D-078. A Subset of Strains of Haemophilus influenzae with the IgA1 Protease B Gene Are Clonally Related
Nontypeable Haemophilus influenzae is an important cause of respiratory tract infection in adults with chronic obstructive pulmonary disease (COPD). H. influenzae shows enormous genetic diversity among strains. The differential genome content of strains of H. influenzae is an important determinant of whether a patient with COPD experiences an episode of infection or an episode of asymptomatic colonization following acquisition of a new strain. Approximately half of strains of H. influenzae isolated from adults with COPD contain a newly discovered IgA1 protease gene, igaB, that is separate and distinct from the IgA protease gene, iga, that is present in all strains of H. influenzae. To characterize the genetic relationship of COPD strains that contain the igaB gene, we subjected 10 such strains to multilocus sequence typing (MLST). Surprisingly, 7 strains that contain the igaB gene that were recovered from epidemiologically unrelated patients as part of a prospective study of COPD all had the same MLST type and the other 3 strains had closely related MLST types. To further assess the relatedness of the strains, the 1.4 kb 16S rDNA fragment was amplified by PCR and the sequence was determined. All 10 strains and an additional 10 COPD strains that contain the igaB gene showed similar 16S rDNA sequences compared to one another. Analysis of these 20 strains with ~150 H. influenzae strains in a bootstrap consensus tree based on 16S rDNA sequences revealed that some but not all COPD strains that contain the igaB gene are closely related. The strains with related MLST types clustered together in the dendrogram based on 16S rDNA. We conclude that a subset of COPD strains that contain the igaB gene represents a clonal group of nontypeable H. influenzae.