VARIATION OUTSIDE VARIABLE SEGMENTS OF THE MAJOR OUTER-MEMBRANE PROTEIN DISTINGUISHES TRACHOMA FROM UROGENITAL ISOLATES OF THE SAME SEROVAROF CHLAMYDIA-TRACHOMATIS

Objectives-Whereas serovars A, B, Ba and C of Chlamydia trachomatis ar e usually associated with trachoma, two of these serovars (Ba and C) a re occasionally observed in urogenital infections. Variation in the ge ne encoding the major outer membrane protein (MOMP) was explored to di stinguish urogenital from trachoma specimens of the same serovar. Meth ods-A large portion of the MOMP gene was amplified by nested PCR direc tly from clinical samples from trachoma or urogenital infection and th e serovar of the infecting C trachomatis was determined by restriction fragment length polymorphism (RFLP). Amplified DNA from trachoma sero vars B, Ba and C and from urogenital serovars Ba, C, D and E was seque nced by the dideoxy chain termination method. Results-While almost ide ntical in variable segment (VS)I, three urogenital Ba samples differed from all trachoma B and Ba samples at eight nucleotides including two sites which changed amino acids in the constant region upstream of VS I. An identical sequence in this region was observed for the reference urogenital D serovar. Variation in this same region upstream of VSI a lso distinguished 40% of serovar D samples from prototype D including three that were sequenced. Two urogenital C differed from trachoma C s amples at four sites that changed the MOMP amino acid sequence includi ng two changes in the constant region between VSII and III and single changes in VSII and III. On the basis of these sequence determinations , RFLP was pre-dieted which allowed extension of these observations to 20 other urogenital Ba, 12 trachoma B or Ba, seven variant D, 12 D, f our urogenital C and three trachoma C samples without further sequenci ng. Conclusion-Urogenital Ba and C samples have VSI or II and III sequ ences identical or very similar to trachoma strains of the same serova r, but resemble more closely other serovars in the constant regions. U rogenital serovar D samples can also be divided into two genotypes on the basis of sequence differences in the constant region preceding VSI .