Comparison of rumen microbial inhibition resulting from various essential oils isolated from relatively unpalatable plant species

Antibiotic-resistant bacteria in the guts of insects feeding on plants: prospects for discovering plant-derived antibiotics

BACKGROUND

Although plants produce many secondary metabolites, currently none of these are commercial antibiotics. Insects feeding on specific plants can harbour bacterial strains resistant to known antibiotics suggesting that compounds in the plant have stimulated resistance development. We sought to determine whether the occurrence of antibiotic-resistant bacteria in insect guts was a widespread phenomenon, and whether this could be used as a part of a strategy to identify antibacterial compounds from plants.

RESULTS

Six insect/plant pairs were selected and the insect gut bacteria were identified and assessed for antibiotic susceptibilities compared with type strains from culture collections. We found that the gut strains could be more or less susceptible to antibiotics than the type strains, or show no differences. Evidence of antibacterial activity was found in the plant extracts from five of the six plants, and, in one case Catharanthus roseus (Madagascar Periwinkle), compounds with antibacterial activity were identified.

CONCLUSION

Bacterial strains isolated from insect guts show a range of susceptibilities to antibiotics suggesting a complex interplay between species in the insect gut microbiome. Extracts from selected plants can show antibacterial activity but it is not easy to isolate and identify the active components. We found that vindoline, present in Madagascar Periwinkle extracts, possessed moderate antibacterial activity. We suggest that plant-derived antibiotics are a realistic possibility given the advances in genomic and metabolomic methodologies.

Digestion and absorption ofEucalyptus essential oils in greater glider (Petauroide svolans) and brushtail possum (Trichosurus vulpecula)

Measurements were made of the quantity and composition of the steam-volatile essential oils in gastrointestinal tract contents of greater gliders fedEucalyptus radiata foliage and brushtail possums fedE. melliodora foliage. In both species, there was less oil in the stomach contents than in an equivalent mass of foliage. Only minor losses of leaf oils occurred during mastication by greater gliders, and absorption from the stomach appeared to be the major reason for the difference in the oil content of ingested leaves and of stomach contents. The apparent digestibility of oils over the whole gut was 96-97 %, although oils from the cecum and feces of both species contained compounds not present in the original leaf oils. Absorption of oils before they reach the hindgut should reduce the severity of antimicrobial effects but may involve a metabolic cost to the animal in detoxification and excretion.

Ethanolic Extracts of California Mugwort (Artemisia douglasiana Besser) Are Cytotoxic against Normal and Cancerous Human Cells

California mugwort (Artemisia douglasiana Besser) is used by many tribes throughout California to treat a variety of conditions, including colds, allergies, and pain. California mugwort is also utilized as women's medicine. Its use is on the rise outside of Native communities, often without the guidance of a traditional healer or experienced herbalist. Because it has been shown to have antiproliferative activity against plant and animal cells, we investigated whether California mugwort extracts have an effect on normal human cells as well as estrogen receptor positive (ER⁺) and estrogen receptor negative (ER^-) human breast cancer cells. Ethanolic and aqueous extracts of A. douglasiana leaves were tested for cytotoxicity against unstimulated normal human peripheral blood mononuclear cells (hPBMC), as well as against an ER⁺ human breast cancer cell line (BT-474) and an ER^- human breast cancer cell line (MDA-MB-231). An ethanolic leaf extract killed hPBMC, BT-474, and MDA-MB-231 cells with IC₅₀ values of 23.6 ± 0.3, 27 ± 5, and 37 ± 4 μg/ml, respectively. An aqueous extract killed hPBMC with an IC₅₀ value of 60 ± 10 μg/ml, but had no effect on the two cancer cell lines at concentrations up to 100 μg/ml. The results of this study indicate that the cytotoxicity of California mugwort extends to normal human cells, as well as cancerous cells. Therefore, until further is known about the safety of this medicine, caution should be taken when consuming extracts of California mugwort, whether as a tincture or as a tea.

Effects of essential oils on rumen fermentation, milk production, and feeding behavior in lactating dairy cows

Seven ruminally cannulated lactating Holstein dairy cows were used in an incomplete Latin rectangle design to assess the effects of 2 commercial essential oil (EO) products on rumen fermentation, milk production, and feeding behavior. Cows were fed a total mixed ration with a 42:58 forage:concentrate ratio (DM basis). Treatments included addition of 0.5 g/d of CE Lo (85 mg of cinnamaldehyde and 140 mg of eugenol), 10 g/d of CE Hi (1,700 mg of cinnamaldehyde and 2,800 mg of eugenol), 0.25 g/d of CAP (50mg of capsicum), or no oil (CON). Cows were fed ad libitum twice daily for 21 d per period. Dry matter intake, number of meals/d, h eating/d, mean meal length, rumination events/d, h ruminating/d, and mean rumination length were not affected by EO. However, length of the first meal after feeding decreased with addition of CE Hi (47.2 min) and CAP (49.4 min) compared with CON (65.4 min). Total volatile fatty acids, individual volatile fatty acids, acetate:propionate ratio, and ammonia concentration were not affected by EO. Mean rumen pH as well as bouts, total h, mean bout length, total area, and mean bout area under pH 5.6 did not differ among treatments. Total tract digestibility of organic matter, dry matter, neutral detergent fiber, acid detergent fiber, crude protein, and starch were not affected by EO. Milk yield and composition did not change with EO. In situ dry matter disappearance of ground soybean hulls was not affected by EO. However, organic matter disappearance of soybean hulls with CE Hi tended to decrease compared with CON. Compared with CON, neutral detergent fiber disappearance (41.5 vs. 37.6%) and acid detergent fiber disappearance (44.5 vs. 38.8%) decreased with addition of CE Hi. The CE Lo had no effect on rumen fermentation, milk production, or feeding behavior but CAP shortened the length of the first meal without changing rumen fermentation or production, making it a possible additive for altering feeding behavior. The CE Hi negatively affected rumen fermentation and shortened the length of the first meal, suggesting that a dose of 10 g/d is not beneficial to lactating dairy cows.

