Development of an enzyme-linked immunosorbent assay for serotyping ureaplasma urealyticum strains using monoclonal antibodies

Ureaplasma infections: update on epidemiology, antimicrobial resistance, and pathogenesis

Human Ureaplasma species are being increasingly recognized as opportunistic pathogens in human genitourinary tract infections, infertility, adverse pregnancy, neonatal morbidities, and other adult invasive infections. Although some general reviews have focused on the detection and clinical manifestations of Ureaplasma spp., the molecular epidemiology, antimicrobial resistance, and pathogenesis of Ureaplasma spp. have not been adequately explained. The purpose of this review is to offer valuable insights into the current understanding and future research perspectives of the molecular epidemiology, antimicrobial resistance, and pathogenesis of human Ureaplasma infections. This review summarizes the conventional culture and detection methods and the latest molecular identification technologies for Ureaplasma spp. We also reviewed the global prevalence and mechanisms of antibiotic resistance for Ureaplasma spp. Aside from regular antibiotics, novel antibiotics with outstanding in vitro antimicrobial activity against Ureaplasma spp. are described. Furthermore, we discussed the pathogenic mechanisms of Ureaplasma spp., including adhesion, proinflammatory effects, cytotoxicity, and immune escape effects, from the perspectives of pathology, related molecules, and genetics.

The Human Ureaplasma Species as Causative Agents of Chorioamnionitis

The human Ureaplasma species are the most frequently isolated microorganisms from the amniotic fluid and placentae of women who deliver preterm and are also associated with spontaneous abortions or miscarriages, neonatal respiratory diseases, and chorioamnionitis. Despite the fact that these microorganisms have been habitually found within placentae of pregnancies with chorioamnionitis, the role of Ureaplasma species as a causative agent has not been satisfactorily explained. There is also controversy surrounding their role in disease, particularly as not all women infected with Ureaplasma spp. develop chorioamnionitis. In this review, we provide evidence that Ureaplasma spp. are associated with diseases of pregnancy and discuss recent findings which demonstrate that Ureaplasma spp. are associated with chorioamnionitis, regardless of gestational age at the time of delivery. Here, we also discuss the proposed major virulence factors of Ureaplasma spp., with a focus on the multiple-banded antigen (MBA), which may facilitate modulation/alteration of the host immune response and potentially explain why only subpopulations of infected women experience adverse pregnancy outcomes. The information presented within this review confirms that Ureaplasma spp. are not simply "innocent bystanders" in disease and highlights that these microorganisms are an often underestimated pathogen of pregnancy.

High-resolution melt PCR analysis for genotyping of Ureaplasma parvum isolates directly from clinical samples

Ureaplasma sp. infection in neonates and adults underlies a variety of disease pathologies. Of the two human Ureaplasma spp., Ureaplasma parvum is clinically the most common. We have developed a high-resolution melt (HRM) PCR assay for the differentiation of the four serovars of U. parvum in a single step. Currently U. parvum strains are separated into four serovars by sequencing the promoter and coding region of the multiple-banded antigen (MBA) gene. We designed primers to conserved sequences within this region for PCR amplification and HRM analysis to generate reproducible and distinct melt profiles that distinguish clonal representatives of serovars 1, 3, 6, and 14. Furthermore, our HRM PCR assay could classify DNA extracted from 74 known (MBA-sequenced) test strains with 100% accuracy. Importantly, HRM PCR was also able to identify U. parvum serovars directly from 16 clinical swabs. HRM PCR performed with DNA consisting of mixtures of combined known serovars yielded profiles that were easily distinguished from those for single-serovar controls. These profiles mirrored clinical samples that contained mixed serovars. Unfortunately, melt curve analysis software is not yet robust enough to identify the composition of mixed serovar samples, only that more than one serovar is present. HRM PCR provides a single-step, rapid, cost-effective means to differentiate the four serovars of U. parvum that did not amplify any of the known 10 serovars of Ureaplasma urealyticum tested in parallel. Choice of reaction reagents was found to be crucial to allow sufficient sensitivity to differentiate U. parvum serovars directly from clinical swabs rather than requiring cell enrichment using microbial culture techniques.

Development of a multilocus sequence typing scheme for Ureaplasma

Ureaplasma is a commensal of the human urogenital tract but is always associated with invasive diseases such as non-gonococcal urethritis and infertility adverse pregnancy outcomes. To better understand the molecular epidemiology and population structure of Ureaplasma, a multilocus sequence typing (MLST) scheme based on four housekeeping genes (ftsH, rpL22, valS, thrS) was developed and validated using 283 isolates, including 14 serovars of reference strains and 269 strains obtained from clinical patients. A total of 99 sequence types (STs) were revealed: the 14 type strains of the Ureaplasma serovars were assigned to 12 STs, and 87 novel and special STs appeared among the clinical isolates. ST1 and ST22 were the predominant STs, which contained 68 and 70 isolates, respectively. Two clonal lineages (CC1 and CC2) were shown by eBURST analysis, and linkage disequilibrium was revealed through a standardized index of association (I A (S)). The neighbor-joining tree results of 14 Ureaplasma serovars showed two genetically significantly distant clusters, which was highly congruent with the species taxonomy of ureaplasmas [Ureaplasma parvum (UPA) and Ureaplasma urealyticum (UUR)]. Analysis of the biotypes of 269 clinical isolates revealed that all the isolates of CC1 were UPA and those of CC2 were UUR. Additionally, CC2 was found more often in symptomatic patients with vaginitis, tubal obstruction, and cervicitis. In conclusion, this MLST scheme is adequate for investigations of molecular epidemiology and population structure with highly discriminating capacity.

