title: Planktonic aggregates of Staphylococcus aureus protect against common antibiotics.
abstract: Bacterial cells are mostly studied during planktonic growth although in their natural habitats they are often found in communities such as biofilms with dramatically different physiological properties. We have examined another type of community namely cellular aggregates observed in strains of the human pathogen Staphylococcus aureus. By laser-diffraction particle-size analysis (LDA) we show, for strains forming visible aggregates, that the aggregation starts already in the early exponential growth phase and proceeds until post-exponential phase where more than 90% of the population is part of the aggregate community. Similar to some types of biofilm, the structural component of S. aureus aggregates is the polysaccharide intercellular adhesin (PIA). Importantly, PIA production correlates with the level of aggregation whether altered through mutations or exposure to sub-inhibitory concentrations of selected antibiotics. While some properties of aggregates resemble those of biofilms including increased mutation frequency and survival during antibiotic treatment, aggregated cells displayed higher metabolic activity than planktonic cells or cells in biofilm. Thus, our data indicate that the properties of cells in aggregates differ in some aspects from those in biofilms. It is generally accepted that the biofilm life style protects pathogens against antibiotics and the hostile environment of the host. We speculate that in aggregate communities S. aureus increases its tolerance to hazardous environments and that the combination of a biofilm-like environment with mobility has substantial practical and clinical importance.
authors: Department of Veterinary Disease Biology, University of Copenhagen, Frederiksberg, Denmark.
authors: Jakob
authors: J
authors: Haaber
authors: Marianne Thorup
authors: MT
authors: Cohn
authors: Dorte
authors: D
authors: Frees
authors: Thorbjørn Joest
authors: TJ
authors: Andersen
authors: Hanne
authors: H
authors: Ingmer
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D018441:Biofilms; D004252:DNA Mutational Analysis; D007834:Lasers; D008164:Luminescent Proteins / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008855:Microscopy, Electron, Scanning / Q000379:methods; D009154:Mutation; D010316:Particle Size; D010933:Plankton / Q000235:genetics* / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D013234:Stem Cells
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D008164:Luminescent Proteins; D011134:Polysaccharides; C054562:yellow fluorescent protein, Bacteria