Spotlight 16/07/2018 ‘It’s coming home’

Recently there has been an increase in interest in a ‘new’ STI that is being hyped as the next new ‘superbug. We have known about Mycoplasma genitalium (aka MG or MGen) since 1980[2] when it was identified at St Mary’s Hospital.  Mgen can cause urethritis (swelling and irritation of the urethra) in men, and has been linked to cervicitis (inflammation of the cervix), pelvic inflammatory disease, and possibly infertility in women. However currently there is little public knowledge despite in some populations it is more common than gonorrhoea. Routine testing is not currently recommended which then disincentives commercial development of diagnostics so there are very few commercial diagnostic kits for Mgen, although it can be picked up by PCR, making diagnosis a problem. The effect is that incidence of infection is a relative unknown but some small studies have found it in be as common as 14.7% in men[3].

Mgen has many features that make it an interesting bug in it’s own right. Firstly being a mycoplasma means it has no cell wall so antibiotics targeting that don’t work making it intrinsically resistant to beta-lactams, glycopeptides and fosfomycin and a mutation in ropB renders it non-susceptible to rifampicin. Lacking a cell wall is potentially a result of an ancestral bacteria opting for an obligate parasitical lifestyle which has the added effect of making growing the bacteria in research and diagnostic laboratories extremely difficult – this is obviously a problem if you are trying to calculate MIC values. Treatment is usually with the macrolide Azithromycin but there has been evidence of treatment failure globally for several years. While a second line antibiotic, Moxifloxacin, can be used there a reports of resistance emerging to this as well. Hence a new ‘superbug.

Mgen parasitic lifestyle allows for a very small genome; only roughly 500 genes compared to S. aureus ~2700 and B. pseudomallei ~5,600. Due to the small size of the Mycoplasma genome a close relative (Mycoplasma mycoides) was the bacteria completely synthesised from DNA by J. Craig Venter and the basis for the minimal genome project.

Mgen is currently a treatable disease but lack of diagnostics, informed treatment and misuse of Azithromycin could again lead to emergence of another untreatable STI.

 

[1] Emerging sex disease MG ‘could become next superbug’ https://www.bbc.co.uk/news/health-44777938

[2] Mycoplasma genitalium – History https://en.wikipedia.org/wiki/Mycoplasma_genitalium#History

[3] High Prevalence of Antibiotic-Resistant Mycoplasma genitalium in Nongonococcal Urethritis: The Need for Routine Testing and the Inadequacy of Current Treatment Options https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3922211/

[4] Researchers start up cell with synthetic genome https://www.nature.com/news/2010/100520/full/news.2010.253.html

 

By Richard Stabler, AMR Centre Co-Director.

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