Cloning of the haemocin locus of Haemophilus influenzae type b and assessment of the role of haemocin in virulence.

The bacteriocin haemocin (HMC) is produced by most type b strains of Haemophilus influenzae, including strains determined to be genetically diverse, and is toxic to virtually all non-type b strains of H. influenzae, both encapsulated and non-encapsulated. Examination of the deduced amino acid sequences of several genes upstream of the previously identified HMC immunity gene (hmcI) revealed several features common to class II bacteriocins of certain Gram-positive bacteria. Mutagenesis of the open reading frame immediately upstream of hmcI resulted in a loss of the HMC production phenotype. When an HMC-producing strai of H. influenzae and the HMC-deficient isogenic mutant were compared for invasion on the infant-rat model, the HMC-producing strain was found to invade significantly earlier; however, a significantly higher number of rats infected with the isogenic mutant became bacteraemic as compared with those infected with the HMC-producing parent.