Genotype distribution of genital Chlamydia trachomatis in Chiang Mai, Thailand

Urogenital isolates (N=84) of Chlamydia trachomatis collected from high-risk STD subjects in Chiang Mai and the surrounding areas were investigated for genotype distribution. C. trachomatis genotypes were determined by the PCR-based RFLP technique and confirmed by nucleotide sequencing. By this method, the VD4 DNA of the MOMP gene was amplified and digested separately with 4 restriction endonucleases, AluI, HindIII, DdeI, and EcoRII. The nucleotide sequence was determined by dye terminator cycle sequencing. Eight different C. trachomatis genotypes were identified: genotype D (34.5%), F (21.4%), K (13.1%), H/Ia (8.3%), E (7.1%), B/Ba (7.1%), G (6.0%), and J (2.4%). Genotype D and F were the commonest, accounting for 56% of the C. trachomatis infections. When nucleotides of the VD4-MOMP gene were anlyzed, 43 samples (51.2%) had nucleotide sequences that differed from the prototypes, while 41 (48.8%) were identical. Nucleotide substitution mutation was the major mechanism in these variants; changes in nucleotide sequences usually resulted in amino acid substitution, which could lead to a modification of antigenic determinants and the consequent evasion of immune responses.