Abstract
Aim
The primary aim of this in vitro study was to test the efficacy of daptomycin to eradicate staphylococcal biofilms on various orthopedic implant surfaces and materials. The secondary aim was to quantitatively estimate the formation of staphylococcal biofilm on various implant materials with different surface properties.
Method
We tested six clinically important biomaterials: cobalt chrome alloy, pure titanium, grid-blasted titanium, porous plasma-coated titanium with/without hydroxyapatite, and polyethylene. Two laboratory strains of bacteria commonly causing PJI were used, namely Staphylococcus aureus* and Staphylococcus epidermidis*. After overnight incubation with biofilm formation, the test samples were washed and individually exposed to increasing daptomycin concentrations (4–256 mg/l) during 24-hours. Samples were subsequently sonicated in order to detect dislodged biofilm bacteria on blood agar plates by viable growth and transferred to a microcalorimeter*** for real-time measurement of growth related heat flow during 24-h incubation. Minimal biofilm eradication concentration (MBEC) was determined as the lowest concentration of antibiotic required to eradicate the biofilm bacteria on the sample.
The time to detection expressed as the heat flow >50 µW (TTD-50) indirectly quantifies the initial amount of biofilm bacteria, with a shorter TTD-50 representing a larger amount of bacteria.
Results
MBEC of S. aureus biofilm on smooth metallic surfaces (median 6 mg/l, range 4–8 mg/l) was significantly lower than the rough/porous metallic surfaces (median 128 mg/l, range 32–256 mg/l; p<0.001). Variations of MBEC in experiments with S. epidermidis biofilms on test samples with smooth or rough/porous surface was found non-significant (p=0.25).
Mean TTD-50 (±SD) of S. aureus biofilms on rough/porous metallic samples (2.3 ±1.1 hours) was significantly lower than smooth metallic samples (6.7 ±0.4 hours, p<0.001) and polyethylene (5.3 ±0.5 hours, p<0.001). Mean TTD-50 with S. epidermidis biofilm on smooth metals (3.9 ± 1.0 hours) was also significantly higher than their rough/porous counterparts (2.0 ± 1.0 hours, p=0.010).
Conclusions
Growth of biofilm bacteria on orthopedic materials are variably influenced by exposure to the potent antimicrobial effect of high-dose daptomycin. In this study, the main factor decisively influencing biofilm quantity and daptomycin susceptibility of staphylococcal biofilms was the irregular surface topography.
* ATCC® 29213™
** ATCC® 35984™
*** TAM III
