 and the Mali isolates. Using synthetic peptides derived from the hypervariable (HV) regions of genes, the epitopes for nine mAbs were mapped. These bacteria, isolated on different continents, contain both shared and unique HV regions encoding epitopes recognized by mAbs and show evidence of recombinational reassortment of the HV regions.


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