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Frequency of Chlamydia trachomatis in Ureaplasma-positive healthy women attending their first prenatal visit in a community hospital in Sapporo, Japan
© Yamazaki et al; licensee BioMed Central Ltd. 2012
Received: 31 January 2012
Accepted: 2 April 2012
Published: 2 April 2012
Although Chlamydia trachomatis is the most commonly reported pathogen that causes urogenital infection such as urethritis or cervicitis, Ureaplasma parvum and Ureaplasma urealyticum, which are commensals in the genital tract, have also now been recognized as contributors to urogenital infection. However, whether the presence of either U. parvum or U. urealyticum is related to that of C. trachomatis in the urogenital tract remains unknown. We therefore attempted to estimate by PCR the prevalence of C. trachomatis, U. parvum and U. urealyticum in endocervical samples obtained from healthy women attending their first prenatal visit in Sapporo, Japan.
The samples were taken from 303 apparently healthy women, and the extracted DNAs (n = 280) were used for PCR detection targeting C. trachomatis, U. parvum and U. urealyticum. Statistical analysis of the data was performed by Fisher's exact test.
PCR detection revealed that the prevalence of C. trachomatis, U. parvum and U. urealyticum was 14.3% (40/280), 41.7% (117/280) and 8.9% (25/280), respectively. C. trachomatis ompA genotype D was most frequently identified. Surprisingly, either C. trachomatis or Ureaplasma spp. was detected in almost half of the healthy women. Mixed infection of C. trachomatis with either U. parvum or U. urealyticum was also observed in 9.2% (26/280) of the women. There was a significant association between C. trachomatis and either U. parvum (p = 0.023) or Ureaplasma total (p = 0.013), but not U. urealyticum (p = 0.275).
This study demonstrated that the presence of Ureaplasma had a significant effect on the presence of C. trachomatis in the genital tract of healthy women, suggesting that mixed infection is an important factor in bacterial pathogenesis in the genital tract.
Urogenital tract infections are a major cause of morbidity in sexually active individuals worldwide, therefore, the World Health Organization has stated that sexually transmitted diseases (STDs) rank second in importance after cancer as treatable diseases in women. In particular, Chlamydia trachomatis is the leading cause of bacterial STD, with an estimated 5 million new cases annually worldwide [1–3]. C. trachomatis infection can cause testicular atrophy, epididymitis and orchitis in men, and ductal obstruction, pelvic inflammatory disease, tubal occlusion and extrauterine pregnancy in women [4–9]. However, the aetiology of most cases of chlamydial infection is undetermined and it could be multifactorial in nature, because of complications with commensal bacteria or mixed infections with other pathogens [10–12]. Therefore, the prevalence of C. trachomatis and other pathogens needs to be investigated.
Ureaplasma are currently separated into two species: Ureaplasma urealyticum and Ureaplasma parvum, which are both thought to be genital tract commensals [13–17]. They are commonly found in healthy persons, therefore, their pathogenic role can be difficult to prove in a small population of individuals. Meanwhile, several studies have reported that Ureaplasma are associated with some diseases including non-gonococcal urethritis, pregnancy complications and prenatal infections, more often than are normal flora [18–20]. Thus, it might be that Ureaplasma perturb homeostasis in the genital tract, which provides a survival advantage for C. trachomatis. However, data regarding mixed infection of C. trachomatis with Ureaplasma are limited [13–15].
In the present study, we therefore attempted to estimate by PCR and culture (C. trachomatis, inclusion forming assay; Ureaplasma, urease test), the prevalence of C. trachomatis, U. parvum and U. urealyticum in healthy women attending their first prenatal visit at a community hospital in Sapporo, Japan.
