Sequence-based typing of Mycoplasma genitalium reveals sexual transmission

Abstract

Mycoplasma genitalium causes male nonchlamydial, nongonococcal urethritis and is associated with cervicitis and pelvic inflammatory disease in women. Epidemiological studies indicate that M. genitalium is sexually transmitted, and the aim of the present study was to further substantiate this by means of a DNA typing system. A typing assay based on a diagnostic mgpB gene PCR was developed, evaluated, and applied directly to urogenital specimens. The assay had a low limit of detection and hence a high typeability. Sequences of isolates from 52 unrelated patients were divided into 29 different sequence types, giving a discriminatory index of 0.95. Two to six M. genitalium-positive specimens were collected from each of 44 patients over a median interval of 56 days (range, 11 to 1,395). Forty had the same sequence type in consecutive specimens. Specimens collected from two men were repeatedly positive at intervals of 472 and 1,395 days, respectively, but the sequence types had changed. A new strain was introduced in one sexual dyad, and the sequence types changed subsequently. Seventy-nine M. genitalium-positive specimens from 19 couples were investigated, and all partners initially had concordant sequence types, but one couple had discordant types at one time point before a newly introduced strain took over. The present typing system is simple and reproducible and has an excellent discriminatory capacity which might prove useful in studies of sexual networks and for evaluation of treatment failures. In the laboratory, this system may document the uniqueness of newly isolated M. genitalium strains.

FIG. 1.

Dendrogram showing clustering of 52 DNA sequences acquired from urogenital specimens and M. genitalium strains obtained from patients with no known sexual relationship.

FIG. 2.

Dendrogram showing clustering of 65 specimens from 18 M. genitalium-positive couples. Some patients provided specimens from several anatomical sites and/or on more than one occasion. The presence of the same sequence at several time points in the cluster demonstrates the stability of the typing system. The gray shading and the symbols to the left of the specimen numbers show specimens belonging to the same couple in sequence type clusters comprising more than one couple. Note that all sequences within couples are the same. Each specimen is listed with its laboratory specimen number, with couples identified by the letters A through S and each letter followed by a two-digit number, with the first digit indicating sex (1, male; 2, female) and the second digit indicating the sequence of the specimen. Thus, 11 denotes the first specimen from the male partner and 23 the third specimen from the female partner.