Abstract
Staphylococcus hyicus is the most common causative agent of exudative epidermitis (EE) in piglets. Staphylococcus hyicus can be grouped into toxigenic and non-toxigenic strains based on its ability to cause EE in pigs. However, the inflammatory response of piglets infected with toxigenic and non-toxigenic S. hyicus has not been elucidated. In this study, we evaluated the serum cytokine profile in piglets inoculated with toxigenic and non-toxigenic S. hyicus strains and recorded the clinical signs in piglets. Fifteen piglets were divided into three groups (n = 5) and inoculated with a toxigenic strain (ZC-4), a non-toxigenic strain (CF-1), and PBS (control), respectively. The changes in serum levels of cytokines (interleukin [IL]-1β, IL-4, IL-6, IL-8, IL-10, IL-12, granulocyte-macrophage colony-stimulating factor, interferon-γ, transforming growth factor-β1, and tumor necrosis factor-α) were evaluated using a cytokine array at 6, 24, 48, and 72 h post inoculation. The results showed that piglets infected with the toxigenic strain exhibited more severe clinical signs and higher mortality than those infected with the non-toxigenic strain. The serum levels of pro-inflammatory cytokine IL-1β were significantly increased in toxigenic-and non-toxigenic-strain-infected piglets compared to those in the control group (p < 0.05), while the anti-inflammatory cytokine IL-10 was significantly up-regulated only in toxigenic group than in control group (p < 0.05). These results indicated that piglets infected with toxigenic and non-toxigenic S. hyicus showed differential infection status and inflammatory responses. Both toxigenic- and non-toxigenic- S. hyicus infection could induce a pro-inflammatory reaction in piglets. In addition, the toxigenic strain induced a strong anti-inflammatory response in piglets as indicated by the increased serum level of IL-10, which may be associated with the severe clinical signs and increased mortality and may be the key cytokine response responsible for pathogenic mechanisms of S. hyicus.
Highlights
Staphylococcus hyicus, a gram-positive bacterium, is one of the major opportunistic and zoonotic pathogens causing exudative epidermitis (EE) in pigs, primarily suckling and newly weaned piglets [1, 2]
We evaluated the inflammatory response in piglets infected with toxigenic and non-toxigenic strains of S. hyicus by measuring the serum levels of cytokines, including pro-inflammatory cytokines (IL-1β, IL-6, IL-8, TNF-α, and IFNγ) and anti-inflammatory cytokines (IL-4, IL-10, and transforming growth factor (TGF)-β1)
The results demonstrated that piglets infected with toxigenic and non-toxigenic S. hyicus strains exhibited differential clinical signs and outcomes; the morbidity and mortality rates were higher in the toxigenic group than in the non-toxigenic group and control group, indicating the stronger virulence of the toxigenic strain ZC-4 than that of non-toxigenic strain CF-1
Summary
Staphylococcus hyicus, a gram-positive bacterium, is one of the major opportunistic and zoonotic pathogens causing exudative epidermitis (EE) in pigs, primarily suckling and newly weaned piglets [1, 2]. Exudative epidermitis is characterized by exfoliation of the skin; a thick, greasy, brown greasy exudate [3]; suppurative pneumonia; and sepsis [4], which may lead to dehydration and subsequent death [5]. Previous studies indicate that exfoliative toxin is the main virulence factor that induces the disease [7, 8]. According to its ability to induce EE and to produce exfoliative toxin, S. hyicus has been divided into toxigenic and non-toxigenic strains [8, 9]. At least five exfoliative toxins, named SHETB [10], ExhA, ExhB, ExhC, and ExhD [11] have been described. The exfoliative toxins selectively digested porcine desmoglein 1 directly in the porcine epidermis, causing separation of cells in the stratum spinosum and rapid intraepidermal spread of organisms [12]
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