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18 Sep 2018

Mycoplasma genitalium - a challenging STI

Mycoplasma genitalium is a relatively newly discovered bacterium, having first been identified in 1980 [1].  

Vesna De Petra, Microbiological Diagnostic Unit Public Health Laboratory, the University of Melbourne, at the Doherty Institute and Catriona Bradshaw, Melbourne Sexual Health Centre

It is sexually transmitted and is a cause of urethritis in men, cervicitis and pelvic inflammatory disease in women, and rectal infection in both genders. A recent meta-analysis found M. genitalium also increases the risk of preterm delivery and spontaneous abortion [2].

M. genitalium is a parasitic bacterium with the smallest known genome of any free living bacteria. Mycoplasmas are believed to have evolved from gram-positive bacteria through a process of gene deletion [3]M. genitalium lacks a cells wall which prevents detection by staining, but also means antimicrobials that act on the cell wall such as beta-lactams are ineffective. Due to the fastidious requirements for culturing the organism and its slow growing nature (2-3 months to culture), nucleic acid amplification tests (NAATs) are used for diagnosis. However, NAAT testing has only recently become commercially available. 

Testing for M. genitalium is currently indicated in individuals with urethritis, cervicitis, pelvic inflammatory disease, proctitis, and current partners of patients infected with M. genitalium (even if asymptomatic), to prevent potential reinfection [4]. Asymptomatic screening is not recommended, in part because of the challenges emerging regarding treatment.

What makes M. genitalium so challenging to manage is its limited susceptibility to available classes of antimicrobials and the emergence of multidrug resistance. The only classes with activity against M. genitalium include macrolides, fluroketolides, streptrogramins and fourth generation/extended spectrum quinolones [5]. Emergence of resistance to macrolides, the first line therapy for M. genitalium, has occurred over the last decade, with fewer than 10% of strains displaying resistance in 2006, to over 60% of strains being macrolide resistant in 2016, increasing to over 80% in men who have sex with men [6,7]. Quinolone resistance has also emerged, particularly in the Asia-Pacific region, impacting on the efficacy of moxifloxacin which is recommended for macrolide resistant strains [8]. Resistance guided therapy is a new but essential approach to effective treatment and control of M. genitalium, as highlighted in a recent study conducted at the Melbourne Sexual Health Centre (MSHC) [9].

The extraordinarily rapid emergence of antimicrobial resistance, coupled with intrinsic resistance to readily available antimicrobials, means M. genitalium, especially in the Asia-Pacific region, might become the first untreatable STI.

[7] Unpublished reference: Read TRH, Murray GL, Danielewski J, Fairley CK, Doyle M, Jensen JS, Worthington K, Su J, Mokany E, Tan L, Lee D, Vodstrcil LA, Chow EPF, Garland SM, Chen M Bradshaw CS. Symptoms, sites and significance: Mycoplasma genitalium in men who have sex with men. (Under review, Emerging Infectious Diseases)

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