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

Abstract

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.Haemophilus influenzae is one of eight Haemophilus species that reside as commensal organisms in the pharyngeal cavity of humans. These other commensal Haemophilus species include H. parainfluenzae, H. haemolyticus, H. parahaemolyticus, H. paraphrohaemolyticus, H. segnis, H. aphrophilus, and H. paraphrophilus. H. influenzae is by far the most pathogenic member of the genus in humans. Strains possessing a type b capsule are often associated with invasive diseases, such as meningitis, sepsis, and pneumonia; and strains lacking a capsule (referred to as nontypeable [NT]) are associated with localized mucosal diseases, such as otitis media, sinusitis, and bronchitis. Other haemophili are considered to be rarely associated with disease, and H. haemolyticus has never been implicated as an infectious disease agent (1).In contrast to other haemophili, H. haemolyticus and H. influenzae both depend on X (hemin) and V (NAD) growth factors, both lack the ability to ferment sucrose, both share similar GϩC contents, and both are nearly indistinguishable by their colony and cellular morphologies (25). Initial phylogenetic studies performed by using DNA-DNA hybridization revealed that H. haemolyticus associated with H. influenzae in a cluster of the family Pasteurellaceae termed Haemophilus sensu stricto (6,41,47), and t...

Difficult identification ofHaemophilus influenzae, a typical cause of upper respiratory tract infections, in the microbiological diagnostic routine

“…Biochemical assays have been shown to lack reliability [6,17,[20][21][22][23][24][25][26][27][28]. Complex multiplex PCR-approaches [38] or sequence-based approaches [5] are hardly realistic for the routine setting because such procedures are both expensive and demanding regarding hands-on time of technical laboratory assistants.…”

“…Growth factor-based methods make use of the fact that H. infl uenzae lacks the enzymatic capacity to convert δ-aminolevulinic acid (ALA) to protoporphyrin, hence, depends on factor X (heme) for growth [20,21]. For the identifi cation of H. infl uenzae, in particular, X-and V-factor (nicotinic acid diamine, NAD) dependence is usually assessed [20,22] but does not allow for the discrimination of H. haemolyticus from H. infl uenzae.…”

“…A majority of H. haemolyticus strains causes α-hemo lysis on horse, cow, or rabbit blood agar [22][23][24], which H. influenzae cannot do. Unfortunately, H. haemolyticus does not show this phenomenon on sheep blood agar, which is most frequently used in microbiological routine diagnostics, considerably reducing the practical relevance.…”

Simultaneous Identification of Haemophilus Influenzae and Haemophilus Haemolyticus using Real-Time PCR

“…Genetically, NTHi undergoes high levels of lateral gene transfer with other species, usually with other Haemophilus spp. but occasionally with other genera [7][8][9][10]. The promiscuity of the NTHi genome has greatly impeded prior attempts to specifically target this species using DNA-based methods, most notably when RESEaRch aRticlE Price, Harris, Spargo et al future science group attempting to differentiate H. influenzae from H. haemolyticus.…”

Chronic Otitis Media: Microbial Environment During Viral Infection and Genetics of Host Susceptibility

“…Haemophilius influenzae, a known pathogen, and its closest phylogenetic relative Haemophilus haemolyticus, a commensal bacterium. 174,175 PCoA of the nasopharyngeal microbiome samples along with samples from various other body habitats showed logical clustering with similar locations throughout the URT. The nasopharynx, adenoid, ear, hair, and nostril samples all formed a single large cluster.…”