Inhibition of fructan-fermenting equine faecal bacteria and Streptococcus bovis by hops (Humulus lupulus L.) ß-acid.

AIMS: The goals of this study were to determine if ß-acid from hops (Humulus lupulus L.) could be used to control fructan fermentation by equine hindgut micro-organisms, and to verify the antimicrobial mode of action on Streptococcus bovis, which has been implicated in fructan fermentation, hindgut acidosis and pasture-associated laminitis (PAL) in the horse. METHODS AND RESULTS: Suspensions of uncultivated equine faecal micro-organisms produced fermentation acids when inulin (model fructan) was the substrate, but ß-acid (i.e. lupulone) concentrations ≥9 ppm inhibited lactate production and mitigated the decrease in pH. Inulin-fermenting Strep. bovis was isolated from the ß-acid-free suspensions after enrichment with inulin. The isolates were sensitive to ß-acid, which decreased the viable number of streptococci in faecal suspensions, as well as growth, lactate production and the intracellular potassium of Strep. bovis in pure culture. CONCLUSIONS: These results are consistent with the hypothesis that hops ß-acid prevented the growth of fructan-fermenting equine faecal bacteria, and that the mechanism of action was dissipation of the intracellular potassium of Strep. bovis. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacterial hindgut fermentation of grass fructans has been linked to PAL and other metabolic disorders in horses. Hops ß-acid is a potential phytochemical intervention to decrease the growth of bacteria responsible for PAL.

Arabidopsis ecotype variability in camalexin production and reaction to infection by Alternaria brassicicola.

Camalexin production was compared in 24 ecotypes of Arabidopsis thaliana. Detached Arabidopsis leaves were inoculated with Cochliobolus carbonum, an incompatible pathogen of Arabidopsis, to test the ability of each ecotype to produce camalexin. Whole plants were inoculated with Alternaria brassicicola, a crucifer pathogen, to determine if there was a correlation between the ability of an ecotype to produce camalexin and its resistance to A. brassicicola. All ecotypes were capable of producing camalexin, but the amounts produced relative to the Columbia ecotype (used as a standard) varied within and among ecotypes, and among experiments. Different degrees of resistance to A. brassicicola were observed among ecotypes, both macroscopically and microscopically. Extraction of A. brassicicola-inoculated leaves revealed that only four ecotypes (two resistant and two susceptible) produced easily detectable amounts of camalexin in response to this pathogen. TLC plate bioassays suggested that A. brassicicola was relatively insensitive to camalexin, thus casting some doubt on the importance of this compound in defense. These studies suggest that the role of camalexin in disease resistance varies among different Arabidopsis populations in nature, and they provide some clues to other possible determinants of resistance to A. brassicicola.

Photosensitization by 2-chloro-3,11-tridecadiene-5,7,9-triyn-1-ol: damage to erythrocyte membranes, Escherichia coli, and DNA.

The natural product 2-chloro-3,11-tridecadiene-5,7,9-triyn-1-ol (1) photosensitized the inactivation of Escherichia coli in the presence of near-ultraviolet light (320-400 nm; NUV) under both aerobic and anaerobic conditions. A series of E. coli strains differing in DNA repair capabilities and catalase proficiency exhibited indistinguishable inactivation kinetics following treatment with the chemical plus NUV. The presence of carotenoids did afford some protection to E. coli against inactivation under aerobic conditions, consistent with the involvement of singlet oxygen. The photosensitized hemolysis of human erythrocytes occurred more rapidly in the absence than in the presence of oxygen. Aerobically, the onset of hemolysis was partially inhibited by NaN3 and by 2,6-di-t-butyl-4-methylphenol (BHT) but not by superoxide dismutase (SOD). The aerobic lipid peroxidation observed in the membranes of erythrocyte ghosts was completely inhibited by BHT, and partially by NaN3, but not by SOD. These results suggest that either lipid peroxidation of the membrane is not the main cause of photohemolysis or that BHT has insufficient access to intact erythrocyte lipids to protect them. Aerobically, crosslinking of membrane proteins was also observed; it was not affected by SOD, but was partially inhibited by BHT and NaN3. The anaerobic photosensitized hemolysis of erythrocytes was more rapid; a radical mechanism was suggested since BHT inhibited the hemolysis to a greater extent than under aerobic conditions. Neither lipid peroxidation nor protein crosslinking was observed under conditions believed to be anaerobic. A light-dependent electron transfer to cytochrome c was obtained under argon but not under oxygen. Although induced mutations were not observed in the experiments with E. coli, 1 was capable of damaging both supercoiled pBR322 and Haemophilus influenzae transforming DNA in a manner that seemed to be equivalent under aerobic and anaerobic conditions. In conclusion, 1 can behave as typical photodynamic molecule under aerobic conditions but, in contrast to most photodynamic molecules, it is also phototoxic under anaerobic conditions. The extent to which the radical reactions detected under anaerobic reactions compete with the photodynamic processes when oxygen is present is not known.