C. trachomatis D/UW3 Cx strain (VR-855) and U. parvum (ATCC-27813) were purchased from ATCC (Manassas, VA, USA). C. trachomatis and U. parvum were propagated in the HEp-2 cell culture system  and PPLO medium [1.5% (w/v) PPLO powder, 20% (v/v) horse serum, 5% (w/v) yeast extract, 1% (w/v) urea, 0.1% (w/v) phenol red, antibiotics (10 μg/ml vancomycin; 1 μg/ml amphotericin B), pH 6.0], respectively. The numbers of infectious progenies for C. trachomatis were determined as inclusion forming units (IFU) by counting chlamydial inclusions formed in HEp-2 cells using fluorescein isothiocyanate (FITC)-conjugated monoclonal anti-Chlamydia antibody specific to Chlamydia lipopolysaccharide (LPS) (Denka Seiken Co. Ltd., Tokyo, Japan) . The numbers U. parvum were also determined as colony-forming units (CFU) by counting colonies formed on the PPLO agar under a phase-contrast microscope.
Three hundred and three samples were obtained from apparently healthy women attending their first prenatal visit at Toho Obstetrics and Gynecology Hospital [number of deliveries, 1,332 per year (2010); number of caesarean sections, 310 per year (2010); number of vacuum extractions, 106 per year (2010)], located on the outskirts of Sapporo City, Japan, from July 2010 to September 2010. The average age (± SD) of healthy women attending this hospital was 28.28 ± 5.25 years, and the age distribution was as follows: 94 (20-24 years), 93 (25-29 years), 59 (30-34 years), 25 (35-40 years), and nine (> 40 years). The samples were collected by scraping the endocervix of each woman with a sterile cotton applicator. The applicator was immediately immersed and resuspended in 1 ml sucrose-phosphate-glutamic acid buffer [SPG: 0.2 M sucrose, 3.8 mM KH2PO4, 6.7 mM Na2HPO4, 5 mM L-glutamic acid (pH 7.4)], and stored at -80°C until use.
Written informed consent was obtained from all women, and the study was approved by the ethics committees of the Faculty of Health Sciences, Hokkaido University and Toho Obstetrics and Gynecology Hospital.
One hundred microlitres of SPG solution in each sample was used for DNA extraction using a QIAmp DNA mini kit (Qiagen, Valencia, CA, USA), according to manufacturer's instructions. The solution was centrifuged at 18,900 × g for 30 min. Pellets were then used for DNA extraction. The DNA was eluted in 50 μl of the elution buffer supplied with the kit, quantitated spectrophotometrically and stored at -20°C until use.
PCR detection and lineage analysis with ompA full sequences
Primer sequences and PCR conditions used for this study
Reference [Reference number]
5'-AGA GTT TGA TYM TGG CTC AG-3'*
Horn et al., 1999 
5'-CAK AAA GGA GGT CC-3'**
5'-ATG AAA AAA CTC TTG AAA TCG G-3'
Jurstrand et al., 2010 
5'-ACT GTA ACT GCG TAT TTG TCT G-3'
MBA gene with
5'-(T/C)AA ATC TTA GTG TTC ATA TTT TTT AC-3'
Kong et al., 2000 
it upstream region***
5'-GTA AGT GCA GCA TTA AAT TCA ATG-3'
MBA gene with it upstream region
5'-GTA TTT GCA ATC TTT ATA TGT TTT CG-3'
Kong et al., 2000 
5'-TTT GTT GTT GCG TTT TCT-3'
PCR detection limit for C. trachomatis and ureaplasmas
To determine the detection limit of PCR for C. trachomatis and Ureaplasma spp., spike experiments were performed. U. parvum was used as a representative Ureaplasma. Several sets of 100 μl of SPG solution in the pooled swab samples, which proved negative for C. trachomatis and Ureaplasma, were prepared. The sets were spiked with serial dilutions of either C. trachomatis VR-855 from 10-2 to 104 IFU or U. parvum ATCC-27813 from 10-1 to 105 CFU per sample. The DNA extraction of spiked samples, as well as from clinical specimen, was used for the PCR-detection method with primer sets targeting to C. trachomatis ompA and Ureaplasma MBA as described above.
The presence of infectious C. trachomatis in the samples confirmed as C. trachomatis-PCR positive was determined by inclusion formation assay on HEp-2 cells. The presence of viable Ureaplasma in the samples confirmed as either U. parvum or U. urealyticum PCR-positive was also determined using a urease assay as follows. In brief, a sample solution of 5 μl was diluted to 100 μl with SPG, and then passed through a filter with a 0.22-μm pore size. The filtrate was cultured in a total of 200 μl of PPLO medium at 37°C for 7 days. Samples that turned from yellow to red after the incubation were considered Ureaplasma positive.
