Literature review > Issue_3 > Review Mena et al. 

Recent interest in the disease associations of M. genitalium have generated a plethora of articles describing the association of this organism with reproductive tract disease in both men and women. To date, 14 of 15 studies have shown an association of this organism with urethritis, NGU, and/or nonchlamydial NGU in men, despite differences in study design, populations studied, and PCR assays utilized. The consistency of these studies as well as the ability of this organism to elicit genital tract disease in primate models, suggests that M. genitalium is the causative agent in previously idiopathic cases of urethritis in men. Fewer studies have assessed the association of M. genitalium with disease in women, although several researchers have reported an association with cervicitis, endometritis, and pelvic inflammatory disease.

In the current report, Mena et al. analyzed the association of M. genitalium with acute urethritis in yet another population, African American men the Southern United States. Unlike most previous studies, there was a high coinfection rate of M. genitalium with C. trachomatis and N. gonorrhoeae, perhaps reflecting differences in the epidemiology of this organism among different populations. The authors also noted a lower amount of M. genitalium PCR product generated in their PCR reaction among samples from men co-infected with N. gonorrhoeae, implying that lower amounts of M. genitalium were present in these specimens. Similar results were obtained by Yoshido et al. [1], who used quantitative PCR to show a lower M. genitalium load among men infected with N. gonorrhoeae. These findings suggest that some aspect of N. gonorrhoeae infection, perhaps the greater inflammatory response, inhibits the growth or survival of M. genitalium, and certainly merits further study.

The Mena study presents a previously unpublished PCR tests for M. genitalium, which, similar to most other PCR tests for this organism, targets the MgPa adhesion gene. However, this assay is unique in that it targets a 495 bp sequence initiating 85 bp upstream of the MgPa translational start, a sequence that has not been evaluated for its conservation between strains, nor for its specificity for M. genitalium. While the sensitivity and specificity of this PCR could be questioned, a subsequent report by this group documented the high concordancy of this assay with the newly developed Gen-Probe TMA assay for M.genitalium [2], consistent with its ability to detect M. genitalium-specific sequences in patient specimens. The PCR assay presented in this study adds to our arsenal of unique PCR assays, including those that target the 16S rDNA gene, that can be used to assess the accuracy of detection of this organism in different sample types from different populations.

The ability to use urine, rather than urethral specimens, for detection of M. genitalium would greatly increase patient compliance for testing. Comparisons of the suitability of these two specimen types for detection of M. genitalium are needed. The concordancy of urine and urethral specimens for detection of M. genitalium by PCR (18, 3, and 2 men were positive in both specimens, urethral specimens only, and urine specimens only, respectively, in the current study) adds to our confidence of using urine specimens for screening for this organism. Several previous studies have used urine specimens for detection of M. genitalium and this study, as well as a previous report by Jensen et al. [3], supports the high concordancy of these two specimen types, therefore the use of urine specimens for detection of M. genitalium. Even so, further studies are needed to assess the performance of these different sample types among men without overt disease and among PCR assays using the different specimen preparation methods, which differ in purity and concentration of the target DNA in these two specimen types.

In their study, Mena et al. required that all positive specimens be confirmed by a second identical PCR assay upon repeat from a fresh aliquot of the specimen, a conservative strategy used to control for DNA contamination. The authors noted that specimens that did not repeat typically had barely detectable PCR products in the first PCR assay, a finding that may also be due to a lower organism load in the patient specimen. I support this conservative strategy of interpretation of results because we too have found that DNA contamination is more likely to occur in the sample preparation procedure than the PCR reaction per se and usually results in low amounts of detectable PCR products. Future comparisons are needed to evaluate the sensitivity and specificity of the different M. genitalium assays, different methods of sample preparation, and the use of the conservative repeat strategy for interpretation of results. Such studies will enhance our ability to accurately detect M. genitalium in patient specimens and to evaluate the disease associations and epidemiology of this interesting organism.

References
1. Yoshida T, Deguchi T, Ito M, Maeda S, Tamaki M, Ishiko H. Quantitative detection of Mycoplasma genitalium from first-pass urine of men with urethritis and asymptomatic men by real-time PCR. J Clin Microbiol 2002; 40:1451-5.

2. Martin d, Shaw J, Mroczkowski T, et al. A transcription-mediated amplificaiton (TMA) assay for the detection of Mycoplasma genitalium (Mg) in clinical specimens, 15th Biennial Congress of the International Society for Sexually Transmitted Diseases Research (ISSTDR), Ottawa, Canada, 2003.

3. Jensen j, B Dohn, E Bjornelius, and P Lidbrink. Is urine a suitable specimen type for detection of Mycoplasma genitalium by PCR?, 13th International Organization of Mycoplasma Congress, Fukuoka, Japan, 2000. Abstract #P-L09., 2000.

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