title: Staphylococcus aureus virulence and metabolism are dramatically affected by Lactococcus lactis in cheese matrix.
abstract: In complex environments such as cheeses, the lack of relevant information on the physiology and virulence expression of pathogenic bacteria and the impact of endogenous microbiota has hindered progress in risk assessment and control. Here, we investigated the behaviour of Staphylococcus aureus, a major foodborne pathogen, in a cheese matrix, either alone or in the presence of Lactococcus lactis, as a dominant species of cheese ecosystems. The dynamics of S. aureus was explored in situ by coupling a microbiological and, for the first time, a transcriptomic approach. Lactococcus lactis affected the carbohydrate and nitrogen metabolisms and the stress response of S. aureus by acidifying, proteolysing and decreasing the redox potential of the cheese matrix. Enterotoxin expression was positively or negatively modulated by both L. lactis and the cheese matrix itself, depending on the enterotoxin type. Among the main enterotoxins involved in staphylococcal food poisoning, sea expression was slightly favoured in the presence of L. lactis, whereas a strong repression of sec4 was observed in cheese matrix, even in the absence of L. lactis, and correlated with a reduced saeRS expression. Remarkably, the agr system was downregulated by the presence of L. lactis, in part because of the decrease in pH. This study highlights the intimate link between environment, metabolism and virulence, as illustrated by the influence of the cheese matrix context, including the presence of L. lactis, on two major virulence regulators, the agr system and saeRS.
authors.affiliation: INRA, UMR1253 STLO, 85 rue de Saint Brieuc, F-35000 Rennes, France. Agrocampus Ouest, UMR1253 STLO, 85 rue de Saint Brieuc, F-35000 Rennes, France. Université de Toulouse; INSA, UPS, INP; LISBP, 135 Avenue de Rangueil, F-31077 Toulouse, France. INRA, UMR792 Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France. CNRS, UMR5504, F-31400 Toulouse, France. Genomic Research Laboratory, University of Geneva Hospitals, Rue Gabrielle-Perret-Gentil, 4 CH-1211 Geneva 14, Switzerland. University Medical Center, Department of Microbiology and Molecular Medicine, CH-1211 Geneva 4, Switzerland. Laboratory for Study and Research on Quality of Food and on Food Processes, French Agency for Food Safety (AFSSA-lerqap), National and Community Reference Laboratory, 94704 Maisons-Alfort cedex, France.
authors.forename: Marina
authors.initials: M
authors.lastname: Cretenet
authors.forename: Sébastien
authors.initials: S
authors.lastname: Nouaille
authors.forename: Jennifer
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authors.lastname: Thouin
authors.forename: Lucie
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authors.lastname: Rault
authors.forename: Ludwig
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authors.lastname: Stenz
authors.forename: Patrice
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authors.lastname: François
authors.forename: Jacques-Antoine
authors.initials: JA
authors.lastname: Hennekinne
authors.forename: Michel
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authors.lastname: Piot
authors.forename: Marie Bernadette
authors.initials: MB
authors.lastname: Maillard
authors.forename: Jacques
authors.initials: J
authors.lastname: Fauquant
authors.forename: Pascal
authors.initials: P
authors.lastname: Loubière
authors.forename: Yves
authors.initials: Y
authors.lastname: Le Loir
authors.forename: Sergine
authors.initials: S
authors.lastname: Even