title: Importance of the Exopolysaccharide Matrix in Antimicrobial Tolerance of Pseudomonas aeruginosa Aggregates.
abstract: Pseudomonas aeruginosais an opportunistic pathogen that can infect the lungs of cystic fibrosis (CF) patients and persist in the form of antibiotic-tolerant aggregates in the mucus. It has recently been suggested that such aggregates are formed due to restricted bacterial motility independent of the production of extracellular matrix components, and that they do not rely on an extracellular matrix for antimicrobial tolerance. However, we show here that biofilm matrix overexpression, as displayed by various clinical isolates, significantly protectsP. aeruginosaaggregates against antimicrobial treatment. Alginate-overproducingmucAmutant bacteria growing in aggregates showed highly increased antibiotic tolerance compared to wild-type bacteria in aggregates. Deletion ofalgDin themucAmutant strain abrogated alginate production and reversed the antibiotic tolerance displayed by the aggregates to a level similar to that observed for aggregates formed by the wild type. TheP. aeruginosaΔwspFand ΔyfiRmutant strains both overproduce Pel and Psl exopolysaccharide, and when these bacteria grew in aggregates, they showed highly increased antibiotic tolerance compared to wild-type bacteria growing in aggregates. However, the ΔwspFand ΔyfiRmutant strains, deficient in Pel/Psl production due to additional ΔpelAΔpslBCDdeletions, formed aggregates that displayed antibiotic tolerance levels close to those of wild-type aggregates. These results suggest that biofilm matrix components, such as alginate, Pel, and Psl, do play a role in the tolerance toward antimicrobials when bacteria grow as aggregates.
authors.affiliation: Costerton Biofilm Center, Department of Immunology and Microbiology, University of Copenhagen, Copenhagen N, Denmark.
authors.forename: Lise
authors.initials: L
authors.lastname: Goltermann
authors.affiliation: Costerton Biofilm Center, Department of Immunology and Microbiology, University of Copenhagen, Copenhagen N, Denmark ttn@sund.ku.dk.
authors.forename: Tim
authors.identifier: 0000-0002-9751-474X
authors.initials: T
authors.lastname: Tolker-Nielsen
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000187:drug effects; D005109:Extracellular Matrix / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008826:Microbial Sensitivity Tests; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial
keywords: aggregates; antimicrobial tolerance; biofilm; extracellular matrix