Abstract
Among different bacteria colonizing the bovine uterus, Trueperella pyogenes is found to be associated with clinical endometritis (CE). The ability of cows to defend against T. pyogenes infections depends on the virulence of invading bacteria and on the host's innate immunity. Therefore, to gain insights into bacterial factors contributing to the interplay of this host pathogen, two strains of T. pyogenes were included in this study: one strain (TP2) was isolated from the uterus of a postpartum dairy cow developing CE and a second strain (TP5) was isolated from a uterus of a healthy cow. The two strains were compared in terms of their metabolic fingerprints, growth rate, virulence gene transcription, and effect on bovine endometrial epithelial cells in vitro. In addition, the effect of the presence of peripheral blood mononuclear cells (PBMCs) on the response of endometrial epithelial cells was evaluated. TP2, the strain isolated from the diseased cow, showed a higher growth rate, expressed more virulence factors (cbpA, nanH, fimE, and fimG), and elicited a higher mRNA expression of pro-inflammatory factors (PTGS2, CXCL3, and IL8) in bovine endometrial epithelial cells compared with TP5, the strain isolated from the healthy cow. The presence of PBMCs amplified the mRNA expression of pro-inflammatory factors (PTGS2, CXCL3, IL1A, IL6, and IL8) in bovine endometrial epithelial cells co-cultured with live TP2 compared with untreated cells, especially as early as after 4 h. In conclusion, particular strain characteristics of T. pyogenes were found to be important for the development of CE. Furthermore, immune cells attracted to the site of infection might also play an important role in up-regulation of the pro-inflammatory response in the bovine uterus and thus significantly contribute to the host-pathogen interaction.
Highlights
The subfertility of high-producing dairy cows represents a major obstacle to the profitability and sustainability of the dairy industry
This study indicates that peripheral blood mononuclear cells (PBMCs) might up-regulate the mRNA expression of PGTS2, which is a key enzyme of PG synthesis, in endometrial epithelial cells in response to T. pyogenes
The clinical T. pyogenes strain included in this study shows a higher expression of known virulence factors compared with a T. pyogenes strain isolated from a healthy cow, and distinct differences in the metabolic profile and growth characteristics
Summary
The subfertility of high-producing dairy cows represents a major obstacle to the profitability and sustainability of the dairy industry. Among the most common reasons for subfertility are postpartum uterine diseases caused by uterine bacterial infections after parturition (Sheldon et al, 2009). Up to 50% of all dairy cows develop uterine inflammatory diseases, such as metritis, and clinical or subclinical endometritis (Sheldon et al, 2009). The pathogenicity of T. pyogenes is attributed to pyolysin (PLO), which causes cytolysis of host cells (Jost et al, 1999; Amos et al, 2014). T. pyogenes is associated with severe endometritis, it has been isolated from cows without signs of uterine disease at puerperium (Silva et al, 2008; Santos et al, 2010; Wagener et al, 2015)
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