Abstract
Staphylococcus aureus (S. aureus) is an important etiological organism in chronic and subclinical mastitis in lactating cows. Given the fundamental role the primary bovine mammary epithelial cells (pBMECs) play as a major first line of defense against invading pathogens, their interactions with S. aureus was hypothesized to be crucial to the establishment of the latter’s infection process. This hypothesis was tested by investigating the global transcriptional responses of pBMECs to three S. aureus strains (S56,S178 and S36) with different virulent factors, using a tag-based high-throughput transcriptome sequencing technique. Approximately 4.9 million total sequence tags were obtained from each of the three S. aureus-infected libraries and the control library. Referenced to the control, 1720, 219, and 427 differentially expressed unique genes were identified in the pBMECs infected with S56, S178 and S36 S. aureus strains respectively. Gene ontology (GO) and pathway analysis of the S56-infected pBMECs referenced to those of the control revealed that the differentially expressed genes in S56-infected pBMECs were significantly involved in inflammatory response, cell signalling pathways and apoptosis. In the same vein, the clustered GO terms of the differentially expressed genes of the S178-infected pBMECs were found to comprise immune responses, metabolism transformation, and apoptosis, while those of the S36-infected pBMECs were primarily involved in cell cycle progression and immune responses. Furthermore, fundamental differences were observed in the levels of expression of immune-related genes in response to treatments with the three S. aureus strains. These differences were especially noted for the expression of important pro-inflammatory molecules, including IL-1α, TNF, EFNB1, IL-8, and EGR1. The transcriptional changes associated with cellular signaling and the inflammatory response in this study may reflect different immunomodulatory mechanisms that underlie the interaction between pBMECs and S. aureus strains during infection by the latter.
Highlights
Bovine mastitis–inflammation of the mammary gland–is the most significant disease in dairy cattle with regard to frequency of occurrence, animal welfare, and economic cost, which is estimated to approach $2 billion annually in the US [1,2]
Mastitis threatens the income of farmers and the image of the dairy sector regarding issues related to animal welfare, milk quality and public health, which is of particular concern as the inevitable indiscriminate use of antibiotics in tackling cattle mastitis would eventually result in the irrational exposure of humans to sub-lethal doses of these antibiotic residues through milk consumption, resulting in the worsening of antibiotic-resistance problems associated with antimicrobial chemotherapy in humans [3]
Primary Bovine Mammary Epithelial Cell Culture Fresh milk was collected from eight healthy Holstein cows in mid lactation having no clinical signs of mastitis and excluded its bacterial infection by conducting bacterial test. primary bovine mammary epithelial cells (pBMECs) were isolated from the bacterial-free milk and cultured by following the method described in Danowski et al [25] and Buehring [26]
Summary
Bovine mastitis–inflammation of the mammary gland–is the most significant disease in dairy cattle with regard to frequency of occurrence, animal welfare, and economic cost, which is estimated to approach $2 billion annually in the US [1,2]. S. aureus is a gram-positive pathogenic bacterium, largely responsible for mastitis in humans and cattle [4]. S. aureus infection can result in obvious clinical mastitis, it often evades immune response mechanisms to institute life-long subclinical chronic infections. Aureus infection can result in obvious clinical mastitis, it often evades immune response mechanisms to institute life-long subclinical chronic infections This contributes in no small way to the growing interest in the studies of the involvement of S. aureus in bovine mastitis. Many studies have confirmed its ability to invade and survive in diverse cell types, including mammary epithelial cells, neutrophils, and macrophages [6,7,8]
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