Extensive horizontal gene transfer in ureaplasmas from humans questions the utility of serotyping for diagnostic purposes

Ureaplasma parvum and Ureaplasma urealyticum are sexually transmitted, opportunistic pathogens of the human urogenital tract. There are 14 known serovars distributed between the two species. For decades, it has been postulated based upon limited data that virulence is related to serotype specificity. The results were often inconclusive due to the small sample size and extensive cross-reactivity between certain serovars. We developed real-time quantitative PCRs that allow reliable differentiation of the two species and type strains of each of the 14 serovars. To investigate species and serovar distributions, we typed 1,061 clinical isolates of human ureaplasmas from diverse patient populations. There was only a tenuous association between individual Ureaplasma serovars and certain patient populations. This may in part be explained by the fact that almost 40% of the isolates were genetic mosaics, apparently arising from the recombination of multiple serovars. This explains the extensive cross-reactivity based upon serotyping and the lack of consistent association of given serotypes with disease.

Frequency of ureaplasma serovars in respiratory secretions of preterm infants at risk for bronchopulmonary dysplasia

OBJECTIVE

Ureaplasma respiratory tract colonization is associated with bronchopulmonary dysplasia (BPD) in preterm infants. Whether the 4 Ureaplasma parvum and 10 Ureaplasma urealyticum serovars differ in virulence is unknown. This study was conducted to determine the distribution of Ureaplasma serovars in respiratory secretions of a prospective cohort of preterm infants and to assess whether any of the serovars are associated with BPD.

METHODS

Serial endotracheal and/or nasopharyngeal aspirates were obtained for Ureaplasma culture and PCR from 136 infants of gestational age <33 weeks. All positive samples were speciated and serovars were determined by real-time PCR.

RESULTS

A total of 51 (37.5%) infants were Ureaplasma-positive one or more times during the first month of life. Respiratory colonization was inversely related to gestational age. Sixty-five percent of infants <26 weeks compared with 31% infants ≥ 26 weeks were culture or PCR positive. U. parvum was more common (N = 32, 63%) than U. urealyticum (N = 17, 33%); both species were present in 2 samples. Serovars 3 and 6 alone and in combination accounted for 96% U. parvum isolates. U. urealyticum isolates were commonly a mixture of multiple serovars, with serovar 11 alone or combined with other serovars (10/17, 59%) being the most common serovar. No individual species or serovars or serovar mixtures were associated with moderate-to-severe BPD.

CONCLUSIONS

U. parvum serovars 3 and 6 and U. urealyticum serovar 11 were the most common serovars detected in respiratory samples from a prospective cohort of preterm infants.

Production of recombinant antigens of Ureaplasma parvum serotypes 3 and 6 for development of a serological assay

Recombinant antigens of Ureaplasma parvum serotypes 3 and 6 were produced in order to develop a serological assay for Ureaplasma antibody detection. The genes of the multiple banded antigen (MBA) were amplified by PCR and cloned in a pTrcHis TOPO plasmid. Purified recombinant proteins were evaluated in Western blotting and enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies and human sera. Our approach was successful in the production of the recombinant MBAs (rMBAs) for serotypes 3 and 6. The antigens tested positive with serotype-specific monoclonal antibodies in Western blotting and in ELISA. Prominent reactions were detected with the rMBAs and their homologous monoclonal antibodies. Strong cross-reactions were visible in ELISA between rMBA 3 and the monoclonal antibodies from the other U. parvum serotypes. A weak cross-reaction was seen with rMBA 3 and the monoclonal antibody from serotype 4. rMBA 6 showed cross-reaction only with the monoclonal antibody from U. parvum serotype 1. Fifty-one percent of the sera obtained from culture-positive women reacted with one or both rMBAs. Only three (15%) of the sera from culture-negative women reacted with the rMBA. The positive reactions were observed only with rMBA 6. These preliminary tests showed the potential usefulness of the rMBAs produced for detecting an antibody response against Ureaplasma antigens.

Comparison of two methods for serotyping Ureaplasma urealyticum clinical isolates

A newly developed enzyme linked immunosorbent assay (ELISA) method using monoclonal antibodies (MAbs) to the 14 serotypes of Ureaplasma urealyticum was compared to immunofluorescence assay (IFA) for serotyping U. urealyticum clinical isolates. Of the 102 vaginal isolates of U. urealyticum, five strains were lost and were excluded from analysis. Of the 97 strains analysed, a total of 86 (89%) strains were typeable by ELISA and a total of 89 (92%) strains were typeable by IFA. Eighty-six strains were typeable by both methods, three by IFA only and eight strains were not typeable neither by ELISA nor by IFA. Of the 86 strains typeable by both methods, complete concordance in serotyping results was found. The three strains not typeable by ELISA were typeable as serotype 4 by IFA. These three strains were reanalysed by ELISA after major modifications of the antigen preparation and were typeable as serotype 4. In conclusion, the ELISA was found suitable for serotyping clinical isolates. However, since the ELISA had a somewhat lower performance than IFA, strains not typeable by ELISA, should be retested by another technique such as IFA.