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J Clin Microbiol. 2019 Jun 26. pii: JCM.00344-19. doi: 10.1128/JCM.00344-19. [Epub ahead of print]

Analysis of infection loads in Mycoplasma genitalium clinical specimens using a commercial diagnostic test.

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Centre for Women's Infectious Disease, Royal Women's Hospital, Parkville, Victoria, Australia.
Molecular Microbiology Research Group, Murdoch Children's Research Institute, Parkville, Victoria, Australia.
Department of Obstetrics and Gynaecology, Melbourne University, Parkville, Victoria, Australia.
SpeeDx Pty Ltd, Sydney, Australia.
School of Population and Global Health, University of Melbourne.
Central Clinical School, Monash University, Melbourne, Australia.
Melbourne Sexual Health Centre, Alfred Health, Melbourne, Australia.
Royal Children's Hospital, Parkville, Victoria, Australia.


Mycoplasma genitalium is a common sexually transmitted infection with a propensity to acquire resistance to commonly used antimicrobial therapies. Bacterial load has been linked to patient symptoms and the success of treatment. In this study we demonstrate methodology to estimate load from routine diagnostic assays using the ResistancePlusĀ® MG test (SpeeDx Pty Ltd, Australia). The method gave comparable quantitation to an M. genitalium-specific 16S rRNA qPCR (Spearman r=0.94) for the samples analysed (n=499, including urine and swab types as detailed below), and was therefore employed to analyse typical load levels for samples in a diagnostic laboratory (total of 1012 tests). When stratified by sample type, female urine (median 826 genomes/mL) had the lowest load. This was significantly lower than median loads for all other sample types [male urine (6.91x103 genomes/mL), anal swabs (5.50x103), cervical swabs (8.15x103), endocervical swabs (3.97x103), vaginal swabs (6.95x103)] (p<0.0001). There were no significant differences in load estimates between the other sample types. Reproducibility of load estimates conducted on the same samples was high (r>0.85). In conclusion, this methodology to provide load estimates for M. genitalium can be easily integrated into routine diagnostic laboratory workflow. Given the association between organism load, symptoms and treatment success, load assessment has future diagnostic potential.


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