Variability of theChlamydia trachomatis omp1Gene Detected in Samples from Men Tested in Male-Only Saunas in Melbourne, Australia

Abstract

C. trachomatis serovars can be differentiated by sequencing the omp1 gene, which codes for the major outer membrane protein (MOMP) (1, 5, 8, 15-17, 25, 31). Preliminary evidence suggests that MOMP is a porin that assembles as ␤ barrels containing conserved domains (CDs) of transmembrane ␤ strands and periplasmic loops and four variable domains (VDs) located on the outer loops (14, 28). Serovars exhibit MOMP sequence heterogeneity that is mainly localized to the VDs (27, 36). Variability in the MOMP sequence is presumably a result of host selection and bacterial adaptation (3,4,19), although recent analysis of nucleotide and amino acid substitutions for omp1 and MOMP, respectively, showed a lack of evolutionary pattern with respect to disease or tissue tropism (29). The findings from studies of the clinical manifestations of disease and the association of those manifestations with specific serovars (2,7,12,17,23,26,34), geographic clustering (5, 8, 11), and the amount of variation within genotypes and the changes in the frequencies of the genotypes circulating over time (16,17,25,30,35) have been mixed. Other studies have highlighted the importance of MOMP diversity in strains isolated from sex workers, whose sexual network was described as a core group creating selective immune pressure on circulating strains (3, 4). Overall, of the serovars usually associated with urogenital infection (serovars D to K), serovars D, E, and F are the most common (1,5,8,11,12,15,17,23,30,31).The aims of the present study were to characterize the C. trachomatis strains detected in samples collected during a sauna screening program (20) by sequencing the omp1 gene and determining the corresponding serovars. Determination of the serovars and the omp1 variability of the C. trachomatis strains detected in these samples may give insight into the C. trachomatis strains circulating among MSM who frequent saunas. MATERIALS AND METHODSClinical samples. A sample of 47 C. trachomatis-positive specimens collected from 39 men who participated in a screening program in male-only saunas in Melbourne, Victoria, Australia (20), was used. These 47 samples comprised 34 anal swab specimens, 10 urine samples, and 3 throat swab specimens. Two anal swab specimens were collected from each of five men, and two urine samples were collected from each of two men; i.e., the samples were collected at the initial consultation in the sauna and repeat samples were then collected (for confirmation before antibiotic treatment). C. trachomatis was detected at two anatomical sites in one man: from an anal swab specimen and a urine sample.Isolation of DNA and omp1-specific PCR. DNA extraction and omp1-specific PCR were performed as described previously (20,21). Three omp1-specific PCRs were used: PCR VD1-4 with primers P1 and OMP2 to amplify a region of the gene containing all four variable domains (17), nested PCR VD1/2 with primers P1 and CT6 (5) to amplify a region containing VD1 and VD2, and nested PCR VD3/4 with primers CT6 (sense) and OMP2 to amplify a region con...

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