Biotype of Haemophilus influenzae: Correlation with Virulence and Ampicillin Resistance

Biotype and serotype were determined for 473 isolates of Haemophilus influenzae from 399 children. Patients with invasive disease usually had serotypable (86%) and biotype 1 (80%) isolates. Respiratory isolates from well children and children whose illness was not caused by H. influenzae were rarely serotypable (1%) or biotype 1 (8%o). Respiratory isolates from children whose illness was possibly or probably related to H. influenzae and isolates from children with cystic fibrosis were more frequently biotype 1, serotypable, or both (P < 0.01 for all comparisons). Ten (67%) of 15 children with acute otitis media due to H. influenzae had tympanocentesis isolates which were biotype 1; only one isolate was serotypable. Isolates from inflamed conjunctivae had biotypes and serotypes similar to respiratory isolates from well children. Ampicillin resistance was less frequent among biotype 1 isolates (9%) compared with other biotypes (19%) (P < 0.01). The data suggest that H. influenzae is biochemically heterogeneous and that noncapsular factors, frequently predictable by biotype, contribute to virulence. Haemophilus influenzae is a pleomorphic gramnegative coccobacillus which is defined by lack of codehydrogenase activity and inability to synthesize porphyrin from 6-aminolevulinic acid. There is a striking dichotomy of virulence within the species. H. influenze is both the major cause of meningitis, pyogenic arthritis, and facial and orbi