title: Biofilm deficiency in polysaccharide intercellular adhesin-negative variants of Staphylococcus epidermidis selected by subminimal inhibitory concentrations of gentamicin.
abstract: Staphylococcus epidermidis is a cause of orthopedic device-related infection, and to treat such infection, biofilms should be controlled. Polysaccharide intercellular adhesin (PIA) is associated with the biofilm-forming ability of staphylococcal strains. PIA in biofilm-positive staphylococcal strains can be detected by the Congo red agar (CRA) method. In this study, we used the CRA method to examine the effects of subminimal inhibitory concentrations (sub-MICs) of 11 antibacterial agents on PIA production by S. epidermidis. We found that the PIA-negative variants were selected only by sub-MICs of gentamicin (GM). This PIA-negative phenotype was maintained over several generations in the absence of GM. Such selection occurred in six of eight clinical isolates, as well as in the biofilm-positive control strain. No such selection occurred with aminoglycoside antibiotics except for GM. Most of the PIA-negative variants that were selected by GM showed a markedly lower biofilm-forming ability on stainless steel washers than their untreated parent strains. In conclusion, variants with lower biofilm-forming ability may be selected by a sub-MIC of GM. Investigation of the reason why variants with reduced biofilm-forming ability can be selected in the presence of sub-MICs of GM may contribute to strategies against biofilm-related infections.
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Biomedical Science, Nagasaki University, Nagasaki 852-8501, Japan. t.tamai@ind.bbiq.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Tamai
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Tsurumoto
authors.forename: Shiro
authors.initials: S
authors.lastname: Kajiyama
authors.forename: Shinji
authors.initials: S
authors.lastname: Adachi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Sakimura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Shindo
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001422:Bacterial Adhesion; D018441:Biofilms; D003224:Congo Red / Q000378:metabolism; D005839:Gentamicins / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests / Q000379:methods; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D013212:Staphylococcus epidermidis / Q000187:drug effects* / Q000502:physiology
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins; D011135:Polysaccharides, Bacterial; C113579:polysaccharide intercellular adhesin; D003224:Congo Red