title: Effects of colistin on biofilm matrices of Escherichia coli and Staphylococcus aureus.
abstract: Biofilms are the preferred environment of micro-organisms on various surfaces such as catheters and heart valves, are associated with numerous difficult-to-treat and recurrent infections, and confer an extreme increase in antibiotic tolerance to most compounds. The aim of this study was to evaluate how colistin affects both the extracellular biofilm matrix and the embedded bacteria in biofilms of methicillin-resistant Staphylococcus aureus (MRSA), a species with intrinsic resistance to colistin, and colistin-susceptible Escherichia coli. Biofilms of MRSA and E. coli were treated with different concentrations of colistin. The minimum biofilm eradication concentration (MBEC) and the effectiveness of colistin at reducing the planktonic fraction were defined as the remaining viable bacteria measured as CFU/mL. In addition, biofilm-embedded cells were LIVE/DEAD-stained and were analysed by confocal laser scanning microscopy (CLSM). Quantification of the biofilm CLSM images was conducted using an open-access in-house algorithm (qBA). In contrast to MRSA, E. coli biofilms and planktonic cells were significantly reduced by colistin in a concentration-dependent manner. Nevertheless, colistin has been shown to exert a matrix-reducing effect following treatment both in laboratory strains and clinical isolates of MRSA and E. coli. Because exposure to colistin rapidly triggered the emergence of highly resistant clones, monotherapy with colistin should be applied with caution. These results suggest that colistin destabilises the biofilm matrix structure even in species with intrinsic colistin resistance, such as S. aureus, leading to the release of planktonic cells that are more susceptible to antibiotics.
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany. Electronic address: Mareike.Klinger@med.uni-jena.de.
authors.forename: Mareike
authors.initials: M
authors.lastname: Klinger-Strobel
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; InfectoGnostics Research Campus, Philosophenweg 7, 07743 Jena, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Stein
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; Department of Medicine I, Division of Infectious Diseases and Tropical Medicine, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria.
authors.forename: Christina
authors.initials: C
authors.lastname: Forstner
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; InfectoGnostics Research Campus, Philosophenweg 7, 07743 Jena, Germany.
authors.forename: Oliwia
authors.initials: O
authors.lastname: Makarewicz
authors.affiliation: Center for Infectious Diseases and Infection Control, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; InfectoGnostics Research Campus, Philosophenweg 7, 07743 Jena, Germany.
authors.forename: Mathias W
authors.initials: MW
authors.lastname: Pletz
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects*; D003091:Colistin / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology*; D004927:Escherichia coli Infections / Q000382:microbiology; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology*; D050296:Microbial Viability / Q000187:drug effects; D018613:Microscopy, Confocal; D013194:Staining and Labeling; D013203:Staphylococcal Infections / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D003091:Colistin
keywords: Antibiotic resistance; Biofilm quantification; Combined antibiotic treatment; MRSA; Nosocomial infection; Polymyxin