Analysis Identifying Common and Distinct Sequences among Texas Clinical Strains of Mycoplasma genitalium

Mycoplasma genitalium is a human bacterial pathogen linked to urethritis and other sexually transmitted diseases. Here, we assessed the incidence of M. genitalium infection in patients attending a sexually transmitted disease clinic in San Antonio, TX, by use of diagnostic real-time PCR. Overall, 16.8% of women and 15.1% of men were found M. genitalium positive. Regions of the mgpB gene, which encodes the MgPa adhesin, were amplified from positive clinical specimens and evaluated for sequence variability, which demonstrated transmission of the pathogen between sexual partners. Follow-up analysis of a subset of patient specimens revealed reinfection by a different strain of M. genitalium, indicating the absence of protective immunity. Eighteen DNA sequence variants were obtained and compared with all other available clinical sequences. Detailed analysis revealed silent mutations of six amino acid residues within the encoded region of the MgPa adhesin in numerous clinical strains. In addition, missense mutations of limited numbers of amino acids were observed. Alignment of putative amino acid sequences revealed the simultaneous occurrence of several mutations and the existence of identical or similar protein variants in strains from different locations.Mycoplasma genitalium is associated with numerous human genitourinary tract maladies, including nonchlamydial, nongonococcal urethritis in men and cervicitis, endometritis, and pelvic inflammatory disease in women (1, 4, 5, 12, 19, 29, 30, 35, 39). Understanding the epidemiological aspects of infections and developing effective treatment require reliable typing of pathogenic microorganisms. Since M. genitalium is very difficult to culture from clinical specimens (13, 21), classical microbiological typing methods are not readily applicable. Furthermore, serological approaches are not widely used because of cross-reactivity with other mycoplasmas, especially with Mycoplasma pneumoniae (15, 26). Therefore, typing of M. genitalium strains relies on DNA sequence data. Recently, sequence variability of the rRNA operon and tandem repeats in the MG309 locus have been evaluated with clinical specimens (28). However, the majority of M. genitalium clinical sequence data available today is based upon the gene mgpB (locus MG191 of sequenced reference strain G37 11]) encoding the M. genitalium adhesin MgPa (14, 17, 21). An M. genitalium-specific diagnostic PCR assay was designed to target the proximal unique region of this gene (using primers MgPa-1 and MgPa-3 22] and designated here “MgPa-13”). The MgPa-13 region has exhibited sequence stability in persistently infected patients for up to 21 months (17). Despite this intrastrain stability, high levels of sequence variability between clinical isolates were observed (14, 17). Based on this sequence region, transmission of M. genitalium between sexual partners was shown, as was colonization of different anatomical sites of the same patient by identical strains (14).Here, we present analysis of MgPa-13 sequences generated from clinical specimens collected at the Project S.A.F.E. sexually transmitted disease (STD) clinic in San Antonio, TX (36), from recruited female participants and their male partners. Alignment of MgPa-13 sequences corroborated transmission between partners and colonization of different anatomical sites by the same strain. Comparison of newly recovered sequences with all currently available clinical data (14, 17, 21) revealed not only the presence of several common variants but also distinct sequences. Analyses of encoded amino acids uncovered mutations that determine common features among MgPa-13 region variants.