Effects of antibiofilm compounds on the cellular and bacterial colonization of polimeric surfaces: a step towards biofunctionalization of implantable devices

Background

Periodontal and peri-implant diseases are infection pathologies related to the pathogenicity of the microorganisms involved [1]. The worldwide practice of indiscriminate and continuous use of antibiotics for the control and prophylaxis of bacterial pathogens has led to the development of bacterial resistance to most available antimicrobials [2]. Concurrently, the rapid increase in bacterial resistance to currently available antimicrobial drugs has led researchers to search for new sources of molecules active against bacterial pathogens, outlining a new generation of anti-infective drug development. A promising approach for the development of a new generation of antimicrobial drugs has arisen from the studies of host-pathogen interactions, which prompted a shift of drug targets from bacterial survival to pathogenicity control. Examples of potential non-conventional targets for microbial control are molecules and receptors involved in bacterial adherence to biotic and abiotic surfaces as well as signal systems controlling bacterial group behaviour of populations organised in biofilms, such as quorum sensing (QS) [3]. In contrast to conventional antibiotics, antimicrobial drugs directed against such unconventional targets do not jeopardise bacterial survival, imposing a low selection pressure and thus avoiding the development of resistance [4].

Methods

Here we analysed the effects of novel synthetic lactams, compounds derived from furanones which display recognized antibiofilm activity. Three synthetic lactams were tested against biofilm of Enterococcus faecalis grown over an implantable polymeric material (PLGA-HA). Inhibition assays of adhesion and biofilm formation, and SEM observation were used to quantify and qualify E. faecalis' biofilm formation. To assay for biofilm inhibition, bacterial strains were grown statically for 20 h at 37°C in TSB. Polystyrene 96-well microtitre plates were inoculated with 100 μL/well of bacterial suspension previously diluted to 5 × 10⁸ CFU/mL in TSB supplemented with 4% sucrose (w/v) and 3.5% (v/v) dimethyl sulphoxide (DMSO). Compounds to be tested for antibiofilm activity were prepared at a concentration of 175 μg/ml, in the same media as before, and added to the test wells. Biofilm inhibition capacity was assessed by CFU counting after bacterial disaggregation from the surfaces and microscopic analysis of the polymers. Cytotoxicity of the lactams against human fibroblasts and keratinocytes was tested, at four different concentrations (43,75; 87,5; 131,25 and 175 μg/ml), by MTT assay [5].

Results and conclusions

All compounds showed biofilm inhibition rates higher than 99%, as accessed by CFU counting and in agreement with images obtained by SEM. At the MIC (minimum inhibitory concentration) human cells viability indexes of all compounds were higher than those recommended for approval in clinical use. Results presented here indicate that lactams have excellent potential for use in the treatment of periodontal disease and in association with PLGA-HA can be used in the prevention of peri-implantitis disease.