Bacterial adhesion forces with substratum surfaces and the susceptibility of biofilms to antibiotics

Abstract

Biofilms causing biomaterial-associated infection resist antibiotic treatment and usually necessitate the replacement of infected implants. Here we relate bacterial adhesion forces and the antibiotic susceptibility of biofilms on uncoated and polymer brush-coated silicone rubber. Nine strains of Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa adhered more weakly to brush-coated silicone rubber (-0.05 ± 0.03 to -0.51 ± 0.62 nN) than to uncoated silicone rubber (-1.05 ± 0.46 to -5.1 ± 1.3 nN). Biofilms of weakly adhering organisms on polymer brush coatings remained in a planktonic state, susceptible to gentamicin, unlike biofilms formed on uncoated silicone rubber.

Fig 1

Forces of bacterial adhesion (F_adh) to uncoated and polymer brush-coated silicone rubber, showing significant reductions in adhesion forces (P < 0.05) for all nine strains after the silicone rubber surface was coated with a polymer brush.

Fig 2

CLSM overlay images and optical sections of 20-h-old intact biofilms grown in the absence (−) or presence (+) of 50 μg/ml gentamicin on uncoated silicone rubber or polymer brush-coated silicone rubber. Live and dead bacteria show green and red fluorescence, respectively, while EPS yields blue fluorescent patches. Bars, 75 μm. Panels: a, S. aureus ATCC 12600; b, S. epidermidis 138; c, P. aeruginosa #3.

Fig 3

Surface coverage as a function of time on uncoated silicone rubber and polymer brush-coated silicone rubber by biofilms grown in the absence or presence of various concentrations of gentamicin (open squares, no antibiotic; open triangles, 0.5 μg/ml gentamicin; gray triangles, 5 μg/ml gentamicin; black triangles, 50 μg/ml gentamicin) and coverage by live organisms after 20 h of growth (green bars). Gentamicin was introduced after 4 h of growth. Error bars represent standard deviations of two separate experiments. Panels: a, S. aureus ATCC 12600; b, S. epidermidis 138; c, P. aeruginosa #3. An asterisk indicates a significant difference (P < 0.05) between uncoated silicone rubber and polymer brush-coated silicone rubber in surface coverage by biofilm after 20 h of growth. The symbol # indicates a significant difference (P < 0.05) between the numbers of live bacteria in 20-h-old biofilms on silicone rubber and polymer brush-coated silicone rubber.