Polymerase chain reaction (PCR) has stamped "solved" on adecade-old search for the perpetrator of non-gonococcalurethritis (NGU). Once a urologist has ruled out Neisseriagonorrhoeae as causing the genital symptoms, about half of hispatients are diagnosed with NGU, for which the etiology isuncertain.
Chlamydia trachomatis is commonly considered the guiltyparty in NGU, but another microbial suspect, Mycoplasmagenitalium, was accused in Lancet 12 years ago. It reportedthat this microorganism, recovered from the urethral dischargeof two British men, had been cultured and identified by JosephTully of the National Institute of Allergy and InfectiousDiseases (NIAID) and David Taylor-Robinson of St. Mary'sHospital, London.
Tully, who now heads NIAID's mycoplasma laboratory sectionin Frederick, Md., recalled to BioWorld that in the summer of1980, Taylor-Robinson brought to NIH from London frozenurethral-discharge samples, which they put in prolongedincubation.
"In those days," Tully said, "about half of all NGU cases wereattributed to C. trachomatis, perhaps 10 or 15 percent toUreaplasma urealyticum (a more readily recognized taxonomiccousin of mycoplasma), and for as much as 30 or 40 percent, nobacterial agent could be identified. Many were treated blind bytetracycline, and their infections resolved."
When he and Taylor-Robinson isolated M. genitalium (whichthey named), they thought, "This may be the organism fillingthat void."
In the years since then, growing and recognizing M. genitaliumin venereal disease clinics has proven so laborious and trickythat for all practical purposes, C. trachomatis remains thealleged pathogen of choice.
But when PCR came on the scene, Taylor-Robinson, who headsthe Division of Sexually Transmitted Diseases in the ClinicalResearch Center at Harrow, England, knew his hour had struck.
It struck as well for J. S. Jensen at Denmark's State SerumInstitute in Copenhagen. Each separately developed a PCRreaction for M. genitalium. Taylor-Robinson's can detect 10-15grams of the microbe's DNA, equivalent to about 10 organisms.
In last Saturday's Lancet, he and his colleagues report theirfindings on "Association of Mycoplasma genitalium with acutenon-gonococcal urethritis."
"The problem with M. genitalium was that it was alwaysextraordinarily difficult to culture," Taylor-Robinson toldBioWorld. "Only because of the new molecular techniques havewe been able to do any sensible work on it. Only a specificpolymerase chain reaction made it possible to detect theorganism much more easily."
At St. Mary's Hospital, his group collected urethral-dischargeand urine samples from 103 men with symptoms and/or signsof acute NGU, and from 53 control patients. PCR spotted themycoplasma in 24 percent of the 103, but in only three (6percent) of the controls.
This association was independent of age, ethnic origin, lifetimenumber of sexual partners and recent change of partner. Itdetected M. genitalium in almost 30 percent of cases without C.trachomatis. The findings "suggested that the mycoplasmaoccurred more frequently in the urethras of men with NGUthan in men with gonorrhea or without urethritis."
A course of antibiotic, usually tetracycline, quickly clears upmost cases of NGU, perhaps too quickly.
Taylor-Robinson said that a colleague, Philip Hay, now at St.George's Hospital, London, has recently found that in his specialclinic for recurring and chronic NGU, M. genitalium showed upin 20 percent. "When treated with a prolonged course oferythromycin, six weeks, a good proportion of the patientsrecovered and became PCR-negative for mycoplasma."
If his PCR findings can be validated, Taylor-Robinson added, "itmay change clinical practice in relation to chronic disease.People should be treated much much longer."
Almost as he spoke, Jensen's group in Copenhagen, with its ownPCR probes, had just confirmed the London group's indictmentof M. genitalium in NGU.
Mycoplasma are the smallest known bacterial organism thatcan grow in laboratory culture media. Some are only 0.2microns in diameter. Clinically, the organism's commonestmanifestations are atypical pneumonia and respiratoryinfection, the work of M. pneumoniae., often mixed, said Tully,with M. genitalium
Researchers and pathologists live in constant dread ofmycoplasma contaminating their cultures. When this happens,one remedy, often quoted dead-pan, is to "burn down your laband build somewhere else. That's not crazy," said Taylor-Robinson.
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.