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Press Info item.
21/07/2011
A major step towards the control of mastitis
Intramammary infections, commonly referred to as mastitis, are the principal cause of economic losses in dairy production. Different pathogenic agents cause these infections, but Staphylococcus aureus is one of the most common and the most difficult to control. Using an innovative technique, researchers from INRA and ANSES (1) have, for the first time, been able to identify the proteins in this bacterium that trigger an immune response during mastitis in sheep. They have also identified proteins that are specifically produced by pathogenic strains causing mild or severe mastitis. These findings will enable a clearer understanding of the infective process of Staphylococcus and then make it possible to discover new weak points in this bacterium.
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Mastitis is a major problem for sheep, cattle and goat farmers in terms of economic losses, veterinary costs and additional workload. In cattle, the worldwide economic losses linked to mastitis have been evaluated at approximately €5000 per year and per herd of 100 cows. Mastitis can be extremely virulent, causing gangrene of the udder and leading to the animal's death. It may also be more moderate, and even develop undetected. It all depends on the infective strain, as well as factors such as the health status of the animals, their age or their susceptibility to pathogens. When mastitis is caused by the bacterium Staphylococcus aureus, antibiotic therapy is often ineffective, and recurrences in previously infected animals are common. The vaccines available at present only display limited efficacy in controlling this pathogen.
That is why the researchers wanted to determine the proteins in staphylococci that trigger an immune response. To achieve this, they employed an innovative technique called SERPA (SERological Proteome Analysis), originally developed to identify new cancer markers in humans. This method consists in revealing all the proteins present in the pathogen, obtained by bacterial culture, and the antibodies present in the blood of infected ewes.
The team performed these analyses on two strains of S. aureus, one highly virulent (O11), and the other mildly virulent (O46). For the first time, they were thus able to identify 89 proteins in Staphylococcus aureus that reacted with the immune system of sheep.
Of these 89 proteins, 52 had already been described in other types of infections affecting other organisms (humans, rats or cows). However, it was not previously known that the 37 others constituted antigens capable of triggering an immune response in ruminants. This opens new perspectives for the control of S. aureus, and notably the development of a future vaccine. But that is not all: the scientists also showed that among these 89 proteins, twelve were specific to the virulent strain O11 and three were specific to the milder strain O46. These specific proteins proved to be excellent markers to recognise the different strains and monitor the most aggressive.
Furthermore, the research team has already started to focus on the function of the proteins revealed. They have thus identified proteins for stress resistance, and proteins for the metabolism of iron and toxins. This will allow them to better understand the infective strategies implemented by Staphylococcus aureus, as well as the stresses and deficiencies it must overcome to develop in udders and cause mastitis. The study of host-pathogen relationships generated by this work will enable the determination of new targets that can be attacked in S. aureus, and the development of novel therapeutic strategies and new preventive measures.
(1) ANSES: French National Agency for Health Safety.
Reference:
Staphylococcus aureus seroproteomes discriminate ruminant isolates causing mild or severe mastitis.
Caroline Le Maréchal, Julien Jardin, Gwenaël Jan, Sergine Even, Coralie Pulido, Jean-Michel Guibert, David Hernandez, Patrice François, Jacques Schrenzel, Dieter Demon, Evelyne Meyer, Nadia Berkova, Richard Thiéry, Eric Vautor, et Yves Le Loir.
Veterinary Research. 42(1):35; doi:10.1186/1297-9716-42-35
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