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

Departments of Microbiology/Immunology and Allegheny University of the Health Sciences, and St Christopher's Hospital for Children,PA 19129, USA Departments of Pediatrics,Allegheny University of the Health Sciences, and St Christopher's Hospital for Children,PA 19129, USA Departments of Philadelphia, PA 19129, USA ABSTRACT 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 (hmcl) revealed several features common to class II bacteriocins of certain Gram-positive bacteria. Mutagenesis of the open reading frame immediately upstream of hmcl resulted in a loss of the HMC production phenotype. When an HMC-producing strain of H. influenzae and the HMC-deficient isogenic mutant were compared for invasion in 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. * Author for correspondence: John J. LiPuma. Tel: +1 215 842 6688. Fax: +1 215 848 2271. Keywords: Haemophilus influenzae, bacteriocin, haemocin Present address: Infectious Disease Unit, Department of Medicine, Massachusetts General Hospital, Boston, MA 02114, USA.