title: Survival of adhering staphylococci during exposure to a quaternary ammonium compound evaluated by using atomic force microscopy imaging.
abstract: Effects of a quaternary ammonium compound (QAC) on the survival of adhering staphylococci on a surface were investigated using atomic force microscopy (AFM). Four strains with different minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) for the QAC were exposed to three different concentrations of the QAC in potassium phosphate buffer (0.5×, 1×, and 2× MBC) while adhering to glass. Adhering staphylococci were repeatedly imaged with AFM in the contact mode, and the cell surface was found to wrinkle upon progressive exposure to the QAC until bacteria disappeared from the substratum. Higher concentrations of QAC yielded faster wrinkling and the disappearance of bacteria during imaging. Two slime-producing staphylococcal strains survived longer on the surface than two non-slime-producing strains despite similar MICs and MBCs. All staphylococci adhering in unscanned areas remained adhering during exposure to QAC. Since MICs and MBCs did not relate to bacterial cell surface hydrophobicities and zeta potentials, survival on the surface is probably not determined by the direct interaction of QAC molecules with the cell surface. Instead, it is suggested that the pressure of the AFM tip assists the incorporation of QAC molecules in the membrane and enhances their bactericidal efficacy. In addition, the prolonged survival under pressure from slime-producing strains on a surface may point to a new protective role of slime as a stress absorber, impeding the incorporation of QAC molecules. The addition of Ca(2+) ions to a QAC solution yielded longer survival of intact, adhering staphylococci, suggesting that Ca(2+) ions can impede the exchange of membrane Ca(2+) ions required for QAC incorporation.
authors.affiliation: Department of Biomedical Engineering FB-40, WJ Kolff Institute, University Medical Center Groningen and University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Crismaru
authors.forename: Lia A T W
authors.initials: LA
authors.lastname: Asri
authors.forename: Ton J A
authors.initials: TJ
authors.lastname: Loontjens
authors.forename: Bastiaan P
authors.initials: BP
authors.lastname: Krom
authors.forename: Joop
authors.initials: J
authors.lastname: de Vries
authors.forename: Henny C
authors.initials: HC
authors.lastname: van der Mei
authors.forename: Henk J
authors.initials: HJ
authors.lastname: Busscher
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D018625:Microscopy, Atomic Force / Q000379:methods*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D013210:Staphylococcus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D000644:Quaternary Ammonium Compounds; D002118:Calcium