The Impact of Mastitis on the Biochemical Parameters, Oxidative and Nitrosative Stress Markers in Goat's Milk: A Review

Goat mastitis has become one of the most frequently diagnosed conditions in goat farms, with significant economic impact on the dairy industry. Inflammation of the mammary gland poses serious consequences on milk composition, with changes regarding biochemical parameters and oxidative stress markers. The aim of this paper is to present the most recent knowledge on the main biochemical changes that occur in the mastitic milk, as well as the overall effect of the oxidative and nitrosative stress on milk components, focusing on both enzymatic and nonenzymatic antioxidant markers. Mastitis in goats is responsible for a decrease in milk production, change in protein content with pronounced casein hydrolysis, and reduction in lactose concentration and milk fat. Milk enzymatic activity also undergoes changes, regarding indigenous enzymes and those involved in milk synthesis. Furthermore, during mastitis, both the electrical conductivity and the milk somatic cell count are increased. Intramammary infections are associated with a reduced milk antioxidant capacity and changes in catalase, lactoperoxidase, glutathione peroxidase or superoxide dismutase activity, as well as reduced antioxidant vitamin content. Mastitis is also correlated with an increase in the concentration of nitric oxide, nitrite, nitrate and other oxidation compounds, leading to the occurrence of nitrosative stress.

Determination of changes in bovine plasma and milk proteins during naturally occurring Escherichia coli mastitis by comparative proteomic analysis

The aim of this study was to investigate changes in plasma and milk proteins in response to Escherichia coli infection in cows. Plasma and milk were collected from healthy cows, cows suffering from mild E. coli mastitis, and cows suffering from severe E. coli mastitis. Protein composition was examined by two-dimensional gel electrophoresis coupled with mass spectrometry. Plasma haptoglobin and α-1 acid glycoprotein demonstrated greater expression in mastitic cows compared with controls, but there were no difference between mildly and severely mastitic cows. Milk from mildly mastitic cows showed increased albumin and casein variants. Severely mastitic cows showed lower casein levels and increased anti-microbial and acute phase proteins. Milk α-1 acid glycoprotein and cathelicidins were associated with severe mastitis. A greater number of β-casein fragments that corresponded to β-casein isoforms were found in milk from mildly mastitic cows. These results suggest that caseins levels decreased and the concentrations of anti-microbial and acute phase proteins increased corresponding to the degree of E. coli mastitis. Nevertheless, further studies are needed to determine whether cathelicidin could serve as a diagnostic marker for mastitis.

Casein breakdown in bovine milk by a field strain of Staphylococcus aureus

The objectives of this study were to establish the proteolytic effects of Staphylococcus aureus during mastitis on economically important milk proteins. Concentrations of milk proteins were determined by capillary electrophoresis in an experimental model using a field strain of S. aureus. The pathogen was inoculated into bacteria-free control milk to imitate proteolysis caused by the pathogen in the mammary gland between milkings. Milk content of caseins (CN) α(S1), α(S2), κ, β(A1), and β(A2) and whey proteins α-lactalbumin and β-lactoglobulin were analyzed initially and after 6 h of incubation. After 6 h, the overall CN content was significantly reduced (21%) in milk inoculated with S. aureus compared with the bacteria-free control milk. S. aureus significantly lowered concentration of α(S1)-CN (2.5%), β(A1)-CN (3%), and β(A2)-CN (5%). S. aureus also hydrolyzed κ-CN into para-κ-CN, with significant reduction of κ-CN (7.4%) as a consequence.

Protein degradation in bovine milk caused byStreptococcus agalactiae

Streptococcus(Str.)agalactiaeis a contagious mastitis bacterium, often associated with cases of subclinical mastitis. Different mastitis bacteria have been evaluated previously from a diagnostic point of view, but there is a lack of knowledge concerning their effect on milk composition. Protein composition is important in achieving optimal yield and texture when milk is processed to fermented products, such as cheese and yoghurt, and is thus of great economic value. The aim of thisin vitrostudy was to evaluate protein degradation mainly caused by exogenous proteases originating from naturally occurringStr. agalactiae. The samples were incubated at 37°C to imitate degradation caused by the bacteria in the udder. Protein degradation caused by different strains ofStr. agalactiaewas also investigated. Protein degradation was observed to occur whenStr. agalactiaewas added to milk, but there were variations between strains of the bacteria. Caseins, the most economically important proteins in milk, were degraded up to 75% in milk inoculated withStr. agalactiaein relation to sterile ultra-high temperature (UHT) milk, used as control milk. The major whey proteins, α-lactalbumin and β-lactoglobulin, were degraded up to 21% in relation to the sterile control milk. These results suggest that different mastitis bacteria but also different strains of mastitis bacteria should be evaluated from a milk quality perspective to gain knowledge about their ability to degrade the economically important proteins in milk.

First evidence of the presence of genomic islands in Escherichia coli P4, a mammary pathogen frequently used to induce experimental mastitis

Mastitis pathogens belonging to Escherichia coli species are often considered as environmental opportunistic pathogens that invade the udder and are rapidly killed by the immune system of cows. However, several studies have reported that some of these strains are able to persist in the udder for prolonged periods or to adhere and invade mammary epithelial cells, suggesting that they might possess some specific properties or genes that could be involved in their capacity to provoke mastitis. The aim of this work was to search for such specific genes in the E. coli strain P4, which was isolated from a case of severe mastitis and is often used to induce experimental mastitis. We established that this strain belongs to phylogenetic group A of the E. coli species, and that its core genome is very similar to that of the commensal nonpathogenic strain E. coli K-12 MG1655. Seventeen transfer RNA loci, known to be frequently associated with genomic islands, were screened and an altered structure was detected for 7 of them. The partial characterization of 5 of these loci (asnT, leuX, pheV, serU, and thrW) and the complete characterization of 1 (argW) revealed the presence of genomic islands that differ from those already described in pathogenic or nonpathogenic E. coli strains.