Mycoplasmas are the smallest and simplest of the procaryotypes capable of self-reproduction (0.15 to 0.25 μm). They differ from other bacteria in their lack of a cell wall and hence a natural resistance to ß-lactams. Since mycoplasmas are relatively fragile, they will only grow in acellular cultures in the presence of various growth factors and at a constant temperature of 35 to 37 °C.
Most human mycoplasmas are commensal. Of the 9 species that have been isolated from the urogenital tract, Ureaplasma urealyticum and Mycoplasma hominis are the most commonly found. U.u. and M.h. are sexually transmitted and can be pathogenic. Respiratory infections or meningitis can occur in the neonate as a result of contamination from the genital tract at birth. In adults, the infections caused by U.u. and M.h. are described in the table below:
Conventional diagnosis is based upon culture on A7 agar plates followed by microscopical identification of U.u. (sea urchin shaped) or M.h. (fried-egg shaped) colonies.
Since both U.u. and M.h. are commensal, infection can only be diagnosed through the determination of the pathological threshold, followed by precise enumeration.
Given their lack of immunogenicity, serological testing of mycoplasmas does not replace direct diagnosis from patient specimens. The serologic test for urogenital mycoplasmas is especially used to diagnose a deep genital infection, like salpingitis or prostatitis.
The technique of metabolic inhibition using lyophilized reagents and reference strains is the most appropriate technique for use by non-specialized laboratories.