A VIRULENT NONENCAPSULATED HAEMOPHILUS-INFLUENZAE

Nontypeable Haemophilus influenzae strain INT1 was isolated from the b lood of a young child with clinical signs of meningitis following acut e otitis media, No immunologic or anatomic predisposition of this chil d for invasive bacterial infection with an unusual organism was docume nted, Sensitive ELISA proved the absence of intra- or extracellular ca psular polysaccharide production by INT1, and Southern blot analysis c onfirmed the lack of an intact capsulation (cap) gene locus within the chromosome. Nevertheless, INT1 established bacteremia and meningitis in infant and weanling rat models of invasive H, influenzae infection. High-molecular-weight DNA isolated from INT1 was shown to confer an i nvasive phenotype on transformation of a nonencapsulated, avirulent la boratory strain of H. influenzae. Together these findings imply the pr esence of one or more as-yet-undiscovered, noncapsular virulence facto rs of H. influenzae that are capable of mediating invasive disease and resistance to immunologic clearance.