Comparison between the frequency of C. trachomatis and that of U. parvum or U. urealyticum was done by Fisher's exact test (two-way ANOVA; Statview, Abacus Concepts Inc., Piscatway, NJ, USA). A p value < 0.05 was considered significant.
Results and discussion
Quality control of DNA extracted from endocervical samples
We assessed by PCR amplification the bacterial flora in the genital tract, to confirm whether extracted DNA was suitable for PCR amplification that target C. trachomatis or Ureaplasma spp. Three hundred and three samples were individually assessed by PCR with a primer set targeting bacterial 16S rRNA. The average amount of DNA was 63.64 ± 89.16 ng/μl, which indicated successful DNA extraction, therefore, it was expected that all samples would be available for PCR. However, in 23 samples (9.2%) PCR failed to amplify 16S rRNA gene, even though the amount of extracted DNA was never low. Therefore, the 23 samples without amplification were omitted and the remaining 280 were used for this study. Standard PCR techniques, which can be applied to analyse the entire microorganism community of complex biological samples obtained from living individuals, has been universally used. However, it is well known that haemoglobin, lactoferrin, heparin, and bile acids, which are ubiquitous to environments such as the genital tract, inhibit PCR amplification . This suggests that it is absolutely necessary to check the DNA quality carefully to confirm successful PCR amplification from genital swab samples.
PCR detection of C. trachomatis, U. parvum and U. urealyticum
Prevalence of C. trachomatis, U. parvum and U. urealyticum
PCR detection also revealed that the prevalence of U. parvum and U. urealyticum was 41.7% and 8.9%, respectively. Other studies with healthy women also have reported that the detection frequency of U. parvum and U. urealyticum was estimated at ~50% (57 and 87% Australia [13, 48]; 52% Japan ; 33.2 and 86.8% China ; 86% Italy ; 17.9% Poland ) and 10% (6.1-19% Australia ; 8.7% Japan ; 4.6-10.5% China ; 14% Italy ; 2.6% Poland ). The findings with our data suggested that the distribution of Ureaplasma is spreading worldwide and that the species are commonly found in healthy people as presumably commensal bacteria, therefore, their pathogenic role would be minimal [53–56]. Nevertheless, it has been increasingly reported that Ureaplasma spp. are associated with non-gonococcal urethritis, chorioamnionitis, preterm birth, perinatal morbidity, and mortality, more often than are normal flora [53–55]. Thus, our knowledge regarding the pathogenesis of Ureaplasma still remains paradoxical and is limited, suggesting that further, larger epidemiological studies with healthy people and patients with urogenital disorders are needed.
The gold standard for bacterial detection from clinical specimens is probably culture; therefore, we also assessed whether C. trachomatis and Ureaplasma spp. in PCR-positive samples could be detected by using biological detection systems, IFU assay and urease assay, respectively. However, contrary to our expectation, the detection frequencies of C. trachomatis and Ureaplasma spp. in PCR-positive samples decreased to 30% and 2%, respectively. Although it is necessary to clarify the exact reason, it is possible that freeze-thawing of samples crucially caused a decrease in detection frequencies.
Mixed infection of C. trachomatis and Ureaplasma
Correlation between prevalence of C. trachomatis and ureaplasmas in the genital swabs
Result for C. trachomatis DNA (n)
No. (%) of samples for U. parvum DNA testing
No. (%) of samples for U. urealyticum DNA testing
No. (%) of samples for Ureaplasma total DNA testing
Why does C. trachomatis co-infect with U. parvum in the genital tract? So far, we do not have any definite explanation. However, it is possible that the presence of U. parvum could provide some advantages for survival of C. trachomatis in the genital tract, possibly through directly or indirectly supplying tryptophan to overcome the depletion of this amino acid inside the cells by interferon γ exposure [59, 60].
