Anti- staphylococcal biofilm efficacy of Daptomycin and Tigecycline: an in vitro evaluation

Given the potential for antibiotic resistance featuring biofilm–based infections, one on the most fascinating challenge is currently to develop new treatment strategies specifically designed for sessile growing bacteria. In fact, a highly competitive race is under way from a decade among drug companies to develop terapeutic strategies based on new antimicrobials able to counteract biofilm–based infections, especially those caused by the most insidious bugs . The aim of our study was to evaluate the in vitro anti-biofilm activity of Daptomycin and Tigecycline since these two antibiotics claim a strong efficacy against biofilm-based staphylococcal infections. In all the experiments the strong biofilm-producer Staphylococcus epidermidis ATCC 35984 strain was used. Antibiotic susceptibility of planktonic bacteria was determined by the disk diffusion test and the Minimum Biofilm Eradication Concentration (MBEC) was assessed by the 96-wells microplate assay. On the basis of the MBEC results, biofilm eradication assays were prepared on 96-well plates and evaluated by crystal violet staining and colony forming units assay. Untreated and antibiotic-treated biofilms were examined by a Field Emission Scanning Electron Microscope (Zeiss Sigma) to analize their surface features , while a Live/Dead Baclight bacterial viability kit was adopted for confocal laser scanning microscopy (CLSM) observations. In our experiments a significant ability in reducing a mature biofilm of S. epidermidis was exhibited at similar levels by Daptomycin and Tigecycline . However, both these drugs failed to show the complete biofilm disruption and a full bactericidal effect despite the antibiotic concentrations used would be 100 times higher than MIC.