Decrease of ruminal methane production in Rusitec fermenters through the addition of plant material from rhubarb (Rheum spp.) and alder buckthorn (Frangula alnus)

Roots of rhubarb (Rheum spp.) and bark of alder buckthorn (Frangula alnus) were tested as feed additives for decreasing ruminal methane production released from anaerobic fermentation of a forage-based diet in a rumen-simulating fermenter (Rusitec). Sixteen fermentation units (vessels) were set up for the experiment lasting 19 d. Treated vessels were supplied with 1g/d of rhubarb or alder buckthorn (4 vessels per plant species); another 4 vessels received 12 microM sodium monensin (positive control), and the remaining 4 vessels were controls (no additive). Upon termination of the experimental period, batch cultures were inoculated with the liquid contents of the vessels for examining in vitro fermentation kinetics of cellulose, starch, barley straw, and the same substrate used in the Rusitec cultures. Monensin induced changes in fermentation in agreement with those reported in the literature, and inocula from those cultures decreased the fermentation rate and total gas produced in the gas kinetics study. Rhubarb decreased methane production, associated with limited changes in the profile of volatile fatty acids throughout the duration of the study, whereas digestibility and total volatile fatty acids production were not affected. Rhubarb inocula did not affect gas production kinetics except for cellulose. Alder buckthorn decreased only methane concentration in fermentation gas, and this effect was not always significant. The use of rhubarb (milled rhizomes of Rheum spp.) in the diets of ruminants may effectively modulate ruminal fermentation by abating methane production, thus potentially involving productive and environmental benefits.

Monoterpene effect on feeding choice by deer

A previous study showed that Sitka black-tailed deer (Odocoileus hemionus sitkensis) consumption was negatively correlated with monoterpene content in western redcedar (Thuja plicata). To test whether these monoterpenes were deterrent to Sitka black-tailed deer, we performed feeding choice experiments with four hydrocarbon (sabinene, myrcene, alpha-pinene, and d + l-limonene) and one oxygenated (alpha,beta-thujone) monoterpene solution at their highest natural concentration in western redcedar foliage. To test whether deer response was species specific, we ran similar experiments on European roe deer (Capreolus capreolus) and rusa deer (Cervus timorensis russa). In all experiments, monoterpenes were repellent. Solutions with alpha,beta-thujone, the major monoterpene in redcedar leaves, were the most repellent of the solutions tested. We then analyzed how black-tailed and roe deer responded to (1) an increase in concentration of the monoterpenes with the weakest repellent effects (hydrocarbon monoterpenes) and (2) a decrease in concentration of the monoterpene with strongest effect (alpha,beta-thujone). Repellency tended to increase with concentration for hydrocarbon monoterpenes, but remained strong for alpha,beta-thujone. As wild deer regularly feed on plants containing monoterpenes, this raises the question as to how the animals deal with these molecules.

Food selection by the South Indian leaf-monkey, Presbytis johnii, in relation to leaf chemistry

The leaf-monkey Presbytis johnii has been found to exhibit considerable selectivity in its dietary utilization of mature foliage in a rain-forest habitat. To investigate the basis of this selectivity and to examine the hypothesis that the observed selection is related to the digestibility and toxicity of the available foliage, chemical analyses have been made on 16 of the most important tree species in the monkey's habitat. It has been found that the most heavily used items, which form a staple part of the diet of P. johnii, are characterized by a low fibre content and a very low condensed tannin content. However, neither class of compound is an absolute feeding deterrent as minor, but still significant, mature leaf food items contain considerable amounts of both. It is suggested that the feeding deterrents in these minor items, which may be ingested to supply specific dietary requirements, can perhaps be tolerated because of their dilution in the gut by the dietary staples. An examination of the pepsin/cellulase digestibility of available mature foliage showed that the staple food items tended to be highly digestible. Little correlation has been found between alkaloid content and food selection and it is suggested that the colobine forestomach microflora has the ability to detoxify at least some alkaloids. Additional data on mature leaf petioles and young leaves suggest that the high ratio of cell-sap to cell-wall in these items, and their related high digestibility, explain the high relative abundance of these items in the P. johnii diet.

Forest fires and the snowshoe hare-Canada lynx cycle

This paper shows that there is a reasonable coincidence between the Canada lynx cycle and the occurrence of forest and brush fires. Fires set in motion plant succession, potentially leading to an increase in snowshoe hares (Grange, 1965). Snowfall is also correlated with the lynx cycle and tends to account for the variation not accounted for by fires. I conclude that Grange's (1949, 1965) hypothesis that fire and plant succession drive the snowshoe hare cycle deserves serious consideration, as do Butler's (1962) and Watt's (1968, 1973) suggestions that precipitation may drive or decisively modify furbearer 'cycles'. On this evidence, the snowshoe hare-Canada lynx cycle seems likely to be a forced oscillation rather than a predator-prey, parasitehost, or herbivore-vegetation limit cycle, as proposed by several authors. Fire clearly appear to be a periodic phenomenon, not-withstanding the difficulty of showing periodicity in simple weather time series. Fire is itself a meteorological phenomenon, although complexly related to simple weather variables.