Survival of nontypeable Haemophilus influenzae in macrophages

In this study we have investigated the ability of nonencapsulated, nontypea ble Haemophilus influenzae, NT477 to survive in the J774 mouse macrophage-l ike cell line. Viable, intracellular nontypeable H. influenzae could still be recovered from macrophages 72 h after phagocytosis. In contrast, H. infl uenzae strain Rd, an avirulent, nonencapsulated variant of a serotype d str ain, was killed within 24 h. These differences suggest that NT477, in compa rison to Rd, possesses unique attributes that enable it to survive in macro phages for prolonged periods. To determine whether this trait is ubiquitous amongst nontypeable H. influenzae, 33 primary clinical isolates obtained f rom children with otitis media were screened for their ability to survive i n macrophages. Of these isolates, 82% were able to persist in an intracellu lar environment for periods of at least 24 h. The number of viable organism s recovered at this time ranged from 2 X 10(4) to 50 colony-forming units p er strain indicating that the extent to which nontypeable H. influenzae can resist macrophage-mediated killing varies between strains. (C) 2001 Federa tion of European Microbiological Societies. Published by Elsevier Science B .V. All rights reserved.