title: Role of Ionic Strength in Staphylococcal Cell Aggregation.
abstract: Cell aggregation plays a key role in biofilm formation and pathogenesis of Staphylococcus species. Although the molecular basis of aggregation in Staphylococci has already been extensively investigated, the influence of environmental factors, such as ionic strength, remains poorly understood. In this paper, we report a new type of cellular aggregation of Staphylococci that depends solely on ionic strength. Seven strains out of 14, all belonging to staphylococcal species, formed large cell clusters within minutes in buffers of ionic strength ranging from 1.5 to 50 mM, whereas isolates belonging to other Gram-positive species did not display this phenotype. Atomic force microscopy (AFM) with chemically functionalized tips provided direct evidence that ionic strength modulates cell surface adhesive properties through changes in cell surface charge. The optimal ionic strength for aggregation was found to be strain dependent, but in all cases, bacterial aggregates formed at an ionic strength of 1.5-50 mM were rapidly dispersed in a solution of higher ionic strength, indicating a reversibility of the cell aggregation process. These findings suggest that some staphylococcal isolates can respond to ionic strength as an external stimulus to trigger rapid cell aggregation in a way that has not yet been reported.
authors.affiliation: Laboratory of Food and Environmental Microbiology, Applied Microbiology, Earth and Life Institute, ‡Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and §Institute of Life Sciences, Université catholique de Louvain , Croix du Sud 2, L7.05.12, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Vanzieleghem
authors.affiliation: Laboratory of Food and Environmental Microbiology, Applied Microbiology, Earth and Life Institute, ‡Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and §Institute of Life Sciences, Université catholique de Louvain , Croix du Sud 2, L7.05.12, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Numa
authors.initials: N
authors.lastname: Couniot
authors.affiliation: Laboratory of Food and Environmental Microbiology, Applied Microbiology, Earth and Life Institute, ‡Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and §Institute of Life Sciences, Université catholique de Louvain , Croix du Sud 2, L7.05.12, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Philippe
authors.initials: P
authors.lastname: Herman-Bausier
authors.affiliation: Laboratory of Food and Environmental Microbiology, Applied Microbiology, Earth and Life Institute, ‡Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and §Institute of Life Sciences, Université catholique de Louvain , Croix du Sud 2, L7.05.12, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Denis
authors.initials: D
authors.lastname: Flandre
authors.affiliation: Laboratory of Food and Environmental Microbiology, Applied Microbiology, Earth and Life Institute, ‡Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and §Institute of Life Sciences, Université catholique de Louvain , Croix du Sud 2, L7.05.12, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Yves F
authors.initials: YF
authors.lastname: Dufrêne
authors.affiliation: Laboratory of Food and Environmental Microbiology, Applied Microbiology, Earth and Life Institute, ‡Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), and §Institute of Life Sciences, Université catholique de Louvain , Croix du Sud 2, L7.05.12, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: Jacques
authors.initials: J
authors.lastname: Mahillon
mesh_terms: D018625:Microscopy, Atomic Force; D009994:Osmolar Concentration; D013210:Staphylococcus / Q000737:chemistry* / Q000648:ultrastructure