Mycoplasmas are the smallest prokaryotes capable of self replication. Mycoplasma genitalium, one of 14 mycoplasmas of human origin known so far, was isolated originally from the urethra of two of 13 men with non-gonococcal urethritis (NGU) attending the genitourinary medicine (GUM) clinic at St Mary's Hospital, Paddington, London, in 1980.^{1, 2} By electron microscopy, it was found to be flask shaped, the narrow terminal portion being instrumental in its attachment to eukaryotic cell surfaces.^{1, 2} Later, the genome of M genitalium, the smallest known for a self replicating micro-organism, 580 kb, was the first of any micro-organism to be fully sequenced.³ The small genome size probably accounts, as least in part, for the fastidious growth requirements of M genitalium. Indeed, despite the original success of isolating this mycoplasma from the urogenital tract and the subsequent recovery of five strains from the respiratory tract,⁴ further attempts to isolate it from the urogenital tract failed and it was not until the application of a molecular approach that progress was made. It was the advent of polymerase chain reaction (PCR) technology in the late 1980s that saw the development of sensitive and specific PCR assays for M genitalium, initially by two groups of workers and later by others, each group amplifying different fragments of the attachment protein designated MgPa.⁵ This has enabled M genitalium to be detected reliably in urogenital specimens.

In the past 20 years there have been 19 studies,^{1, 6–23} undertaken largely in men attending GUM clinics, in 17 of which the relation of the mycoplasma …