Abstract
Animal manure application to soils is considered to be one of the main cause of antibiotic and bacterial pathogen spread in the environment. Pig livestock, which is the source of one of the most used fertilizer for cultivated land, is also a hotspot for antibiotics and antibiotic-resistant bacteria. Besides harsh chemical and physical sanitization treatments for the abatement of antibiotics and bacterial load in livestock waste, more sustainable and environmentally friendly strategies need to be considered. In this context, the use of natural substances which are proved useful for pest and disease control is currently under exploration for their role in the reduction of bacterial pathogen population. Among these, plants and derived products from the Brassicaceae family, characterized by the presence of a defensive glucosinolate-myrosinase enzymatic system, have been successfully exploited for years in agriculture using the so-called biofumigation technique against crop diseases. Although the application of biofumigation to suppress a range of soil borne pests has been well documented, no studies have been examined to reduce bacterial population in animal waste. In the present study, the release and the antibacterial activity of bioactive compounds deriving from different Brassicaceae defatted seed meals against pathogens and bacterial population in pig manure is addressed. Rapistrum rugosum and Brassica nigra defatted seed meals were found to be the most active products against tested pathogens and able to significantly reduce the bacterial load in the manure.
Highlights
Agricultural application of animal manure as a soil amendment and crop fertilizer is a common practice that has been used since ever
defatted seed meals (DSMs) containing GSLs belonging to the different classes according to the aglycone R-side chain chemical structure (Table 1) were chosen: sinigrin [allylGSL] (SIN), an aliphatic GSL, glucocheirolin [3-(methylsulfonyl)propyGSL] (GCH) and glucoerucin [4-(methylthio)butylGSL] (GER), two thiofunctionalized GSL with a different sulfur oxidation state, as well as two aromatic GSL, gluconasturtiin [2-phenylethylGSL] (GST), and glucotropaeolin [benzylGSL] (GTL)
The minimum inhibitory concentration (MIC) values were assessed by broth microdilution technique towards three human putative pathogens and the initial GSL concentration and the stoichiometry of the reaction were taken into account
Summary
Agricultural application of animal manure as a soil amendment and crop fertilizer is a common practice that has been used since ever. Sulforaphane, the ITC deriving from the glucoraphanin GSL, concentrated in broccoli and black kale seeds, showed its antimicrobial activity against Helicobacter pylori (Fahey et al 2013); benzyl isothiocyanate was found to be the most effective, among several ITCs tested, against Campylobacter jejuni, Escherichia coli, and Staphylococcus aureus, including some antibiotic-resistant phenotypes (Aires et al 2009; Dufour et al 2012; Nowicki et al 2016; Sofrata et al 2011); Moringa peregrine aqueous extracts were successful tested for the inhibitory activity against resistant strain of Salmonella enterica (Saleh et al 2017). The different GSL chemical structure determines the chemical and physical properties and biological activity of deriving hydrolysis products (ITCs), where the R-side chain is maintained (Dufour et al 2015; Leoni et al 1997). Erucin [4-(methylthio)butylITC], the ITC produced from GER, is a structural analogue of sulforaphane [(methylsulfinyl)butylITC] (SFN), the most frequently studied ITC for its preventive activity against a variety of cancers,
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