Endocervical samples were taken from 303 women attending their first prenatal visit at a community hospital in Sapporo, Japan, and the extracted DNAs (n = 280), amenable to 16S rRNA PCR amplification, were analysed by PCR that targeted C. trachomatis, U. parvum and U. urealyticum. The prevalence of C. trachomatis, U. parvum and U. urealyticum was 14.3%, 41.7% and 8.9%, respectively. Mixed infection with C. trachomatis with either U. parvum or U. urealyticum was observed in 9.2% of the study population. Interestingly, there was a statistical correlation between the frequency of C. trachomatis and either U. parvum (p = 0.023) or Ureaplasma total (p = 0.013), but not U. urealyticum (p = 0.275). Thus, this study demonstrated that the presence of Ureaplasma had a significant effect on the presence of C. trachomatis in the genital tract of healthy women.
We thank the staff at the Department of Medical Laboratory Science, Faculty of Health Sciences, Hokkaido University, for their assistance throughout this study. This study was supported in part by grants-in-aid for scientific research (21590474), and a research grant from the Institute for Fermentation, Osaka, Japan.
- WHO: Global Prevalence and incidence of Curable Stis. 2001, Geneva: World Health OrganizationGoogle Scholar
- WHO: Priority eye diseases. 2008, [WWW document]. URL http://www.who.int/blindness/causes/priority/en/index2.html Google Scholar
- Horner P: The case for further treatment studies of uncomplicated genital Chlamydia trachomatis infection. Sex Transm Infect. 2006, 82: 340-343. 10.1136/sti.2005.019158.View ArticlePubMedPubMed CentralGoogle Scholar
- Gallegos G, Ramos B, Santiso R, Goyanes V, Gosalvez J, Fernandez JL: Sperm DNA fragmentation in infertile men with genitourinary infection by Chlamydia trachomatis and Mycoplasma. Fertil Steril. 2008, 90: 328-334. 10.1016/j.fertnstert.2007.06.035.View ArticlePubMedGoogle Scholar
- Bezold G, Politch JA, Kiviat NB, Kuypersm JM, Wolff H, Anderson DJ: Prevalence of sexually transmissible pathogens in semen from asymptomatic male infertility patients with and without leukocytospermia. Fertil Steril. 2007, 87: 1087-1097. 10.1016/j.fertnstert.2006.08.109.View ArticlePubMedPubMed CentralGoogle Scholar
- Jakiel G, Robak-Cholubek D, Wieczorek P, Bokiniec M: Evaluation of some parameters of human semen with positive chlamydial reaction. Ann Univ Mariae Curie Sklodowska. 2004, 59: 61-64.Google Scholar
- Gdoura R, Keskes-Ammar L, Bouzid F, Eb F, Hammami A, Orfila J: Chlamydia trachomatis and male infertility in Tunisia. Eur J Contracept Reprod Health Care. 2001, 6: 102-107.View ArticlePubMedGoogle Scholar
- Custo GM, Lauro V, Saitto C, Frongillo RF: Chlamydial infection and male infertility: an epidemiological study. Arch Androl. 1989, 23: 243-248. 10.3109/01485018908986847.View ArticlePubMedGoogle Scholar
- Gump D, Gibson M, Ashikaga T: Evidence of prior pelvic inflammatory disease and its relationship to Chlamydia trachomatis antibody and intrauterine contraceptive device use in infertile women. Am J Obstet Gynecol. 1983, 146: 153-159.View ArticlePubMedGoogle Scholar
- Lusk MJ, Konecny P: Cervicitis: a review. Curr Opin Infect Dis. 2008, 21: 49-55.PubMedGoogle Scholar
