Characterization of hemotropic Mycoplasma (hemoplasma) isolates from Thai domestic pigs using the 23S ribosomal RNA gene

Hemotropic Mycoplasma, also known as hemoplasma, is a group of bacteria belonging to the Mollicutes, responsible for causing infectious anemia in various mammalian hosts, including pigs. Based on 16S rRNA gene characterization at the species level, porcine hemoplasmas have previously been classified as Mycoplasma (M.) suis, M. parvum, ‘Candidatus (Ca.) M. haemosuis’, and a potentially novel species. However, due to the high sequence similarity across hemoplasmas, the 16S rRNA gene cannot differentiate at the species level. Consequently, another genetic marker, the 23S rRNA gene, has been proposed for this purpose. In our study, we employed the 23S rRNA gene to characterize porcine hemoplasma isolates (n = 49) in our laboratory, using blast analysis, phylogenetic analysis and genetic network analysis. Through the approach using the 23S rRNA gene, we could identify at least six clusters or hemoplasma species from five groups of 16S rRNA sequences found in Thai pigs. Additionally, we could elucidate one ambiguous group from a previous study as M. parvum. This one ambiguous group potentially represented either M. suis or M. parvum group (ntST#4) from the 16S rRNA gene alone. Notably, two of the six clusters may represent putative novel species. These findings underscore the utility of the 23S rRNA gene in characterizing and surveying of hemoplasma infection in domestic pigs globally.