Studies on the effect of Lactococcus garvieae of dairy origin on both cheese and Nile tilapia (O. niloticus)

The aims of this study were to evaluate the activity of Lactococcus garvieae of dairy origin against pathogenic bacteria during cheese manufacture and its suitability and safety as a probiotic on Nile tilapia (Oreochromis niloticus). For these purposes, Lactococcus garvieae isolated from raw cow milk was tested to control the growth of Staphylococcus aureus in artificially contaminated cheese during storage under refrigeration. Also a feeding experiment was conducted on 120 Oreochromis niloticus using a diet containing Lactococcus garvieae as a probiotic bacteria against pathogenic S. aureus. The findings of this study showed that Lactococcus garvieae of dairy origin produced inhibitory substances against pathogenic microorganisms. The selected strain had a good inhibitory activity against Staphylococcus aureus in artificially contaminated cheese during refrigerated storage. Concerning fish experiment, it showed no evidence of disease in fish that were fed a diet containing Lactococcus garvieae, and showed a higher survival rate than others. Further investigations for purification of the produced inhibitory substance and confirming that is a bacteriocin-like substance are needed. Nonetheless, it is the first report of using L. garvieae of dairy origin as a probiotic for controlling the pathogenic Staphylococcus aureus in Oreochromis niloticus.