Antimicrobial activity of Se0/Te0–based nanoparticles of bacterial origin

In the last few decades, the emergence of bacterial resistance to antibiotics has become a common phenomenon in both community and hospital setting. As a consequence, the effectiveness of antibiotic treatment of bacteriabased infection has progressively decreased. In particular, the treatment of biofilm-associated infection is problematic, since bacteria grown in biofilm mode are more tolerant to conventional antibiotics and biocides compared to free swimming cells. Therefore, it’s necessary to develop and test new antimicrobial compounds having both bactericidal potential and biofilm eradication activity against multidrug-resistant bacteria. In recent years, the employment of metallic nanoparticles has emerged as an alternative to the use of organic compounds as antimicrobial agents. Several studies has been focused particularly on the antimicrobial activity of silver nanoparticles: however other metal or metalloid nanoparticles have exhibited a promising bactericidal capability. However, one of the major drawback for the employment of nanoparticles is the cost associated with the traditional physical-chemical methods of synthesis and the production of toxic substances as byproduct. For these reasons, there is a considerable amount of interest in developing new and eco-friendly processes for the manufacturing of nanoparticles. In the present work, Se0 and Te0-based nanoparticles were bio-synthesized employing the selenite and telluritereducing capability of two bacterial strains isolated from polluted environments: Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. E. By regulating culture conditions and exposition time, we were able to produce nanoparticles of different dimensions, between 50 and 200nm. The nanoparticles were tested against planktonic and biofilms cultures of three common pathogenic strains: Escherichia coli JM109, Pseudomonas aeruginosa PAO1 and Staphylococcus aureus ATCC 25923. We evaluated both the inhibition activity against biofilm and planktonic growth and the eradication activity against biofilms established for 24 hours. To measure these parameters we determined both the minimum biocidal concentration (MBC) and the minimum biofilm eradication concentration (MBEC). In addition, we observed the effect of increasing concentrations of nanoparticles on biofilm structure using Confocal Laser Scanning Microscopy (CLSM). Our results indicate that both Se0 and Te0 nanoparticles possess antimicrobial and biofilm eradication activity. In particular Se0 nanoparticles exhibited antimicrobial activity at lower concentration. Preliminary data suggests that the activity seemed to be dependent on the dimension of the nanoparticles: indeed, the highest activity was shown by the nanoparticles smaller in size. The key observation is that bacteria growth in biofilm mode didn’t exhibit a higher level of resistance against the nanoparticles antimicrobial action. Results described in this study suggest a possible application of both Se0 and Te0 nanoparticles as an effective antimicrobial agent with a high biofilm eradication capacity.