Evaluation of Anti biofilm and Antibiotic Synergistic Activities of Silver Nano particles Against Some Common Bacterial Pathogens

Nowadays silver nanoparticles (AgNPs) are used as antimicrobial due to its well known physical, chemical, and biological properties. The current study was planned to search the antibacterial and anti biofilm activities of silver nanoparticles alone and in combination with conventional antibiotics against some field isolates of common bacterial pathogens.
Standard strains of Escherichia coli, Salmonella enteritidis, Staphylococcus aureus and Streptococcus agalactiae, in addition to nine field isolates for each strain (totally 40 strains, 10 for each) were used. Macro dilution method for determination of MIC of AgNPs and antibiotics against isolates was used. Biofilm formation was evaluated by micro titer plates. Disc diffusion method was used for assaying bactericidal activities of antibiotics and their combinations with AgNPs against the isolates.
Mean MICs of AgNPs for Salmonella serotypes, E. coli, S. aureus and S. agalactiae were 3.125, 6.25, 6.25 and 12.5 ug/mL respectively. S. aureus and S. agalactiae showed more sensitivity (increase in fold) to examined antibiotics plus AgNPs compared to Salmonella serotypes and E. coli. The results showed that AgNPs have strong anti bactericidal and anti biofilm activity against the examined pathogens. Synergistic and antagonistic effects of AgNPs in combination with tetracyclin, gentamicin, streptomycin, kanamycine, cephalosporin and penicillin were observed in different cases.
AgNPs alone or in combination with antibiotics could potentially be used as an effective antibacterial and anti biofilm agent. However, our results show that synergistic interactions of combined antibiotics and AgNPs cannot be considered as a rule.