Fimbriation of Haemophilus Species Isolated from the Respiratory Tract of Adults

Twenty-two clinical isolates of Haemophilus species were studied within two passages of their original isolation for the presence of fimbriae by negative-staining electron microscopy. Six isolates were identified as fimbriated, including three strains of nontypable Haemophilus inf!uenzae, one strain of Haemophilus parainjluenzae, and two strains of Haemophilus haemolyticus. In fresh isolates of fimbriated strains of nontypable H. inf!uenzae, ∼40%–50% of cells had fimbriae; after five passages in vitro,