Differential susceptibility of Staphylococcus epidermidis biofilms to vancomycin, daptomycin and linezolid between clinical Isolates from neonates and adults

Abstract This study aimed to compare the effects of vancomycin, linezolid and daptomycin against planktonic cells and biofilms of 32 bloodstream isolates derived from neonates and adults of three hospitals. Staphylococcus epidermidis biofilm formation was spectrophotometrically assessed following safranin staining. Susceptibility testing of planktonic and biofilm cells was performed by XTT reduction assay. MICs of vancomycin and daptomycin were 1mg/L and that of linezolid 0.5 mg/L. At concentrations >0.5 mg/L, complete eradication of planktonic cells was effected by all three antibiotics. The biofilm MICs for the three antibiotics were 3-7 twofold dilutions higher than the corresponding planktonic MICs (P<0.05). Vancomycin and linezolid exhibited similar median MICs against biofilms of neonatal isolates ranging from 16 to 32mg/L with comparable damage (44%-84% for vancomycin vs 56%-77% for linezolid). Their MICs against biofilms of isolates from adults were 128 mg/L and 4 mg/L, respectively (P<0.001). Vancomycin showed lower MIC than daptomycin against biofilms of neonatal isolates (16 mg/L vs 64 mg/L, respectively; P<0.05). Biofilm MIC of linezolid was lower than the corresponding daptomycin MIC for both age groups (neonatal isolates: 16 mg/L vs 64 mg/L; adult isolates: 4 mg/L vs 64 mg/L, P<0.05). Vancomycin and linezolid are equally effective against biofilms of neonatal blood isolates and both exhibit superior activity to daptomycin. In the adult group, linezolid is more efficacious than both vancomycin and daptomycin against biofilms, while vancomycin and daptomycin exhibit similar anti-biofilm activities. Our results suggest that vancomycin and linezolid show better anti-biofilm activity than daptomycin against biofilms of neonates and linezolid have increased activity against biofilms of adults.