Yves Le Loir

Yves Le Loir

French National Institute for Agricultural Research, France

Title: Staphylococcus aureus and ruminant mastitis: staphylococcal factors involved in the infection acuteness and ecological factors modulating virulence expression in the mammary context


Yves Le Loir is a research scientist at INRA (French National Institute for Agricultural Research). He originally studied biochemistry (University of Rennes, France) and agriculture (ENSA-Agrocampus Ouest, France). He completed his Ph.D. (University of Paris XI) in microbiology on heterologous protein secretion in Lactococcus lactis, the model lactic acid bacterium (LAB). His current works are focused on host adaptation (ruminants) in Staphylococcus aureus and interactions between S. aureus and LAB. He has co-authored 70 peer-reviewed papers and book chapters. He is deputy director of the STLO Unit in Rennes, France.


Staphylococcus aureus is a major pathogen involved in ruminant mastitis. Staphylococcal mastitis is remarkably variable in terms of severity ranging from subclinical to gangrenous manifestations. It is also prone to recurrence partly because of S. aureus ability to invade mammary epithelial cells (MEC). We investigate what makes a strain more or less virulent by identifying staphylococcal factors involved in mastitis acuteness. We also take account of ecological factors (udder ecosystem) that may modulate S. aureus virulence expression. S. aureus strains isolated from gangrenous (O11) or subclinical (O46) ewe mastitis, were selected for identifying potential factors involved in mastitis acuteness. Despite a close phylogenetic relationship, these two strains reproducibly induce severe (O11) or mild (O46) symptoms in experimental ewe mastitis. Using a comprehensive omic characterization (genome, transcriptome, proteome and seroproteome), we showed dramatic differences between O11 and O46 relying on their ability to adapt and express virulence in a mammary context. The exact role of the genes identified here (exoproteins, mobile genetic elements, iron metabolism), and likely involved in mastitis acuteness and pathogen-host interactions, remains to be determined. Besides, we investigated the inhibitory potential of the lactic acid bacterium, Lactobacillus casei, naturally present in the teat ecosystem, against invasion of MEC by ruminant S. aureus isolates. Our results indicated L. casei strains impaired, in a contact- dependent way, adhesion and internalization of S. aureus without altering viability of MEC. Altogether, these results open avenues for the development of prevention strategies against mastitis.

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