ABSTRACT
Increasing developments in nanotechnology in recent years have raised the possible risk of release of nanoparticles into the aquatic environment, which could adversely affect organisms. Silver nanoparticles possess antibacterial activities and constitute almost 567o of total manufactured nanoparticles which are currently in use. The aim of this study was to evaluate the effects of colloidal silver nanoparticles on bacterial flora of rainbow trout gut. The Induced Coupled Plasma [ICP], Zetasizer and Transmission Electron Microscope [TEM] methods were used in order to ensure the quality of silver nanoparticles. 90 Fish [25 +/- 0.5 g] in Faculty of Marine Sciences were exposed to zero and 1 mg/L of silver nanoparticles over 14 days. Total viable bacterial counts and psycrotrophic bacteria, entrobacteriaceae and lactic acid bacteria counts of fish's gut and total viable bacterial counts and psycrotrophic bacteria counts of water were determined. There was not any effect of nonoparticles on the bacterial counts [lactic acid bacteria, psycrotrophic and enterobacteriaceae] of the fish's gut and bacterial counts [psycrotrophic and total viable of the water. However, there were significant differences between control and 1 ppm treatments based on the size and color of psycrotrophic colonies. Furthermore, the psycrotrophic bacterial counts of fish's gut in the 1 ppm treatment showed significant increase [6.49 +/- 0.02 1og cfu/g] compared to the control group [5.72 +/- 0.17 log cfu/g] [p<0.05]. The psycrotrophic bacteria represented the most sensitivity to nanoparticles among all studied bacterial groups [p<0.05]; so, changes in the number of these bacteria may be considered as an indicator in monitoring the release and presence of silver nanoparticles in aquatic ecosystems.
Subject(s)
Animals , Nanoparticles , Silver , EcosystemABSTRACT
Food poisoning caused by Listeriamonocytogenes results in death in 30% of the cases. Considering the high probability of L. monocytogenes contamination of local fish, the present study aimed at investigating the effects of thyme [Zataria multiflora Boiss] essential oil [EO] and nisin, individually and in combination, on the growth of L. monocytogenes in minced silver carp during refrigerated storage. Minced fish samples were inoculated with 1x10[4] cfu/g of L. monocytogenes. A total of 11 samples were inoculaetd with thyme EO at a concentration [weight/volume]of 0.3%, 0.8% or 1.2%, nisin at a concentration of 500 or 1000 IU/g, or a combination of the two. The treated and control samples were packaged in plastic bags and kept at refrigerator temperature for 12 days.. Samples were cultured on CHROMagarTM Listeria every 2 days and the bacteri counted. Nisin at two different levels [500 and 1000 IU/g]could not inhibit the growth of L.monocytogenes to a level below the acceptable level in raw food [100 cells/g]. The antibacterial activity of nisin decreased during the storage period, while simultaneous use of nisin and thyme EO at a concentartion of 0.8 and 1.2% reduced L. monocytogenes viable count to a level below the acceptable limit during 12 days. A combination of 0.8% thyme [weight/volume]and 1000 IU/g nisin has the best inhibitory effect on growth of L. monocytogenes in minced silver carp during cold [4[degree sign] C] storage