Mycoplasma genitalium: Accurate Diagnosis Is Necessary for Adequate Treatment

Abstract

Background: Mycoplasma genitalium is very difficult to grow in culture but has been more able to be studied for disease associations since the advent of research molecular amplification assays. Polymerase chain reaction (PCR) and other molecular assays have demonstrated an association with adverse disease outcomes, such as urethritis or nongonococcal urethritis in men and adverse reproductive sequelae in women-for example, cervicitis, endometritis, and pelvic inflammatory disease (PID), including an association with risk for human immunodeficiency virus. The lack of commercially available diagnostic assays has limited widespread routine testing. Increasing reports of high rates of resistance to azithromycin detected in research studies have heightened the need available commercial diagnostic assays as well as standardized methods for detecting resistance markers. This review covers available molecular methods for the diagnosis of M. genitalium and assays to predict the antibiotic susceptibility to azithromycin.

Methods: A PubMed (US National Library of Medicine and National Institutes of Health) search was conducted for literature published between 2000 and 2016, using the search terms Mycoplasma genitalium, M. genitalium, diagnosis, and detection.

Results: Early PCR diagnostic tests focused on the MPa adhesion gene and the 16S ribosomal RNA gene. Subsequently, a transcription-mediated amplification assay targeting ribosomes was developed and widely used to study the epidemiology of M. genitalium. Newer methods have proliferated and include quantitative PCR for organism load, AmpliSens PCR, PCR for the pdhD gene, a PCR-based microarray for multiple sexually transmitted infections, and multiplex PCRs. None yet are cleared by the Food and Drug Administration in the United States, although several assays are CE marked in Europe. As well, many research assays, including PCR, gene sequencing, and melt curve analysis, have been developed to detect the 23S ribosomal RNA gene mutations that confer resistance to azithromycin. One recently developed assay can test for both M. genitalium and azithromycin resistance mutations at the same time.

Conclusions: It is recommended that more commercial assays to both diagnose this organism and guide treatment choices should be developed and made available through regulatory approval. Research is needed to establish the cost-effectiveness of routine M. genitalium testing in symptomatic patients and screening in all individuals at high risk of acquiring and transmitting sexually transmitted infections.

Keywords: Diagnostic tests; Mycoplasma genitalium; azithromycin resistance; macrolide resistance.

Figure 1.

PlexPrimers are combined with PlexZymes for mutation-specific amplification and detection with quantitative polymerase chain reaction (qPCR). The PlexPrimer contains 3 sections; a long 5’ target-recognition sequence (5T), a short 3’ target-specific region (3T) matched to the mutation sequence (M) and an intervening insert sequence (INS), which does not bind to the target rather increases the specificity of the 3T region for the mutant over the wild type sequence. During amplification, the INS is incorporated into the PlexPrimer amplicons, and these can be detected in real time using PlexZymes, nucleic acid enzymes that form, from their component partzymes (A and B), only when matched PlexPrimer amplicons are present. Each partzyme contains a probe-binding arm, a partial catalytic core, and a target-binding arm, oriented such that partzyme A binds to the amplicon in the region containing the INS, and partzyme B binds adjacently downstream. Catalytically active PlexZymes bind and cleave reporter probes separating a fluorophore (F) and quencher (Q), resulting in signal generation.