Haemophilus haemolyticus: a human respiratory tract commensal to be distinguished from Haemophilus influenzae.
BACKGROUND
Haemophilus influenzae is a common pathogen in adults with chronic obstructive pulmonary disease (COPD). In a prospective study, selected isolates of apparent H. influenzae had an altered phenotype. We tested the hypothesis that these variant strains were genetically different from typical H. influenzae.


METHODS
A prospective study of adults with COPD was conducted. Strains of apparent H. influenzae obtained from a range of clinical sources were evaluated by ribosomal DNA sequence analysis, multilocus sequence analysis, DNA-DNA hybridization, and sequencing of the conserved P6 gene.


RESULTS
Variant strains were determined to be Haemophilus haemolyticus by means of 4 independent methods. Analysis of 490 apparent H. influenzae strains, identified by standard methods, revealed that 39.5% of sputum isolates and 27.3% of nasopharyngeal isolates were H. haemolyticus. Isolates obtained from normally sterile sites were all H. influenzae. In a prospective study, acquisitions of new strains of H. haemolyticus were not associated with exacerbations of COPD, whereas 45% of acquisitions of new strains of H. influenzae were associated with exacerbations.


CONCLUSIONS
Standard methods do not reliably distinguish H. haemolyticus from H. influenzae. H. haemolyticus is a respiratory tract commensal. The recognition that some strains of apparent H. influenzae are H. haemolyticus substantially strengthens the association of true H. influenzae with clinical infection.
Murphy
Timothy F
TF
Department of Medicine, University at Buffalo, State University of New York, Buffalo, NY, USA. murphyt@buffalo.edu
Brauer
Aimee L
AL
Sethi
Sanjay
S
Kilian
Mogens
M
Cai
Xueya
X
Lesse
Alan J
AJ
D006190:Haemophilus / Q000145:classification* / Q000302:isolation & purification*; D006192:Haemophilus Infections / Q000453:epidemiology / Q000382:microbiology*; D006193:Haemophilus influenzae / Q000145:classification / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D010802:Phylogeny; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications*; D012141:Respiratory Tract Infections / Q000382:microbiology*; D013183:Sputum / Q000382:microbiology