Antibacterial effects of glucosinolate-derived hydrolysis products against enterobacteriaceae and enterococci isolated from pig ileum segments.

The aim of this study was to evaluate the effects of various glucosinolate-derived hydrolysis products (HP) as antibacterial compounds against Enterobacteriaceae and Enterococcaceae isolated from intestinal segments of healthy pigs collected directly from slaughter-houses in the North of Portugal. Using a previously described disk-diffusion bioassay, all HP were tested at six different doses (0.015, 0.15, 0.75, 1.5, 3.0, and 15.0 µmoles) in dimethyl-sulfoxide (DMSO), with the exception of sulforaphane (SFN), which was not tested at 15.0 µmoles. Positive (antibiotic standard) and negative controls (DMSO) were included in all experiments. All the experiments were conducted in triplicate. In vitro inhibition of the bacterial growth by the HP was proportional to the concentration used and in many cases was even higher than for the gentamycin, the antibiotic control. The results clearly showed that the glucosinolates-derived HPs were very effective in vitro inhibitors of bacterial growth. The natural products, and specifically the isothiocyanates, should be evaluated as potential alternative control agents for potentially pathogenic bacteria (e.g., dietary amendment of pig foods with glucosinolate-containing plants).

Antimicrobial susceptibility of Aeromonas spp. isolated from pig ileum segments to natural isothiocyanates.

With this study we intend to evaluate the effects of 8 different glucosinolate hydrolysis products including isothiocyanates as antibacterial compounds against Aeromonadaceae, isolated from intestinal segments of pigs collected directly from slaughter-houses in the North of Portugal. Four Aeromonas species, A. allosaccharophila, A. hydrophila, A. media and A. veronii were identified. Using disc-diffusion bioassay all compounds were tested at 6 different doses (0.015, 0.15, 0.75, 1.5 and 3.0 µmoles) in dimethyl-sulfoxide (DMSO). Antibiotic standard (gentamicin) and DMSO (negative control) were included in all experiments. Minimum and maximum dose inhibitions (in µmoles) were assessed. To our knowledge, this is the first study of antimicrobial activity of glucosinolate hydrolysis products against Aeromonas species. The results showed that glucosinolate hydrolysis products and particularly the isothiocyanates have antimicrobial activity, which was proportional to the concentration used. However, not all revealed the same tendency, which means that the chemical structure of each compound is fundamental to understand their effectiveness. Among the different isothiocyanates the benzylisothiocyanate, sulforaphane and 2-phenylethylisothiocyanate were the most effective in vitro inhibitors of bacterial growth. This in vitro study provides enough data to demonstrate the potential use of these natural dietary chemicals for treating infectious diseases caused by Aeromonas spp.