An 8-week feeding trial was conducted to evaluate two vitamin C derivatives, L-ascorbyl-2-monophosphate-Mg (C2MP-Mg) and L-ascorbyl-2-monophosphate-Na (C2MP-Na), to satisfy the vitamin C requirement and to test their effects on the immune responses of juvenile grouper, Epinephelus malabaricus. C2MP-Mg and C2MP-Na were each supplemented at 20, 50, 80, 150, 250, and 400 mg kg )1 diet in the basal diet providing of 7, 18, 31, 51, 93, 145 mg ascorbic acid (AA) equivalent of C2MP-Mg kg )1 diet and 4, 10, 17, 31, 47, 77 mg ascorbic acid (AA) equivalent of C2MP-Na kg )1 diet, respectively. Basal diet without AA supplementation was included as control. Each diet was fed to triplicate groups of grouper (mean initial weight 3.20 ± 0.05 g). Fish fed diets supplemented with either C2MP-Mg or C2MP-Na had significantly (P < 0.05) greater weight gain (WG), feed efficiency and survival than those fed the unsupplemented control diet. Liver ascorbate concentrations in fish generally increased as dietary C2MP-Mg or C2MP-Na supplementation level increased. Haemolytic complement activity was higher in fish fed diets supplemented with 92 mg AA equivalent of C2MP-Mg kg )1 or 10-17 mg AA equivalent of C2MP-Na kg )1 than fish fed the unsupplemented control diet. Lysozyme activity was higher in fish fed ‡51 mg AA equivalent of C2MP-Mg kg )1 or ‡47 mg AA equivalent of C2MP-Na kg )1 than fish fed the unsupplemented control diet. Analysis by broken-line regression of WG indicated that the adequate dietary vitamin C concentration from each vitamin C derivative in growing grouper is 17.9 mg AA equivalent of 2MP-Mg kg )1 and 8.3 mg AA equivalent of C2MP-Na kg )1 , and it also indicated that C2MP-Mg is about 46% as effective as C2MP-Na in meeting the vitamin C requirement of grouper.
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Escherichia coli and Staphylococcus aureus are two food pathogens that cause severe food poisonings. Another problem found on a global level is the continuous increase of antimicrobial resistance in bacteria isolated from food. This study aimed to evaluate the antibacterial activity of Lactobacillus plantarum against pathogenic bacteria including E. coli and S. aureus and to study if L. plantarum with antibacterial activity contained the most plantaricin genes or not. A total of 50 lactic acid bacteria isolates (LAB) were evaluated for antibacterial activity and identified plantaricin genes by polymerase chain reaction (PCR) methods. Seven LAB isolates with antibacterial activity against S. aureus and E. coli were identified as Lactobacillus based on morphological physiological and biochemical properties. Using species-specific PCR and 16S rRNA gene sequencing, B0039 was identified as Lactobacillus paracasei, other isolates were identified as L. plantarum. 3 strains tested positive for all the genes in the plnABCD operon. The plnEFI operon was detected in four strains. Genes encoding for the two-peptide plnJ/K were detected only in 2 strains. Finally, the plnG/V was also found in 3 strains of L. plantarm. The plantarum gene sequences of B0055 were 97 to 100% similarity with the L. plantarum WCFS1. The findings suggest that LAB with bacteriocin genes can be used as an alternative mechanism to control drug resistant foodborne pathogens.
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