This work reports the results of analyses of three complete mycoplasma genomes, a pathogenic (7448) and a nonpathogenic (J) strain of the swine pathogenMycoplasma hyopneumoniaeand a strain of the avian pathogenMycoplasma synoviae; the genome sizes of the three strains were 920,079 bp, 897,405 bp, and 799,476 bp, respectively. These genomes were compared with other sequenced mycoplasma genomes reported in the literature to examine several aspects of mycoplasma evolution. Strain-specific regions, including integrative and conjugal elements, and genome rearrangements and alterations in adhesin sequences were observed in theM. hyopneumoniaestrains, and all of these were potentially related to pathogenicity. Genomic comparisons revealed that reduction in genome size implied loss of redundant metabolic pathways, with maintenance of alternative routes in different species. Horizontal gene transfer was consistently observed betweenM. synoviaeandMycoplasma gallisepticum. Our analyses indicated a likely transfer event of hemagglutinin-coding DNA sequences fromM. gallisepticumtoM. synoviae.

The MIC for streptomycin in the presence of efflux pump (EP) inhibitors and the sequencing of rpsL , rrs , and gidB genes provided evidence for the possible participation of EP in low-level streptomycin (STR) resistance of some isolates without mutations. Mutation in the gidB gene and an EP could act synergistically to confer low STR resistance.

Mutations related to streptomycin resistance in the rpsL and rrs genes are well known and can explain about 70% of this phenotypic resistance. Recently, the gidB gene was found to be associated with low-level streptomycin resistance in Mycobacterium tuberculosis . Mutations in gidB have been reported with high frequency, and this gene appears to be very polymorphic, with frameshift and point mutations occurring in streptomycin-susceptible and streptomycin-resistant strains. In this study, mutations in gidB appeared in 27% of streptomycin-resistant strains that contained no mutations in the rpsL or rrs genes, and they were associated with low-level streptomycin resistance. However, the association of certain mutations in gidB with streptomycin resistance needs to be further investigated, as we also found mutations in gidB in streptomycin-susceptible strains. This occurred only when the strain was resistant to rifampin and isoniazid. Two specific mutations appeared very frequently in this and other studies of streptomycin-susceptible and -resistant strains; these mutations were not considered related to streptomycin resistance, but as a polymorphism. We stratified the strains according to the different phylogenetic lineages and showed that the gidB ¹⁶ polymorphism (16G allele) was exclusively present in the Latin American-Mediterranean (LAM) genotype, while the gidB ⁹² polymorphism (92C allele) was associated with the Beijing lineage in another population. In the sample studied, the two characterized single-nucleotide polymorphisms could distinguish LAM and Beijing lineages from the other lineages.

Background: Mycoplasma hyopneumoniae,Mycoplasma flocculareandMycoplasma hyorhinislive in swine respiratory tracts.M. flocculare, a commensal bacterium, is genetically closely related toM. hyopneumoniae, the causative agent of enzootic porcine pneumonia.M. hyorhinisis also pathogenic, causing polyserositis and arthritis. In this work, we present the genome sequences ofM. flocculareandM. hyopneumoniaestrain 7422, and we compare these genomes with the genomes of otherM. hyoponeumoniaestrain and to the aM. hyorhinisgenome. These analyses were performed to identify possible characteristics that may help to explain the different behaviors of these species in swine respiratory tracts.Results: The overall genome organization of three species was analyzed, revealing that the ORF clusters (OCs) differ considerably and that inversions and rearrangements are common. AlthoughM. flocculareandM. hyopneumoniaedisplay a high degree of similarity with respect to the gene content, only some genomic regions display considerable synteny. Genes encoding proteins that may be involved in host-cell adhesion inM. hyopneumoniaeandM. floccularedisplay differences in genomic structure and organization. Some genes encoding adhesins of the P97 family are absent inM. flocculareand some contain sequence differences or lack of domains that are considered to be important for adhesion to host cells. The phylogenetic relationship of the three species was confirmed by a phylogenomic approach. The set of genes involved in metabolism, especially in the uptake of precursors for nucleic acids synthesis and nucleotide metabolism, display some differences in copy number and the presence/absence in the three species.Conclusions: The comparative analyses of three mycoplasma species that inhabit the swine respiratory tract facilitated the identification of some characteristics that may be related to their different behaviors.M. hyopneumoniaeandM. floccularedisplay many differences that may help to explain why one species is pathogenic and the other is considered to be commensal. However, it was not possible to identify specific virulence determinant factors that could explain the differences in the pathogenicity of the analyzed species. TheM. hyorhinisgenome contains differences in some components involved in metabolism and evasion of the host’s immune system that may contribute to its growth aggressiveness. Several horizontal gene transfer events were identified. The phylogenomic analysis placesM. hyopneumoniae, M. flocculareandM. hyorhinisin the hyopneumoniae clade.