A mathematical model of the link between growth and L-malic acid consumption for five strains of Oenococcus oeni

In winemaking, after the alcoholic fermentation of red wines and some white wines, L-malic acid must be converted into L-lactic acid to reduce the acidity. This malolactic fermentation (MLF) is usually carried out by the lactic acid bacteria Oenococcus oeni. Depending on the level of process control, selected O. oeni is inoculated or the natural microbiota of the cellar is used. This study considers the link between growth and MLF for five strains of O. oeni species. The kinetics of growth and L-malic acid consumption were followed in modified MRS medium (20 °C, pH 3.5, and 10 % ethanol) in anaerobic conditions. A large variability was found among the strains for both their growth and their consumption of L-malic acid. There was no direct link between biomass productivities and consumption of L-malic acid among strains but there was a link of proportionality between the specific growth of a strain and its specific consumption of L-malic acid. Experiments with and without malic acid clearly demonstrated that malic acid consumption improved the growth of strains. This link was quantified by a mathematical model comparing the intrinsic malic acid consumption capacity of the strains

An outbreak in intravenous drug users due to USA300 Latin-American variant community-acquired methicillin-resistant Staphylococcus aureus in France as early as 2007

International audienceIntravenous drug users are at increased risk of Staphylococcus aureus infections. Most cases are related to clones prevalent in the community. We report an outbreak of community-acquired methicillin-resistant Staphylococcus aureus infections that occurred from 2007 to 2009 in intravenous drug users and their close contacts in Northwestern France. Clinical and molecular investigations suggested that the clones were more similar than those usually isolated in the American continent although none of the patients traveled abroad or had contact with individuals who had traveled to the Americas. Then, a retrospective whole genome sequencing and phylogenetic analyses demonstrated that the strains isolated from the first case belong to the USA300 Latin-American variant clone, based on the absence of arginine catabolic mobile element (ACME), and the presence of copper and mercury resistance mobile element (COMER), a distinctive feature of the South American variant. Our study shows genetic evidence for introduction of this clone as early as 2007 in France. This report also illustrates the importance of genome sequencing to finely characterize and monitor the emergence of unexpected S. aureus clones among high-risk populations, especially when living in promiscuity