The Moraxella bovis RTX toxin locus mbx defines a pathogenicity island

To characterize flanking regions of the mbx operon in Moraxella bovis, DNA surrounding mbxCABDtolC was sequenced in haemolytic and nonhaemolytic strains of M. bovis. In two haemolytic strains of M. bovis, the mbx operon, including the adjacent M. bovis tolC orthologue, was flanked by approximately 700 bp imperfect repeats. Nonhaemolytic strains of M. bovis had only one or no such repeats, as well as ORFs identical to those flanking the repeats from haemolytic M. bovis. Two nonhaemolytic strains also contained ORFs with deduced amino acid sequence similarity to bacterial araJ genes. The G + C content of the mbxCABDtolC gene region was lower than the flanking regions. The genetic organization and G + C content of mbxCABDtolC genes, and flanking repeats in haemolytic M. bovis, as well as the presence or absence of flanking repeats in nonhaemolytic M. bovis, suggests that this RTX operon is located on a mobile genetic element, and supports the designation of this region as a pathogenicity island, which is believed to be the first such element demonstrated in M. bovis.