Adherence of Haemophilus influenzae to respiratory epithelial cells is the first step in the pathogenesis of H. influenzae infection and is facilitated by the action of several adhesins located on the surface of the bacteria. In this study, prevalences of hifBC, which represent the pilus gene cluster; hmw1A, hmw2A, and hmwC, which represent high-molecular-weight (HMW) adhesin genes; and hia, which represents H. influenzae adhesin (Hia) genes were determined among clinical isolates of encapsulated type b (Hib) and nonencapsulated (NTHi) H. influenzae. hifBC genes were detected in 109 of 170 (64%) Hib strains and in 46 of 162 (28%) NTHi isolates (P ‫؍‬ 0.0001) and were more prevalent among the invasive type b strains than invasive NTHi strains (P ‫؍‬ 0.00003). Furthermore, hifBC genes were significantly more prevalent (P ‫؍‬ 0.0398) among NTHi throat isolates than NTHi middle ear isolates. hmw1A, hmw2A, hmwC, and hia genes were not detected in Hib strains. Among NTHi isolates, the prevalence of hmw1A was 51%, the prevalence of hmw2A was 23%, the prevalence of hmwC was 48%, and the prevalence of hia was 33%. The hmw genes were significantly more prevalent among middle ear than throat isolates, while hia did not segregate with a respiratory tract site. These results show the variability of the presence of adhesin genes among clinical H. influenzae isolates and suggest that hemagglutinating pili may play a larger role in H. influenzae nasopharyngeal colonization than in acute otitis media whereas the HMW adhesins may be virulence factors for acute otitis media.Haemophilus influenzae organisms are gram-negative bacilli characterized by the presence or absence of a polysaccharide capsule; strains that bind antibodies directed against one of six capsular types are designated serotypes a to f and strains that do not bind these antibodies are designated nontypeable. H. influenzae possessing the type b capsule (Hib) causes serious invasive infections such as meningitis, epiglottitis, septic arthritis, and facial and periorbital cellulitis accompanied by bacteremia in nonimmune individuals, while nontypeable H. influenzae (NTHi) possessing no capsule are important causes of nonbacteremic respiratory infections such as acute otitis media, sinusitis, and bronchitis.

High-molecular-weight proteins of Haemophilus influenzae mediate attachment to epithelial cells. Previous reports describe several allelic versions of hmwA genes that have different adherence properties. Here we report three new alleles of hmwA (hmwA from strain AAr96, hmwA from strain AAr105, and hmwA from strain G822), demonstrating the high degree of DNA variation of these genes among different strains.Nontypeable Haemophilus influenzae (NTHi), a gram-negative, nonencapsulated, human-specific microorganism, commonly inhabits the upper respiratory tract and causes otitis media, conjunctivitis, sinusitis, pneumonia, and acute exacerbation of chronic bronchitis. Occasionally, NTHi causes severe invasive diseases, such as meningitis, endocarditis, and bacteremia (14).NTHi high-molecular-weight (HMW) proteins mediate bacterial attachment to epithelial cells (7,11,17,18) and have been implicated as possible virulence factors for otitis media (12,20) or chronic obstructive pulmonary disease (21). This adhesin is produced by the action of three genes (hmwA, hmwB, and hmwC) located in the hmw locus (1, 2). Many H. influenzae strains contain two distinct hmw loci, hmw-1 and hmw-2 (3, 4). The hmwA genes of these loci encode the HMWA adhesive proteins, which are 52 to 62% identical at the amino acid level (4) among several NTHi strains. hmwB genes encode outer membrane translocator proteins, which are 99% identical in NTHi strain 12. HMWB proteins are located in the outer membrane and serve to translocate HMWA across the outer membrane and prevent degradation by periplasmic proteases. hmwC genes encode cytoplasmic proteins, which are 97% identical in NTHi strain 12, and appear to stabilize HMWA (2, 17) and to influence glycosylation of HMWA1 (10). HMWA1 of strain 12 mediates binding to ␣-2,3-linked sialylated glycoproteins, and the epithelial cell receptor structure for HMWA2 of this strain is unknown (17).While initial studies of hmwA described the alleles hmwA1 and hmwA2, one in each hmw locus of strain 12 (3), Van Schilfgaarde et al. (21) described a third hmwA allele from the chronic obstructive pulmonary disease H. influenzae strain A950006, whose 4,671-bp gene encodes a predicted protein with 70% homology to HMWA1 and 68% homology to HMWA2 of strain 12. More recently, Buscher et al. (4) have identified four additional hmwA alleles with either HMWA1-or HMWA2-like binding characteristics from two NTHi strains and showed that the genes encoding these differential binding characteristics were variably located downstream of either HI01679 or HI01598 in the Rd genome.Although type b strains lack hmw loci, 55 to 80% of NTHi strains have these genes (1,8,20). Among the other encapsulated H. influenzae types, hmw loci were detected in 26% of type a, 8% of type e, and 5% of type f strains (16). In a previous study by our group using dot blot hybridization, 51% of NTHi isolates hybridized with strain 12 hmwA1-specific probes, 23% hybridized with hmwA2-specific probes, and 48% hybridized with hmwC-specific probes (8). While 18...