Relationships of nontypeable Haemophilus influenzae strains to hemolytic and nonhemolytic Haemophilus haemolyticus strains.
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.
Department of Epidemiology, University of Michigan School of Public Health Tower, 109 Observatory, Ann Arbor, MI 48109-2029, USA. sigmb@med.umich.edu
Kirk W
KW
McCrea
Jingping
J
Xie
Nathan
N
LaCross
Mayurika
M
Patel
Deepa
D
Mukundan
Timothy F
TF
Murphy
Carl F
CF
Marrs
Janet R
JR
Gilsdorf
D000328:Adult; D001426:Bacterial Proteins / Q000235:genetics*; D002675:Child, Preschool; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D005798:Genes, Bacterial / Q000235:genetics; D006190:Haemophilus / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D006192:Haemophilus Infections / Q000382:microbiology; D006801:Humans; D007223:Infant; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA; D012697:Serine Endopeptidases / Q000235:genetics
D001426:Bacterial Proteins; D004269:DNA, Bacterial; C102237:lic2A protein, Haemophilus influenzae; D012697:Serine Endopeptidases; C021433:IgA-specific serine endopeptidase