Prevalence and distribution of adhesins in invasive non-type b encapsulated Haemophilus influenzae

Adhesion to the respiratory epithelium plays an important role in Haemophilus influenzae infection. The distribution of H. influenzae adhesins in type b and nontypeable strains has been characterized, but little is known about the prevalence of these factors in non-type b encapsulated strains. We analyzed 53 invasive type a, type e, and type f strains for the presence of hap, hia, hmw, and hif genes; Hap, Hia, and HMW1/2 adhesins; and hemagglutinating pili. The hap gene was ubiquitous, and homologs of hmw and hia were present in 7 of 53 (13.2%) and 45 of 53 (84.9%) strains, respectively. Hap was detected in 28 of 45 (62.2%) hap(+) strains, HMW1/2 was detected in 5 of 7 (71.4%) hmw(+) strains, and Hia was detected in 31 of 45 (68.8%) hia(+) strains. The hif gene cluster was present in 26 of 53 strains (49.1%), and 21 of 26 hif(+) strains (80.8%) agglutinated (HA) red blood cells. Nine isolates exhibited HA but lacked the hif gene cluster. The distribution of adhesin genes correlated with the genetic relatedness of the strains. Strains belonging to one type a clonotype and the major type e clonotype possessed hia but lacked the hif cluster. Strains belonging to the second type a clonotype possessed both hia and hif genes. All type f strains belonging to the major type f clonotype possessed hia and lacked hifB. Although the specific complement of adhesin genes in non-type b encapsulated H. influenzae varies, most invasive strains express Hap and Hia, suggesting these adhesins may be especially important to the virulence of these organisms.