Phenotypic and molecular characterization of V-factor (NAD)-independent Haemophilus paragallinarum

Abstract

In South Africa from early 1989, strains of Haemophilus paragallinarum not requiring nicotinamide adenine dinucleotide (NAD) have been isolated from commercial chickens suffering from infectious coryza. 15 of these field isolates were characterized by biochemical typing, serotyping, restriction endonuclease analysis (REA), and ribotyping. The isolates were chosen to represent diversity in geographic location, time of disease outbreak, and type of flock. All were typical of the species in biochemical properties, except that they were NAD-independent and all were Page serovar A. REA was performed with 3 enzymes: HindIII, HpaII, and SspI. All isolates gave identical REA profiles with all 3 enzymes. Ribotyping was performed using a probe that consisted of the plasmid pUC19 into which the 16s rRNA operon of H. paragallinarum had been inserted. All 15 isolates gave the same ribotyping profile using each of the 3 enzymes. As a group the NAD-independent strains gave REA profiles and ribotypes that were very different from a range of classic South African strains isolated before 1989. These results strongly suggest that the NAD-independent isolates are clonal in nature.