Identification and genetic characterization of Haemophilus influenzae genetic island 1

The type b capsule of pathogenic Haemophilus influenzae is a critical facto r for H. influenzae survival in the blood and the establishment of invasive infections. Other pathogenic factors associated with type b strains may al so play a role in invasion and sustained bacteremia, leading to the seeding of deep tissues. The gene encoding haemocin is the only noncapsular gene f ound to be specific to type b strains until now were we report the discover y of an approximately 16-kb genetic Locus, HiGI1, that is present primarily in type b strains. Pulsed-field gel electrophoresis and Southern hybridiza tion were used to map this new locus between secG (HI0445) and fruA (HI0446 ), which are contiguous in Rd, a nonpathogenic derivative of a serotype d s train. It is inserted at the 3' end of tRNA(4)(Leu) and has regions whose G +C content differs from the average genomic G+C content of H. influenzae. A n integrase gene, which encodes a CP4-57 like integrase, is located downstr eam of tRNA(4)(Leu). Hybridization probes based on the sequences within the HiGI1 locus have been used to screen 61 H. influenzae strains (2 type a, 2 2 type b, 2 type c, 1 type d, 3 type e, 7 type f, and 21 nontypeable H. inf luenzae [NTHi]) from our collection This HiGI1 locus exists in all 22 type b strains and two NTHi strains and is likely to have been acquired by an an cestral type b strain.