- Marrazzo JM: Mucopurulent cervicitis: no longer ignored, but still misunderstood. Infect Dis Clin N America. 2005, 19: 333-349. 10.1016/j.idc.2005.03.009.View ArticleGoogle Scholar
- Debattista J, Gazzard CM, Wood RN, Allan JA, Allan JM, Scarman A, Mortlock M, Timms P, Knox CL: Interaction of microbiology and pathology in women undergoing investigations for infertility. Infect Dis Obstet Gynecol. 2004, 12: 135-145. 10.1080/10647440400020703.View ArticlePubMedPubMed CentralGoogle Scholar
- Kong F, Ma Z, James G, Gordon S, Gilbert GL: Species identification and subtyping of Ureaplasma parvum and Ureaplasma urealyticum using PCR-based assays. J Clin Microbiol. 2000, 38: 1175-1179.PubMedPubMed CentralGoogle Scholar
- Kong F, James G, Ma Z, Gordon S, Wang B, Gilbert GL: Phylogenetic analysis of Ureaplasma urealyticum--support for the establishment of a new species, Ureaplasma parvum. Int J Syst Bacteriol. 1999, 49: 1879-1889. 10.1099/00207713-49-4-1879.View ArticlePubMedGoogle Scholar
- Kong F, Zhu X, Wang W, Zhou X, Gordon S, Gilbert GL: Comparative analysis and serovar-specific identification of multiple-banded antigen genes of Ureaplasma urealyticum biovar 1. J Clin Microbiol. 1999, 37: 538-543.PubMedPubMed CentralGoogle Scholar
- Abele-Horn M, Wolff C, Dressel P, Pfaff F, Zimmermann A: Association of Ureaplasma urealyticum biovars with clinical outcome for neonates, obstetric patients, and gynecological patients with pelvic inflammatory disease. J Clin Microbiol. 1997, 35: 1199-1202.PubMedPubMed CentralGoogle Scholar
- Taylor-Robinson D, Furr PM: Genital Mycoplasma infections. Wien Klin Wochenschr. 1997, 109: 578-583.PubMedGoogle Scholar
- Ollikainen J, Heiskanen-Kosma T, Korppi M, Katila ML, Heinonen K: Clinical relevance of Ureaplasma urealyticum colonization in preterm infants. Acta Paediatr. 1998, 87: 1075-1078. 10.1111/j.1651-2227.1998.tb01417.x.View ArticlePubMedGoogle Scholar
- Tully JG: Current status of the mollicute flora of humans. Clin Infect Dis. 1993, 17 (Suppl 1): S2-S9.View ArticlePubMedGoogle Scholar
- Zheng X, Watson HL, Waites KB, Cassell GH: Serotype diversity and antigen variation among invasive isolates of Ureaplasma urealyticum from neonates. Infect Immun. 1992, 60: 3472-3474.PubMedPubMed CentralGoogle Scholar
- Kobayashi M, Ishida K, Matsuo J, Nakamura S, Nagasawa A, Motohashi K, Yao T, Hirai I, Yamamoto Y, Suzuki H, Shimizu C, Matsuno K, Yamaguchi H: Chlamydophila pneumoniae attachment and infection in low proteoglycan expressing human lymphoid Jurkat cells. Microb Pathog. 2011, 51: 209-216. 10.1016/j.micpath.2011.03.010.View ArticlePubMedGoogle Scholar
- Edgar RC: MUSCLE: multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Res. 2004, 32: 1792-1797. 10.1093/nar/gkh340.View ArticlePubMedPubMed CentralGoogle Scholar
- Mahony JB, Jang D, Chong S, Luinstra K, Sellors J, Tyndall M, Chernesky M: Detection of Chlamydia trachomatis, Neisseria gonorrhoeae, Ureaplasma urealyticum, and Mycoplasma genitalium in first-void urine specimens by multiplex polymerase chain reaction. Mol Diagn. 1997, 2: 161-168. 10.1016/S1084-8592(97)80024-0.View ArticlePubMedGoogle Scholar
- Jurstrand M, Christerson L, Klint M, Fredlund H, Unemo M, Herrmann B: Characterisation of Chlamydia trachomatis by ompA sequencing and multilocus sequence typing in a Swedish county before and after identification of the new variant. Sex Transm Infect. 2010, 86: 56-60. 10.1136/sti.2009.037572.View ArticlePubMedGoogle Scholar
