CHLAMYDIA-TRACHOMATIS FROM INDIVIDUALS IN A SEXUALLY-TRANSMITTED DISEASE CORE GROUP EXHIBIT FREQUENT SEQUENCE VARIATION IN THE MAJOR OUTER-MEMBRANE PROTEIN (OMP1) GENE

60 cervical Chlamydia trachomatis infections identified by antigen det ection from 51 prostitute women in Nairobi, Kenya were evaluated for s equence polymorphism in the major outer membrane protein (omp1) gene. DNA from clinical specimens was amplified by the polymerase chain reac tion and cycle sequenced through variable domains (VD) 1, 2, and 4. 37 (63%) samples had variant VD sequences, 19 (32%) samples had prototyp e VD sequences, and 4 (6%) samples contained omp1 sequences from two o r more C. trachomatis strains. Among the 37 variant strains, 18 had tw o or fewer nucleotide substitutions in one or two VDs and represented point mutational drift variants. 19 strains had a larger number of nuc leotide changes and displayed mosaic omp1 sequences that may have been generated by omp1 VD recombination. We conclude that the prevalence o f C. trachomatis omp1 DNA polymorphism is substantial among prostitute women in Nairobi, Kenya and that this is the likely result of immune selection pressure.