title: Effects of growth in the presence of subinhibitory concentrations of dicloxacillin on Staphylococcus epidermidis and Staphylococcus haemolyticus biofilms.
abstract: Low concentrations of antibiotics can inhibit microbial adherence to medical device surfaces. However, little is known about the changes that occur in the physiology of bacteria within biofilms formed in the presence of subinhibitory (sub-MIC) concentrations of antibiotics. In this study, the densities and matrix compositions of biofilms formed by two coagulase-negative Staphylococcus species in the absence and in the presence of sub-MIC concentrations of dicloxacillin were evaluated. Biofilms formed in the presence of sub-MIC concentrations of dicloxacillin contained less biomass, and there were notable changes in the composition of the biofilm matrix. Changes in the spatial structure were also verified by confocal scanning laser microscopy, indicating that biofilms grown in the presence of sub-MIC concentrations of dicloxicilln had a lower cell density. Physiological alterations in the bacteria within biofilms grown in the presence of subinhibitory concentrations of the antibiotic were also evaluated. The results showed that there were differences in bacterial surface characteristics when cultures were grown in the presence of sub-MIC concentrations of dicloxacillin, including decreased hydrophobicity and decreased expression of the exopolysaccharide poly-N-acetylglucosamine. The elemental composition of the cell surface was also analyzed, and whereas in Staphylococcus epidermidis there were decreases in the oxygen and nitrogen contents, in Staphylococcus haemolyticus there were increases in these two parameters. Additionally, increases in resistance to several antibiotics were observed for the cells within biofilms formed in the presence of dicloxacillin.
authors.affiliation: Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710 Braga, Portugal.
authors.forename: Nuno
authors.initials: N
authors.lastname: Cerca
authors.forename: Silvia
authors.initials: S
authors.lastname: Martins
authors.forename: Sanna
authors.initials: S
authors.lastname: Sillankorva
authors.forename: Kimberly K
authors.initials: KK
authors.lastname: Jefferson
authors.forename: Gerald B
authors.initials: GB
authors.lastname: Pier
authors.forename: Rosario
authors.initials: R
authors.lastname: Oliveira
authors.forename: Joana
authors.initials: J
authors.lastname: Azeredo
mesh_terms: D018441:Biofilms; D004009:Dicloxacillin / Q000494:pharmacology*; D007700:Kinetics; D018613:Microscopy, Confocal; D013212:Staphylococcus epidermidis / Q000187:drug effects / Q000254:growth & development* / Q000648:ultrastructure; D041162:Staphylococcus haemolyticus / Q000187:drug effects / Q000254:growth & development* / Q000648:ultrastructure
chemical_list: D004009:Dicloxacillin