Fish silage is a brown liquefied product achieved by the action of enzymes when finely grounded whole/parts of either single or mixed fish types are subjected to acidification. This study made a comparative assessment of biochemical and nutritive properties, especially the amino acid composition in supernatant phase of formic acid silages prepared from two fish types, Indian mackerel (Rastrelliger kanagurta) and false travely (Lactarius lactarius) representing fat fish (FF, fat content > 5%) and lean fish (LF, fat content < 5%), respectively during 35 days of fermentation (DoF). Significantly higher content of total amino acid (TAA) and free amino acids (FAA) were recorded in FFS (TAA, 41.2 ± 0.03 mg/g; FAA, 31.3 ± 0.003 mg/g) compared to LFS (TAA, 35.8 ± 0.07 mg/g; FAA, 18.26 ± 0.003 mg/g; FAA, 31.3 ± 0.003 mg/g) (p < 0.05). At the end of 35 DoF, the concentrations of amino acids such as asparagine, histidine, isoleucine, valine, cysteine, serine, lysine and arginine were significantly higher in FFS as compared to LFS. The relative amino acid composition of FFS and LFS varied in accordance with DoF and the relationship was found to be highly significant (ANOVA, p < 0.00001). High concentrations of l-amino acids such as leucine, glutamic acid and arginine were recorded in both FFS and LFS. In conclusion, the analysis suggested that a fermentation period of 25–30 days showed a significant effect on the composition of amino acids in both types of ensilage compared to other fermentation periods (p < 0.05). Considering the role of amino acids in enhancing the plant growth and proliferation, the findings of the present study are quite useful.
Isoxazolones are synthesised using easily available, economical and reusable silica (TLC grade) catalyst. High yields are obtained in aqueous reaction system with substrate tolerance without affecting the yield. This multigram scale, purification free method exhibits prospects for a large scale use in future. These compounds were screened for their potential application as quorum quenchers in pathogenic bacteria. The prepared compounds were analysed for quorum quenching (QQ) activity on Gram negative bioreporter strain Chromobacterium violaceum by inhibiting its pigment production i. e. violacein production in a concentration dependent manner. Some Isoxazolone derivatives showed very good quorum quenching activity. Moreover these derivatives also showed very good antibiofilm activity against both Gram negative (Pseudomonas aeruginosa ATCC 27853) and Gram positive (Staphylococcus aureus ATCC 6538) bacterial human pathogens through Quorum Quenching mechanism. Isoxazolones thus have enormous potential to be exploited in the medical field against bacterial infections caused by both Gram negative and Gram positive bacterial human pathogens.
Listeria monocytogenes, a foodborne pathogen and well known causative agent of listeriosis in humans that is also known to form biofilm on utensils used in the dairy industry is well studied for peptide-based Quorum sensing system (agr QS system). In the present study, we are reporting L. monocytogenes strain BN3 to respond to an acyl-homoserine lactone (AHL) by expression of virulence gene (hlyA) and the gene responsible for biofilm formation (srtA) using Real-Time PCR technology. It revealed that in L. monocytogenes, hlyA gene (encodes listeriolysin O) expression increased 0.7-fold in response to 500 nM AHL (C4-HSL treated) as compared to control. Also, in response to 500 nM AHL, (C4-HSL treated) strain BN3 showed 27-fold up-regulation of srtA gene (encodes enzyme sortase) as compared to control. Our study confirmed the cross-talk between Gram-positive and Gram-negative bacteria since L. monocytogenes strain BN3 responds to C4-HSL, which is normally produced by Gram-negative bacteria. Here, we suggest targeting both agr based QS and AHL based QS system together in L. monocytogenes to tackle biofilm formed on milk cans in dairy industries and when treating listeria infections.
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