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Journal of Clinical Microbiology, February 2008, p. 406-416, Vol. 46, No. 2
0095-1137/08/$08.00+0     doi:10.1128/JCM.01832-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Relationships of Nontypeable Haemophilus influenzae Strains to Hemolytic and Nonhemolytic Haemophilus haemolyticus Strains

Kirk W. McCrea,^1* Jingping Xie,¹ Nathan LaCross,¹ Mayurika Patel,¹ Deepa Mukundan,^1, Timothy F. Murphy,³ Carl F. Marrs,² and Janet R. Gilsdorf^1,2

Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, Michigan,¹ Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, Michigan,² Department of Medicine, University at Buffalo, State University of New York, Buffalo, New York³

Received 14 September 2007/ Returned for modification 5 November 2007/ Accepted 14 November 2007

Haemophilus influenzae is both a human respiratory pathogen and pharyngeal commensal, while H. haemolyticus, the closest phylogenetic relative of H. influenzae, is arguably a strict pharyngeal commensal. A hemolytic phenotype has historically differentiated H. haemolyticus from H. influenzae, but the recent recognition of significant nonhemolytic H. haemolyticus colonization has decreased this trait's resolvability. Given this and the potential of recombination between the species, we examined the distribution of microbiologic and molecular traits between collections of H. influenzae and H. haemolyticus strains separated within a dendrogram obtained by multilocus sequence analysis (MLSA). All strains hybridizing with a probe to iga, a gene encoding an immunoglobulin A protease of H. influenzae, clustered apart from strains that did not hybridize with the probe. Other traits also segregated significantly along this division, suggesting a separation of the species. Of note, the LOS genes licA, lic2A, and lgtC of H. influenzae were approximately 2, 6, and 54 times, respectively, more prevalent in H. influenzae than in H. haemolyticus. In contrast to species separation, interspecies recombination was evidenced by the inability of single gene sequences to phylogenetically separate the species and by the "fuzzy" distribution of some species-specific traits across the species dividing line. Together, these data support the historically accurate and pragmatic division of these species while recognizing their potential for recombination. Future comparative genomic studies identifying common and distinctive genes could be useful in evaluating their role in the commensal or virulent growth, respectively, of H. influenzae.

Published ahead of print on 26 November 2007.

Present address: Department of Pediatrics, University of Toledo College of Medicine, Toledo, OH.