Abstract
BackgroundS. aureus is one of the main pathogens responsible for the intra-mammary infection in dairy ruminants. Although much work has been carried out to understand the complex physiological and cellular events that occur in the mammary gland in response to S. aureus, the protective mechanisms are still poorly understood. The objectives of the present study were to investigate gene expression during the early response of the goat mammary gland to an experimental challenge with S. aureus, in order to better understand the local and systemic response and to compare them in two divergent lines of goat selected for high and low milk somatic cell scores.ResultsNo differences in gene expression were found between high and low SCS (Somatic Cells Score) selection lines. Analysing the two groups together, an expression of 300 genes were found to change from T0 before infection, and T4 at 24 hours and T5 at 30 hours following challenge. In blood derived white blood cells 8 genes showed increased expression between T0 and T5 and 1 gene has reduced expression. The genes showing the greatest increase in expression following challenge (5.65 to 3.16 fold change) play an important role in (i) immune and inflammatory response (NFKB1, TNFAIP6, BASP1, IRF1, PLEK, BATF3); (ii) the regulation of innate resistance to pathogens (PTX3); and (iii) the regulation of cell metabolism (CYTH4, SLC2A6, ARG2). The genes with reduced expression (−1.5 to −2.5 fold) included genes involved in (i) lipid metabolism (ABCG2, FASN), (ii) chemokine, cytokine and intracellular signalling (SPPI), and (iii) cell cytoskeleton and extracellular matrix (KRT19).ConclusionsAnalysis of genes with differential expression following infection showed an inverse relationship between immune response and lipid metabolism in the early response of the mammary gland to the S. aureus challenge. PTX3 showed a large change in expression in both milk and blood, and is therefore a candidate for further studies on immune response associated with mastitis.
Highlights
S. aureus is one of the main pathogens responsible for the intra-mammary infection in dairy ruminants
S. aureus present in milk samples reached a maximum at 18h post-infection with a mean of 5.8 log10 CFU/ml (Colony Forming Unit/ml) in the Low SCS (LSCS) line animals and 6.1 log10 CFU/ml the High SCS (HSCS) selection line goats
Strain analysis using the RAPD-PCR (Randomly Amplified Polymorphic DNA-PCR) method confirmed that S. aureus isolated from infected udders were the same as the strain used for the infection
Summary
S. aureus is one of the main pathogens responsible for the intra-mammary infection in dairy ruminants. Previous analyses have been focused on effector mechanisms in later stages of the adaptive immune response to an infection [10], studies of the early phases of infection which could shed light on innate defence mechanisms process in the udder are currently missing. Such studies can only be achieved in controlled infection experiments where the time of infection and pathogen involved are known
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