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.

Proposal of Ureaplasma parvum sp. nov. and emended description of Ureaplasma urealyticum (Shepard et al. 1974) Robertson et al. 2001.

The phenotypic and genotypic properties of Ureaplasma urealyticum (family Mycoplasmataceae, order Mycoplasmatales, class Mollicutes) are reviewed here. The 14 recognized serovar standard strains found in humans exhibit no serological cross-reactivity with ureaplasmas from other hosts and uniquely express human immuoglobulin A1 protease activity. However, they exhibit many characteristics which place them in two distinct clusters known as the parvo biovar (or biovar 1 or B) and the T960T biovar (or biovar 2 or A). Established phenotypic markers of the biovars include clustering of antigenic types, polypeptide patterns of whole-cell preparations, differential inhibition by manganese, and polymorphism among their ureases, pyrophosphatases and diaphorases. Established genotypic markers of the biovars are DNA-DNA hybridization of 60% between biovars, and distinctive RFLP patterns and genome sizes. Divergent nucleotide sequences of several highly conserved genes attest to the phylogenetic distinctiveness of the two biovars. PCRs founded upon the sequences for 16S rRNA, the 16S-23S rRNA intergenic regions, the genus-defining urease, the serovar-defining, multiple-banded antigen genes or randomly amplified polymorphic DNA tests differentiate the biovars unambiguously. With the availability of rapid, reliable and economical tests for biovar determination, it is now appropriate to propose that the taxonomic status of U. urealyticum be emended. Serovar standard strains exhibiting traits of biovar parvo (serovars 1, 3, 6 and 14) will be designated as a separate species, Ureaplasma parvum sp. nov., as befits its smaller genome size. The serovar 3 standard (strain 27T) will be the type strain of U. parvum and is represented by ATCC 27815T and NCTC 11736T. Serovar standard strains exhibiting traits of biovar T960T (2, 4, 5, 7, 8T, 9, 10, 11, 12 and 13) will retain the U. urealyticum designation and type strain, the serovar 8 standard (strain T960T), represented by ATCC 27618T and NCTC 10177T.