Sexual mycoplasmas.

Sexual mycoplasmas

Nongonococcal urethritis, the most common sexually transmitted disease in men, is an inflammation of the urethra caused by anything but Gonococcus bacteria. Several microorganisms, including Chlamydia trachomatis and Mycoplasma hominis, can cause it, and now David Taylor-Robinson has a new candidate: Mycoplasma genitalium.

Taylor-Robinson, of the Clinical Research Centre in Harrow, england, and his colleague Joseph G. Tully of the National Institute of Allergy and Infectious Diseases' facility in Frederick, Md., first isolated the microorganism from men with nongonococcal urethritis. In laboratory culture M. genitalium behaves like other disease-causing organisms -- it sticks to red blood cells and bursts them, and also sticks to plastic surfaces.

The researchers have since found antibodies to the microorganism in women with pelvic inflammatory disease, but M. genitalium's role in that disease has yet to be determined. "Antibody response does not equal disease," notes Taylor-Robinson. The organism has also been found in men and women with no symptoms of urogenital infection. This could mean that M. genitalium doesn't itself cause disease, or it could mean that mycoplasma strains differ from one another in virulence, he suggests.

The next step in studying an organism's infectivity is to incoulate with it. "The best animal model by far is the human," Taylor-Robinson says. Because few people are likely to volunteer, he and his colleagues resorted to various monkey species and mice and hamsters to determine whether the microbe can cause infection. While the mice, the hamsters and some of the monkeys were resistant, other primates, including chimpanzees, became infected. This suggests, says Taylor-Robinson, that M. genitalium may play a role in human genital tract infections.

The present detection tool -- culturing for the organism -- can take a month or so to demonstrate the presence of M. genitalium. With gene probes and monoclonal antibodies introduced at the meeting, the process would take only a few hours. These tools may bring M. genitalium's role into the light, Taylor-Robinson says.