- Horn M, Fritsche TR, Gauton RK, Schleifer KH, Wagner M: Novel bacterial endosymbionts of Acanthamoeba spp. related to the Paramecium caudatum symbiont Caedibacter caryohilus. Environ Microbiol. 1999, 1: 357-367. 10.1046/j.1462-2920.1999.00045.x.View ArticlePubMedGoogle Scholar
- Wilson IG: Inhibition and facilitation of nucleic acid amplification. Appl Environ Microbiol. 1997, 63: 3741-3751.PubMedPubMed CentralGoogle Scholar
- Magbanua JP, Goh BT, Michel CE, Aguirre-Andreasen A, Alexander S, Ushiro-Lumb I, Ison C, Lee H: Chlamydia trachomatis variant not detected by plasmid based nucleic acid amplification tests: molecular characterisation and failure of single dose azithromycin. Sex Transm Infect. 2007, 83: 339-343. 10.1136/sti.2007.026435.View ArticlePubMedPubMed CentralGoogle Scholar
- Skulnick M, Chua R, Simor AE, Low DE, Khosid HE, Fraser S, Lyons E, Legere EA, Kitching DA: Use of the polymerase chain reaction for the detection of Chlamydia trachomatis from endocervical and urine specimens in an asymptomatic low-prevalence population of women. Diagn Microbiol Infect Dis. 1994, 20: 195-201. 10.1016/0732-8893(94)90003-5.View ArticlePubMedGoogle Scholar
- Jurstrand M, Olcén P, Magnuson A, Jakobsson L, Fredlund H, Unemo M: Emergence of the new variant of Chlamydia trachomatis in a defined area of Sweden before 2002?. Sex Transm Infect. 2010, 86: 337-341. 10.1136/sti.2009.040196.View ArticlePubMedGoogle Scholar
- Ripa T, Nilsson PA: A Chlamydia trachomatis strain with a 377-bp deletion in the cryptic plasmid causing false-negative nucleic acid amplification tests. Sex Transm Dis. 2007, 34: 255-256.PubMedGoogle Scholar
- Stevens MP, Tan SE, Horvath L, Fairley CK, Garland SM, Tabrizi SN: Absence of a Chlamydia trachomatis variant, harbouring a deletion in the cryptic plasmid, in clients of a sexually transmissible infection clinic and antenatal patients in Melbourne. Commun Dis Intell. 2008, 32: 77-81.Google Scholar
- Kong F, Gilbert GL: Postgenomic taxonomy of human ureaplasmas - a case study based on multiple gene sequences. Int J Syst Evol Microbiol. 2004, 54: 1815-1821. 10.1099/ijs.0.63073-0.View ArticlePubMedGoogle Scholar
- Monecke S, Helbig JH, Jacobs E: Phase variation of the multiple banded protein in Ureaplasma urealyticum and Ureaplasma parvum. Int J Med Microbiol. 2003, 293: 203-211. 10.1078/1438-4221-00239.View ArticlePubMedGoogle Scholar
- Zimmerman CU, Stiedl T, Rosengarten R, Spergser J: Alternate phase variation in expression of two major surface membrane proteins (MBA and UU376) of Ureaplasma parvum serovar 3. FEMS Microbiol Lett. 2009, 292: 187-193. 10.1111/j.1574-6968.2009.01505.x.View ArticlePubMedGoogle Scholar
- Teng LJ, Ho SW, Ho HN, Liaw SJ, Lai HC, Luh KT: Rapid detection and biovar differentiation of Ureaplasma urealyticum in clinical specimens by PCR. J Form Med Assoc. 1995, 94: 396-400.Google Scholar
- Teng LJ, Zheng X, Glass JI, Watson HL, Tsai J, Cassell GH: Ureaplasma urealyticum biovar specificity and diversity are encoded in multiple-banded antigen gene. J Clin Microbiol. 1994, 32: 1464-1469.PubMedPubMed CentralGoogle Scholar
