Abstract
Mycoplasma agalactiae is a worldwide serious pathogen of small ruminants that usually spreads through the mammary route causing acute to subacute mastitis progressing to chronic persistent disease that is hard to eradicate. Knowledge of mechanisms of its pathogenesis and persistence in the mammary gland are still insufficient, especially the host-pathogen interplay that enables it to reside in a chronic subclinical state. This study reports transcriptome profiling of mammary tissue from udders of sheep experimentally infected with M. agalactiae type strain PG2 in comparison with uninfected control animals using Illumina RNA-sequencing (RNA-Seq). Several differentially expressed genes (DEGs) were observed in the infected udders and RT-qPCR analyses of selected DEGs showed their expression profiles to be in agreement with results from RNA-Seq. Gene Ontology (GO) analysis revealed majority of the DEGs to be associated with mycoplasma defense responses that are directly or indirectly involved in host innate and adaptive immune responses. Similar RNA-Seq analyses were also performed with spleen cells of the same sheep to know the specific systemic transcriptome responses. Spleen cells exhibited a comparatively lower number of DEGs suggesting a less prominent host response in this organ. To our knowledge this is the first study that describes host transcriptomics of M. agalactiae infection and the related immune-inflammatory responses. The data provides useful information to further dissect the molecular genetic mechanisms underlying mycoplasma mastitis, which is a prerequisite for designing effective intervention strategies.
Highlights
Mycoplasmas are one of the smallest and simplest microbes that cause difficult-to-eradicate chronic infections by complex unknown pathogenicity factors [1, 2]
M. agalactiae was continuously shed in the milk from the infected udders soon after 2 h of infection (4.00 x 106 cfu/ml) until the end of the experiment, that is, until Day 15 p.i. (3.08 x 108 cfu/ml), peak cfu values were reached on Day 2 p.i (4.44 x 1010 cfu/ml; Fig 1)
Except for one sheep that showed positive isolation of M. agalactiae starting from Day 7 p.i., the milk from left udder halves was negative for mycoplasmas at all tested time points, as was the case with non-infected control sheep for both udder halves
Summary
Mycoplasmas are one of the smallest and simplest microbes that cause difficult-to-eradicate chronic infections by complex unknown pathogenicity factors [1, 2]. Mycoplasma mastitis is one such worldwide problem. Amongst different causative species Mycoplasma bovis is the PLOS ONE | DOI:10.1371/journal.pone.0170015. Transcriptional Profiling of M. agalactiae-Infected Sheep and analysis, decision to publish, or preparation of the manuscript
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