Abstract
Intramammary infection leading to bovine mastitis is the leading disease problem affecting dairy cows and has marked effects on the milk produced by infected udder quarters. An experimental model of Streptococcus uberis mastitis has previously been investigated for clinical, immunological and pathophysiological alteration in milk, and has been the subject of peptidomic and quantitative proteomic investigation. The same sample set has now been investigated with a metabolomics approach using liquid chromatography and mass spectrometry. The analysis revealed over 3000 chromatographic peaks, of which 690 were putatively annotated with a metabolite. Hierarchical clustering analysis and principal component analysis demonstrated that metabolite changes due to S. uberis infection were maximal at 81 hours post challenge with metabolites in the milk from the resolution phase at 312 hours post challenge being closest to the pre-challenge samples. Metabolic pathway analysis revealed that the majority of the metabolites mapped to carbohydrate and nucleotide metabolism show a decreasing trend in concentration up to 81 hours post-challenge whereas an increasing trend was found in lipid metabolites and di-, tri- and tetra-peptides up to the same time point. The increase in these peptides coincides with an increase in larger peptides found in the previous peptidomic analysis and is likely to be due to protease degradation of milk proteins. Components of bile acid metabolism, linked to the FXR pathway regulating inflammation, were also increased. Metabolomic analysis of the response in milk during mastitis provides an essential component to the full understanding of the mammary gland's response to infection.
Highlights
Intramammary infection leading to bovine mastitis is the leading disease problem affecting dairy cows and has marked effects on the milk produced by infected udder quarters
This paper reports a metabolomics investigation of an experimental model of Streptococcus uberis mastitis, adding to previous studies which have examined the pathophysiology of the immunological responses,[1] the protein changes in the acute phase reaction along with the omic investigation of the peptidome[2] and the system-wide quantitative proteomic analysis.[3]
There has been no previous report of metabolomics profiling of milk during mastitis using a Liquid Chromatography Mass Spectrometry (LC-MS) approach
Summary
Intramammary infection leading to bovine mastitis is the leading disease problem affecting dairy cows and has marked effects on the milk produced by infected udder quarters. Compared with NMR spectroscopy or GC-MS, LC-MS has the potential to analyse a larger proportion of the metabolome due to its high sensitivity.[7] we used a LC-MS method to quantify temporal changes in metabolite concentrations in milk during mastitis in an experimental model of the disease The aim of this part of the overall investigation was to assess the variation in the metabolome in bovine milk samples following progression of the experimental intramammary challenge with a host-adapted strain of Streptococcus uberis (FSL Z1-048).[1] S. uberis represents an important cause of mastitis in dairies in the UK and it has been shown to cause severe disease which is often difficult to control.[18] The goal of the metabolomics analysis was to identify the metabolites that demonstrated either an increase or decrease in milk from infected udder quarters over a time course from preinfection to resolution. This would provide a better understanding of metabolic pathways altered in mastitis, and along with the results of the immunological, acute phase, peptidomic and proteomic investigations provide a novel insight into the bacterial IMI and the host response
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