Phase variation of lic1A, lic2A and lic3A in colonization of the nasopharynx, bloodstream and cerebrospinal fluid by Haemophilus influenzae type b.

The role of phase variation of lic1A, lic2A and lic3A in the ability of Haemophilus influenzae type b to colonize the nasopharynx, bloodstream and cerebrospinal fluid (CSF) of infants was investigated. This was achieved by using PCR to determine the number of 5'-CAAT-3' repeats present in each gene, which is indicative of whether each ORF can be expressed. Multiple PCR products of different intensities were amplified from all three genes at each site sampled. This indicated that the nasopharynx, bloodstream and CSF were colonized by a heterogeneous population of organisms, expressing different combinations of lic genes. At each site however, a predominant PCR product was amplified from each gene, indicating that organisms with this genotype were the most abundant. The number of 5'-CAAT-3' repeats in this predominant product varied depending upon whether organisms were isolated from the nasopharynx, bloodstream or CSF. These observations suggest that the expression of different combinations of lic genes may influence the efficiency with which H. influenzae colonizes the nasopharynx, bloodstream and CSF of infant rats.