Inflammatory Response of Primary Cultured Bovine Mammary Epithelial Cells to Staphylococcus aureus Extracellular Vesicles

Abstract

In dairy cows, <i>Staphylococcus aureus</i> (<i>S. aureus</i>) is among the most prevalent microorganisms worldwide, causing mastitis, an inflammation of the mammary gland. Production of extracellular vesicles (EVs) is a common feature of <i>S. aureus</i> strains, which contributes to its pathogenesis by delivering bacterial effector molecules to host cells. In the current study, we evaluated the differences between five <i>S. aureus</i> mastitis isolates regarding their EV production. We found that different mastitis-related <i>S. aureus</i> strains differ in their behaviour of shedding EVs, with M5512VL producing the largest amount of EVs containing alpha-haemolysin, a strong cytotoxic agent. We stimulated primary cultured bovine mammary epithelial cells (pbMECs) with EVs from the <i>S. aureus</i> strain M5512VL. After 24 h of incubation, we observed a moderate increase in gene expression of tumour necrosis factor-alpha (<i>TNF-α</i>) but, surprisingly, a lack of an associated pronounced pro-inflammatory response. Our results contribute to understanding the damaging nature of <i>S. aureus</i> in its capacity to effectively affect mammary epithelial cells.