Abstract: Objective To develop a reverse dot blot (RDB) technology for detecting and genotyping of urogenital Chlamydia trachomatis.Methods The oligonucleotide probes were designed by using a software (Oligo).The VS1-VS2 of C.trachomatis ompl gene was amplified by a nested PCR and then the labeled amplicons were hybridized with serotype-and group-specific oligonucleotide probes for the propose of detection and genotyping.Results The concordance rate was 98.2% (56/57) when the sensitivities of nest VS1-VS2 PCR and plasmid PCR were compared in 60 clinical samples.Eleven serotype-specific probes (A,B+Ba,C,D,E,F,G,H,I,J and K) and 3 group-specific probes ( group B ( B,Ba,D and E),group C (A,C,H,I,J and K) and intermediate group (F and G)),targeting the VS1-VS2 region of ompl gene of 11 different serovars of C.trachomatis,were optimized by the Nucleotide-nucleotide Blast (blastn) program and different reaction conditions.The probes were shown to have specific reactions with the corresponding reference strains.The 56 positive samples detected by the nested PCR all showed positive hybridization by RDB method.A total of 59 strains of C.trachomatis were identified.They included eight genotypes,and types E,F,D and H were the most common (77.9%).Multiple infections with serovars D/E,D/F,F/K,were found in 3 cases (5.4%),respectively.Conclusions RDB technology can directly detect and genotype C.trachomatis from clinical samples.It is simple,rapid and specific,and is useful for large epidemiological studies and for differentiating clinical re-infection from mixed infection.

Key words: Chlamydia trachomatis, Genotype, Oligonucleotide probes