- Molano M, Meijer CJ, Weiderpass E, Arslan A, Posso H, Franceschi S, Ronderos M, Muñoz N, van den Brule AJV: The natural course of Chlamydia trachomatis infection in asymptomatic Colombian women: a 5-year follow-up study. J Infect Dis. 2005, 191: 907-916. 10.1086/428287.View ArticlePubMedGoogle Scholar
- Scott Lamontagne D, Baster K, Emmett L, Nichols T, Randall S, McLean L, Meredith P, Harindra V, Tobin JM, Underhill GS, Graham Hewitt W, Hopwood J, Gleave T, Ghosh AK, Mallinson H, Davies AR, Hughes G, Fenton KA: Incidence and reinfection rates of genital chlamydial infection among women aged 16-24 years attending general practice, family planning and genitourinary medicine clinics in England: a prospective cohort study by the chlamydia recall study advisory group. Sex Transm Infect. 2007, 2007 (83): 292-303.View ArticleGoogle Scholar
- Eggleston E, Rogers SM, Turner CF, Miller WC, Roman AM, Hobbs MM, Erbelding E, Tan S, Villarroel MA, Ganapathi L: Chlamydia trachomatis infection among 15- to 35-year-olds in Baltimore, MD. Sex Transm Dis. 2011, 38: 743-749.PubMedPubMed CentralGoogle Scholar
- Regan DG, Wilson DP, Hocking JS: Coverage is the key for effective screening of Chlamydia trachomatis in Australia. J Infect Dis. 2008, 198: 349-358. 10.1086/589883.View ArticlePubMedGoogle Scholar
- Ishi K, Suzuki F, Saito A, Kubota T: Prevalence of human papillomavirus, Chlamydia trachomatis, and Neisseria gonorrhoeae in commercial sex workers in Japan. Infect Dis Obstet Gynecol. 2000, 8: 235-239.PubMedPubMed CentralGoogle Scholar
- Tsunoe H, Tanaka M, Nakayama H, Sano M, Nakamura G, Shin T, Kanayama A, Kobayashi I, Mochida O, Kumazawa J, Naito S: High prevalence of chlamydia trachomatis, neisseria gonorrhoeae and mycoplasma genitalium in female commercial sex workers in Japan. Int J STD AIDS. 2000, 11: 790-794. 10.1258/0956462001915291.View ArticlePubMedGoogle Scholar
- Imai H, Shinohara H, Nakao H, Tsukino H, Hamasuna R, Katoh T: Prevalence and risk factors of asymptomatic chlamydial infection among students in Japan. Int J STD AIDS. 2004, 15: 408-414. 10.1258/095646204774195272.View ArticlePubMedGoogle Scholar
- Hamasuna R, Imai H, Tsukino H, Jensen JS, Osada Y: Prevalence of Mycoplasma genitalium among female students in vocational schools in Japan. Sex Transm Infect. 2008, 84: 303-305. 10.1136/sti.2007.028670.View ArticlePubMedGoogle Scholar
- Yamada T, Atsuki Y, Wakasaya A, Kobayashi M, Hirano Y, Ohwada M: Characteristics of patients with subchorionic hematomas in the second trimester. J Obstet Gynaecol Res. 2012, 38: 180-184. 10.1111/j.1447-0756.2011.01665.x.View ArticlePubMedGoogle Scholar
- Imai H, Nakao H, Shinohara H, Fujii Y, Tsukino H, Hamasuna R, Osada Y, Fukushima K, Inamori M, Ikenoue T, Katoh T: Population-based study of asymptomatic infection with Chlamydia trachomatis among female and male students. Int J STD AIDS. 2010, 21: 362-366. 10.1258/ijsa.2010.010026.View ArticlePubMedGoogle Scholar
- Ikehata M, Numazaki K, Chiba S: Analysis of Chlamydia trachomatis serovars in endocervical specimens derived from pregnant Japanese women. FEMS Immunol Med Microbiol. 2000, 27: 35-41. 10.1111/j.1574-695X.2000.tb01409.x.View ArticlePubMedGoogle Scholar
- De Francesco MA, Negrini R, Pinsi G, Peroni L, Manca N: Detection of Ureaplasma biovars and polymerase chain reaction-based subtyping of Ureaplasma parvum in women with or without symptoms of genital infections. Eur J Clin Microbiol Infect Dis. 2009, 28: 641-646. 10.1007/s10096-008-0687-z.View ArticlePubMedGoogle Scholar
