Characterization of non-type B Haemophilus influenzae strains isolated from patients with invasive disease

Forty-one non-type b Haemophilus influenzae isolates from cases of invasive disease were characterized. By PCR capsular genotyping, 33 nonencapsulated strains, 4 type f isolates, and 4 b2 strains were identified. By pulsed-field gel electrophoresis, the nonencapsulated isolates exhibited great genetic heterogenicity, whereas the type f and the b2 strains seemed to have a clonal spread. Occurrence of the hifA gene was found by PCR in 18 % of the nonencapsulated, 50 % of the b2, and all of the type f strains. Hemagglutinating fimbriae were generally expressed by nonencapsulated isolates when fimbrial gene hifA was present. Two nonencapsulated isolates not susceptible to ampicillin were detected; no strains were positive for b-lactamase production. Haemophilus influenzae is responsible for a variety of local-ized respiratory tract infections and invasive diseases (e.g., meningitis, septicemia, epiglottitis, and septic arthritis) (29). Invasive disease is associated with a minority of virulent strains, generally encapsulated H. influenzae serotype b (Hib) (35); however, other serotypes or nonencapsulated strains have also been found responsible. With the advent of effective conju-gated vaccines against the Hib capsular antigen, serotype