Biofilm deficiency in polysaccharide intercellular adhesin-negative variants of staphylococcus epidermidis selected by subminimal inhibitory concentrations of gentamicin

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 biofilmforming 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

Effect of Vancomycin and Glucose on Biofilm Formation by Coagulase-negative Staphylococci: Investigation of Standard Strains and Clinical Strains isolated from Implant-related Infection

[Objective] The objective of this study was to investigate the suppressive effect of antibiotics and presence or absence of glucose on biofilm formation on metal surfaces by coagulase-negative Staphylococci. [Materials and Methods] Bacterial strains included a standard biofilm-forming strain of Staphylococcus epidermidis, nonbiofilm-forming strain of Staphylococcus hominis, and two clinical strains of Staphylococcus epidermidis isolated from implantrelatedinfection (IRI). Vancomycin (VCM) was used as the antibiotic. Trypticase soy broth (TSB) and TSB without dextrose (TSB w/o D) were used as growth media. Each strain was adhered to stainless steel washers and cultured in different growth media with various VCM concentrations for different lengths of time. The degree of biofilm formation was measured as the biofilm coverage rate (BCR). [Results] BCR decreased with increasing VCM concentration and shorter incubation time; however, the degree of suppression varied by strain. BCR was lower for strains cultured in TSB w/o D than for those in TSB. BCR for 8-h incubation group was significantly reduced at lower VCM concentrations in TSB w/o D than in TSB. [Conclusions] Biofilm formation was suppressed in absence of glucose environments, suggesting the importance of controlling blood glucose levels during the perioperative period to prevent IRI

Effect of Vancomycin and Glucose on Biofilm Formation by Coagulase-negative Staphylococci: Investigation of Standard Strains and Clinical Strains isolated from Implant-related Infection

[Objective] The objective of this study was to investigate the suppressive effect of antibiotics and presence or absence of glucose on biofilm formation on metal surfaces by coagulase-negative Staphylococci. [Materials and Methods] Bacterial strains included a standard biofilm-forming strain of Staphylococcus epidermidis, nonbiofilm-forming strain of Staphylococcus hominis, and two clinical strains of Staphylococcus epidermidis isolated from implantrelated infection (IRI). Vancomycin (VCM) was used as the antibiotic. Trypticase soy broth (TSB) and TSB without dextrose (TSB w/o D) were used as growth media. Each strain was adhered to stainless steel washers and cultured in different growth media with various VCM concentrations for different lengths of time. The degree of biofilm formation was measured as the biofilm coverage rate (BCR). [Results] BCR decreased with increasing VCM concentration and shorter incubation time; however, the degree of suppression varied by strain. BCR was lower for strains cultured in TSB w/o D than for those in TSB. BCR for 8-h incubation group was significantly reduced at lower VCM concentrations in TSB w/o D than in TSB. [Conclusions] Biofilm formation was suppressed in absence of glucose environments, suggesting the importance of controlling blood glucose levels during the perioperative period to prevent IRI

Biofilm-Forming Staphylococcus epidermidis Expressing Vancomycin Resistance Early after Adhesion to a Metal Surface

We investigated biofilm formation and time of vancomycin (VCM) resistance expression after adhesion to a metal surface in Staphylococcus epidermidis. Biofilm-forming Staphylococcus epidermidis with a VCM MIC of 1 μg/mL was used. The bacteria were made to adhere to a stainless steel washer and treated with VCM at different times and concentrations. VCM was administered 0, 2, 4, and 8 hours after adhesion. The amount of biofilm formed was evaluated based on the biofilm coverage rates (BCRs) before and after VCM administration, bacterial viability in biofilm was visually observed using the fluorescence staining method, and the viable bacterial count in biofilm was measured. The VCM concentration required to decrease BCR significantly compared with that of VCM-untreated bacteria was 4 μg/mL, even in the 0 hr group. In the 4 and 8 hr groups, VCM could not inhibit biofilm growth even at 1,024 μg/mL. In the 8 hr group, viable bacteria remained in biofilm at a count of 104 CFU even at a high VCM concentration (1,024 μg/mL). It was suggested that biofilm-forming Staphylococcus epidermidis expresses resistance to VCM early after adhesion to a metal surface. Resistance increased over time after adhesion as the biofilm formed, and strong resistance was expressed 4–8 hours after adhesion