Genotyping of Tunisian hepatitis B virus isolates based on the sequencing of preS2 and S regions.

The S nucleotide sequences of five hepatitis B virus strains isolated from plasma samples of Tunisian patients with chronic hepatitis B were determined; the preS2 region of three of them were sequenced. According to the comparative analysis of S peptide sequences with the reported sequences in the database bank, the five hepatitis B strains were shown to be related to the D genotypic group, subtype ayw. The nature of residues at positions 125 and 127 allowed us to distinguish between each subtype of the D group and to class all five Tunisian sequences in the 'ayw2' subtype. Moreover, two of them (1366 and 523) contained a substitution of the invariant Cys69 by Arg and Cys221 by Phe, respectively. Potential structural modifications due to the Cys-Arg change are discussed.