Literature review > Issue 8 > Review on Jensen et al. 

Jensen and colleagues present a well-designed and thoughtful study assessing the correlation between the quantity of M. genitalium in patient specimens with signs and symptoms of urethritis in men. Using either urine or urethral specimens, there was a correlation between the quantity of M. genitalium genomes and disease severity assessed by the quantity of urethral inflammatory cells and urethral discharge. These findings, along with the many clinical studies showing the correlation of M. genitalium with urethritis, further support the etiologic role of M. genitalium with this disease syndrome. In addition, this PCR assay is sensitive and specific, not subject to inhibition under the conditions used, and thus should be useful to other researchers studying this emerging pathogen.

The authors of the current paper should be complemented for providing so many details of technical features that affect the detection of M. genitalium in patient specimens. Particularly useful are the procedures used for validation of their newly developed quantitative PCR assay by its concordance with an independent PCR assay. Also informative are the clear presentation of the reproducibility of the assay, the well documented limit of detection, and the effect of patient specimen material on the limit of detection and reproducibility of the assay. Similar documentation of future assays, particularly those in which culture and PCR results do not correlate [1], would be useful for the interpretation of the clinical studies in which these assays are applied.

The relative organism load and limit of detection in urethral and urine specimens deserves comment. In the current study, detection in urine was more sensitive than detection in urethral specimens, a finding that is specific to the sample preparation procedures used. For example, after processing, a sample volume equivalent to 2 μl of 1800 μl urethral specimen was used in the PCR assay in contrast to a sample equivalent to 36 μl of the 15-20 ml urine specimen. Different sample preparation procedures allowing the addition of different amounts of specimen would alter the relative sensitivity of detection in these two specimen types in men. However, the good sensitivity in urine specimens and the ease of collection of this noninvasive specimen type makes this the specimen of choice for screening men for this urethral pathogen using the techniques outlined in this study.

The extensive strain typing analysis of M. genitalium indicates that the sequences from infecting M. genitalium can be clearly differentiated from each other and from G-37, the type strain for this species. This system is easily applied to both isolated strains of this organism and to M. genitalium sequences within patient specimens because it is based on sequence polymorphisms within the PCR product generated from the standard diagnostic PCR test for this organism. Many of the strain types identified in this study were also detected in our studies based in Kenya (unpublished), further attesting to the stability of these sequence polymorphisms among strains. In contrast to the sequence heterogeneity among the M. genitalium strains identified in this and several studies [2-4] including our own (unpublished), isolates of M. genitalium archived in ATCC are identical by several strain typing methods [2-4], indicating either that the ATCC strains are culture contaminants of G37 or that the culture techniques used by others do not isolate all strains of this organism. In either case, researchers should be aware of the clonality of the archived ATCC strains when assessing phenotypic diversity, such as antibiotic susceptibility, among this species.

References

1. Baseman, J. B., M. Cagle, J. E. Korte, C. Herrera, W. G. Rasmussen, J. G. Baseman, R. Shain, and J. M. Piper. 2004. Diagnostic assessment of Mycoplasma genitalium in culture-positive women. J Clin Microbiol 42:203-11.

2. Jensen, J. S., E. Bjornelius, B. Dohn, and P. Lidbrink. 2004. Use of TaqMan 5' nuclease real-time PCR for quantitative detection of Mycoplasma genitalium DNA in males with and without urethritis who were attendees at a sexually transmitted disease clinic. J Clin Microbiol 42:683-92.

3. Kokotovic, B., N. F. Friis, J. S. Jensen, and P. Ahrens. 1999. Amplified-fragment length polymorphism fingerprinting of Mycoplasma species. J Clin Microbiol 37:3300-7.

4. Ma, L., and D. H. Martin. 2004. Single-nucleotide polymorphisms in the rRNA operon and variable numbers of tandem repeats in the lipoprotein gene among Mycoplasma genitalium strains from clinical specimens. J Clin Microbiol 42:4876-8.

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