Abstract
Staphylococcal enterotoxins (SEs) are powerful superantigenic toxins produced by Staphylococcus aureus (S. aureus). They can cause food poisoning and toxic shock. However, their impact on bovine mammary epithelial cells (bMECs) is still unknown. In this study, the distribution of SE genes was evaluated in 116 S. aureus isolates from bovine mastitis, and the most prevalent genes were seh (36.2%), followed by sei (12.1%), seg (11.2%), ser (4.3%), sec (3.4%), sea (2.6%) and sed (1.7%). To better understand the effect of staphylococcal enterotoxin H (SEH) on bMECs, the seh gene was cloned and inserted into the prokaryotic expression vector, pET28a, and transformed into Escherichia coli BL21 (DE3). The recombinant staphylococcal enterotoxin H (rSEH) was expressed and purified as soluble protein. Bioactivity analysis showed that rSEH possessed the activity of stimulating lymphocytes proliferation. The XTT assay showed that 100 μg/mL of rSEH produced the cytotoxic effect on bMECs, and fluorescence microscopy and flow cytometry analysis revealed that a certain dose of rSEH is effective at inducing bMECs apoptosis in vitro. This indicates that SEs can directly lead to cellular apoptosis of bMECs in bovine mastitis associated with S. aureus.
Highlights
Bovine mastitis is one of the most common economically important diseases in dairy cows throughout the world [1]
Genes coding the enterotoxins were identified in 116 S. aureus isolates associated with bovine mastitis, and the most commonly found was seh, which was followed by sei, seg, ser, sec, sea and sed (Table 1)
To the best of our knowledge, this is the first report that staphylococcal enterotoxin H can induce bovine mammary epithelial cells (bMECs) apoptosis
Summary
Bovine mastitis is one of the most common economically important diseases in dairy cows throughout the world [1]. The SEls toxins, both homologous and structurally similar to the SEs, either do not induce emesis or have not been confirmed to induce emesis, and these include SElJ, SElK, SElL, SElM, SElN, SElO, SElP, SElQ, SElS, SElU, SElV and SElX [10] Among these SEs and SEls genes, sea, sec, sed, see, seg, seh, sei, selj, selk, sell, selm, seln, selo, selp, selq and selu have been detected in S. aureus isolated from raw milk samples in earlier studies [11,12,13]. In order to better understand the role of SEs in bovine mastitis, the distribution of SE genes was detected in S. aureus isolates from mastitis, and the most prevalent SE gene, seh, was cloned and expressed in the prokaryotic expression system. The recombinant protein was purified and prepared and its bioactivity analyzed, and the viability and apoptosis of bovine mammary epithelial cells (bMECs) induced by recombinant staphylococcal enterotoxin H (rSEH) were studied
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