Macrolide resistance--associated 23S rRNA mutation in mycoplasma genitalium, Japan.
This retrospective study was approved by the Institutional Review Board of the Graduate School of Medicine, Gifu University, Gifu, Japan. We collected pretreatment urine specimens from 308 men with NGU who had visited a urologic clinic (iClinic) in Sendai, Japan, during 2006 through 2008 and stored the specimens at -70[degrees]C. Each man gave informed consent. Twenty-five of 58 urine specimens confirmed to be positive for M. genitalium by PCR-based assay were randomly chosen for this study and subjected to DNA purification. The 23S rRNA gene and the ribosomal proteins genes L4 and L22 of M. genitalium were amplified from the purified DNA by PCR as reported previously and then sequenced (5).
In 1 specimen, we found an A-to-G transition at nucleotide position 2072 in the 23S rRNA gene of M. genitalium, corresponding to position 2059 in Escherichia coli (Table). An A2059 (E. coli numbering) residue in region V of the 23S rRNA gene is critical for the binding of macrolides (9) . Mutations of A2058, A2059, and other 23S rRNA residues within the macrolide-binding site can confer a high-level resistance to macrolides in several bacterial species, including M. genitalium (5,9). Therefore, M. genitalium strains that harbor the A2059G (E. coli numbering) mutation in the 23S rRNA gene could be highly macrolide resistant. We also found a T-to-G transition at nucleotide position 2199 in the 23S rRNA gene of M. genitalium, corresponding to position 2185 in E. coli, in 3 specimens, but this mutation has not been associated with macrolide resistance in other bacterial species (9).
We found amino acid changes in L4 and L22 ribosomal proteins in M. genitalium in 9 specimens. L4 and L22 ribosomal proteins each have extended loops, which converge to form a narrowing in the exit tunnel adjacent to the macrolide-binding site (10). Therefore, macrolide resistance--associated missense mutations in L4 and L22 tend to be localized to Gln62-Gly66 in L4 and Arg88-Ala93 in L22 of E. coli, which are closest to the macrolide-binding site (10). All of the amino acid changes in L4 of M. genitalium found in this study corresponded to those at the downstream regions from Gln62Gly66 in L4 of E. coli. Of the amino acid changes in L22 of M. genitalium, the only Gly93Glu change found in M. genitalium harboring the A2059G (E. coli numbering) mutation in the 23S rRNA gene was located within the region corresponding to Arg88Ala93 in L22 of E. coli. In this strain, therefore, the Gly93Glu change in L22 might contribute to the increase of macrolide resistance. The patient with NGU, whose specimen exhibited this strain of M. genitalium that harbored both the A2059G (E. coli numbering) mutation in the 23S rRNA gene and in which the Gly93Glu change in L22 was detected, was given a single dose of1 g azithromycin and was clinically cured of NGU. However, the present study suggests that M. genitalium strains with high-level macrolide resistance might have already emerged in clinical settings in Japan. The emergence and spread of such a clinical mutant could threaten the ability of macrolides to treat M. genitalium infections. We should continue monitoring macrolide resistance of M. genitalium clinical strains. The nonculture approach used in our study will be useful until culturing of mycoplasmas from clinical specimens and antimicrobial drug susceptibility testing can be performed easily in laboratories.
This study was supported in part by the Japan Society for the Promotion of Science, Japan, under a Grant-in-Aid for Scientific Research, (C) 22591788.
Yasushi Shimada, Takashi Deguchi, Keita Nakane, Mitsuru Yasuda, Shigeaki Yokoi, Shin-ichi Ito, Masahiro Nakano, Shin Ito, and Hiroaki Ishiko
Author affiliations: Gifu University, Gifu, Japan (Y. Shimada, T. Deguchi, K. Nakane, M. Yasuda, S. Yokoi, S.-I. Ito, M. Nakano); Mitsubishi Chemical Medience Corporation, Chiba, Japan (Y. Shimada, H. Ishiko); iClinic, Sendai, Japan (S. Ito)
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Address for correspondence: Takashi Deguchi, Department of Urology, Graduate School of Medicine, Gifu University, 1-1 Yanagido, Gifu City, Gifu 501-1194, Japan; email: email@example.com
Table. Mutations in the 23S rRNA gene and amino acid changes in L4 and L22 ribosomal proteins of 25 Mycoplasma genitalium strains in the pretreatment urine specimens of men with nongonococcal urethritis, Japan Mutation Amino acid change No. urine in the 23S specimens rRNA gene * L4 L22 1 A2059G -- Gly93Glu/Asp109Glu 1 T2185G Val84Gly -- 1 T2185G GLu128Gly -- 2 T2185G -- -- 1 -- Pro81Ser -- 1 -- Tyr135Pro -- 1 -- -- Ser81Thr 1 -- -- Met82Lys 1 -- -- Asn112Asp 1 -- -- Arg114Lys 14 -- -- -- * Nucleotide position in the 23S rRNA gene is according to Escherichia coli numbering. --, identical to the type strain.
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|Author:||Shimada, Yasushi; Deguchi, Takashi; Nakane, Keita; Yasuda, Mitsuru; Yokoi, Shigeaki; Ito, Shin-ichi;|
|Publication:||Emerging Infectious Diseases|
|Article Type:||Letter to the editor|
|Date:||Jun 1, 2011|
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