- McIver CJ, Rismanto N, Smith C, Naing ZW, Rayner B, Lusk MJ, Konecny P, White PA, Rawlinson WD: Multiplex PCR testing detection of higher-than-expected rates of cervical mycoplasma, ureaplasma, and trichomonas and viral agent infections in sexually active australian women. J Clin Microbiol. 2009, 47: 1358-1363. 10.1128/JCM.01873-08.View ArticlePubMedPubMed CentralGoogle Scholar
- Kataoka S, Yamada T, Chou K, Nishida R, Morikawa M, Minami M, Yamada H, Sakuragi N, Minakami H: Association between preterm birth and vaginal colonization by mycoplasmas in early pregnancy. J Clin Microbiol. 2006, 44: 51-55. 10.1128/JCM.44.1.51-55.2006.View ArticlePubMedPubMed CentralGoogle Scholar
- Cao X, Wang Y, Hu X, Qing H, Wang H: Real-time TaqMan polymerase chain reaction assays for quantitative detection and differentiation of Ureaplasma urealyticum and Ureaplasma parvum. Diagn Microbiol Infect Dis. 2007, 57: 373-378. 10.1016/j.diagmicrobio.2006.09.006.View ArticlePubMedGoogle Scholar
- Ekiel AM, Friedek DA, Romanik MK, Jóźwiak J, Martirosian G: Occurrence of Ureaplasma parvum and Ureaplasma urealyticum in women with cervical dysplasia in Katowice, Poland. J Korean Med Sci. 2009, 24: 1177-1181. 10.3346/jkms.2009.24.6.1177.View ArticlePubMedPubMed CentralGoogle Scholar
- Grześko J, Elias M, Manowiec M, Gabryś MS: Genital mycoplasmas-morbidity and a potential influence on human fertility. Med Wieku Rozwoj. 2006, 10: 985-992.PubMedGoogle Scholar
- Viscardi RM: Ureaplasma species: role in diseases of prematurity. Clin Perinatol. 2010, 37: 393-409. 10.1016/j.clp.2009.12.003.View ArticlePubMedPubMed CentralGoogle Scholar
- Hartmann M: Genital mycoplasmas. J Dtsch Dermatol Ges. 2009, 7: 371-377.PubMedGoogle Scholar
- Denks K, Spaeth EL, Jõers K, Randoja R, Talpsep T, Ustav M, Kurg R: Coinfection of Chlamydia trachomatis, Ureaplasma urealyticum and human papillomavirus among patients attending STD clinics in Estonia. Scand J Infect Dis. 2007, 39: 714-718. 10.1080/00365540701199824.View ArticlePubMedGoogle Scholar
- Horner P, Thomas B, Gilroy CB, Egger M, Taylor-Robinson D: Role of Mycoplasma genitalium and Ureaplasma urealyticum in acute and chronic nongonococcal urethritis. Clin Infect Dis. 2001, 32: 995-1003. 10.1086/319594.View ArticlePubMedGoogle Scholar
- Yokoi S, Maeda S, Kubota Y, Tamaki M, Mizutani K, Yasuda M, Ito S, Nakano M, Ehara H, Deguchi T: The role of Mycoplasma genitalium and Ureaplasma urealyticum biovar 2 in postgonococcal urethritis. Clin Infect Dis. 2007, 45: 866-871. 10.1086/521266.View ArticlePubMedGoogle Scholar
- Nelson DE, Virok DP, Wood H, Roshick C, Johnson RM, Whitmire WM, Crane DD, Steele-Mortimer O, Kari L, McClarty G, Caldwell HD: Chlamydial IFN-gamma immune evasion is linked to host infection tropism. Proc Natl Acad Sci USA. 2005, 102: 10658-10663. 10.1073/pnas.0504198102.View ArticlePubMedPubMed CentralGoogle Scholar
- Morrison RP: New insights into a persistent problem - chlamydial infections. J Clin Invest. 2003, 111: 1647-1649.View ArticlePubMedPubMed CentralGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2334/12/82/prepub
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