The effect of mutations in genes required for lipopolysaccharide synthesis on Haemophilus influenzae type b colonization of human nasopharyngeal tissue

Haemophilus influenzae type b (Hib) is an upper respiratory tract commensal that can cause invasive disease, particularly in young children. Lipopolysaccharide (LPS) has been implicated as a major virulence determinant of Hib, and changes in LPS structure may influence bacterial interactions with the respiratory mucosa. We have examined the effect of variations in IFS on the interaction of Hib with human nasal turbinate tissue maintained in an organ culture model with an air-interface, by using isogenic derivatives of strains RM153 (Eagan) and RM7004 expressing truncated LPS due to mutations in genes contained within the chromosomal loci lic1 and lic2 (lic1 lic2) or in the galE and galK genes (galEK). Tissue was infected with an inoculating dose of 2.3-3.3 x 10(6) colony forming units (cfu) in 2 mu l of PBS and maintained for 24 h. By scanning electron microscopy the percentage of the organ culture surface exhibiting epithelial damage increased from 5.3+/-1.4 in controls to 12.5+/-6.4-26.3+/-9.1 following infection, with no significant difference between parent strains and their derivatives. There was significant bacterial tropism for mucus, and to a lesser extent damaged cells, which was not influenced by the LPS phenotype. All strains caused separation of epithelial cells, adhered to non-luminal cell surfaces, and invaded the epithelium intercellularly. We conclude that Hib associated with mucus and damaged epithelium, and infrequently with normal epithelium, but changes in the LPS phenotype did not affect the interaction between Hib and the mucosal surface of human nasal turbinate tissue. (C) 1996 Academic Press Limited