Abstract

Antimicrobial effect of silver nanoparticles on two fish pathogens, Lactococcus garvieaeand Streptococcus iniae was investigated by microdilution method. A total of 16 isolates ofL. garvieae and S. iniae that were obtained from diseased rainbow trout during 2009 to 2011 were examined. Antimicrobial effects of the compound were evaluated according to the broth microdilution method by determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). According to the results MIC ranged from 1.12 to 5 µgml^-1 for L. garvieae and 1.12 to 2.5 µgml^-1 for S. iniae isolates. The mean MIC value was 2.59 and 2.1 for L. garvieae and S. iniae, respectively. The MBC was also calculated for the examined isolates as MBC ranged from 2.5 to 10 µgml^-1 with the mean of 5.27 and 3.57 for L. garvieae and S. iniae, respectively. The results showed that S. iniaestrains were more sensitive to silver nanoparticles than L. garvieae strains. This study demonstrated the in vitro antimicrobial effects of silver nanoparticles on the examined bacteria although the efficacy of silver nanoparticles in fish ponds in different conditions needs more investigations.

Key words: Silver nanoparticles, Lactococcus garvieae, Streptococcus iniae.