Prevalenceof hicAB, lav, traA , and hifBC among Haemophilus in£uenzae middle earand throat strains

Bacterial colonization of the upper respiratory tract is the first step in the pathogenesis of Haemophilus influenzae (Hi) infection. Haemophilus influenzae carriage rates vary between 25% and 84% in children, and colonization is a very dynamic process characterized by rapid bacterial turnover and carriage of multiple Hi strains (Trottier et al., 1989; Faden et al., 1991; Dhooge et al., 2000; St Sauver et al., 2000; Farjo et al., 2004). In addition to asymptomatic colonization, NTHi are important causes of respiratory infections in humans, including acute otitis media. NTHi causes between 30% and 52% of acute otitis media in children (Eskola & Kilpi, 2000). Haemophilus influenzae display significant strain-tostrain genetic diversity (Gilsdorf, 1998) and horizontal (lateral) gene transfer contributes significantly to maintenance of that diversity (Weiser, 2000). Munson et al. (2004), using in silico subtraction and bioinformatics techniques, reported the presence of several genes, including hic, lav, and tnaA, in two H. influenzae strains isolated from children with otitis media and absent in the fully sequenced H. influenzae strain Rd (Fleischmann et al., 1995) and suggested these genes may play a role in H. influenzae pathogenesis. Interestingly, hic, lav, and tnaA appear to have undergone lateral gene transfer between NTHi and other bacteria (Martin et al., 1998; Mhlanga-Mutangadura et al., 1998; Davis et al., 2001). In addition, evolutionary studies of Hi suggest that the hif cluster has also undergone lateral gene transfer (Mhlanga-Mutangadura et al., 1998). To better understand the potential role of these laterally transferred genes in otitis media pathogenesis, a population-based gene prevalence analysis was used, which has proved useful in identifying H. influenzae genes retained during natural selection among middle-ear isolates and not among throat isolates (Pettigrew et al., 2002). The hif gene cluster, responsible for the biosynthesis of hemagglutinating pili, is located between purE and pepN on the H. influenzae chromosome and contains five genes (hifA through hifE). hifA encodes the major pilus structural protein, hifB encodes the subunit chaperone protein, hifC encodes an usher (assembly platform ) protein, hifD encodes