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.