Study effect of ascorbic acid on Streptococcus iniae and Lactococcus garvieae isolated from reared Oncorhynchus mykiss in invitro condition

Developing safe methods to maintain quality of harvested fish during storage and inhibiting growth of pathogens is crucial. On the other hand, using chemical preservatives to control the pathogens is a great health concern for us. Therefore, it is desirable to use natural preservatives with antibacterial properties for keeping health the harvested aquatic products. This study was conducted to evaluate effect of separate and synchronized activities of acid ascorbic so their improving anti-bacterial effect by pH alternations on Streptococcus iniae and Lactococcus garviae isolated from reared rainbow trout of province. We assessed the antibacterial effects of different concentrations of ascorbic acid (0, 19.53, 39.06, 78.13, 156.25, 312.5, 625, 1250, 2500, 5000 µg/mL), separately and simultaneously, in vitro on growing Streptococcus iniae and Lactococcus garviae under different pH 5.5, 6 and 7 by microdilution and spectrophotometrically methods. In microdilution assessment method, the most effect of growth inhibitory on the both of bacteria by ascorbic acid was observed in concentration 2500 µg/L under pH 5.5 and 6; nevertheless less inhibitory was observed in pH 7 by more concentration of the ascorbic acid, as MIC 5000 µg/mL. Considering the mentioned results, decreasing pH from 7 to 6 and 5.5 could increase inhibitory effect of ascorbic acid on both growing Streptococcus iniae and Lactococcus garviae activities.