The use of and search for drugs and dietary supplements derived from plants have accelerated in recent years. Ethnopharmacologists, botanists, microbiologists, and natural-products chemists are combing the Earth for phytochemicals and “leads” which could be developed for treatment of infectious diseases. While 25 to 50% of current pharmaceuticals are derived from plants, none are used as antimicrobials. Traditional healers have long used plants to prevent or cure infectious conditions; Western medicine is trying to duplicate their successes. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found in vitro to have antimicrobial properties. This review attempts to summarize the current status of botanical screening efforts, as well as in vivo studies of their effectiveness and toxicity. The structure and antimicrobial properties of phytochemicals are also addressed. Since many of these compounds are currently available as unregulated botanical preparations and their use by the public is increasing rapidly, clinicians need to consider the consequences of patients self-medicating with these preparations.

Plant Products as Antimicrobial Agents

The process of surface adhesion and biofilm development is a survival strategy employed by virtually all bacteria and refined over millions of years. This process is designed to anchor microorganisms in a nutritionally advantageous environment and to permit their escape to greener pastures when essential growth factors have been exhausted. Bacterial attachment to a surface can be divided into several distinct phases, including primary and reversible adhesion, secondary and irreversible adhesion, and biofilm formation. Each of these phases is ultimately controlled by the expression of one or more gene products. Ultrastructurally, the mature bacterial biofilm resembles an underwater coral reef containing pyramidal or mushroom-shaped microcolonies of organisms embedded within an extracellular glycocalyx, with channels and cavities to allow the exchange of nutrients and waste. The biofilm protects its inhabitants from predators, dehydration, biocides, and other environmental extremes while regulating population growth and diversity through primitive cell signals. From a physiological standpoint, surface-bound bacteria behave quite differently from their planktonic counterparts. Recognizing that bacteria naturally occur as surface-bound and often polymicrobic communities, the practice of performing antimicrobial susceptibility tests using pure cultures and in a planktonic growth mode should be questioned. That this model does not reflect conditions found in nature might help explain the difficulties encountered in the management and treatment of biomedical implant infections.

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Bacterial Adhesion: Seen Any Good Biofilms Lately?

The effect of condensed tannins on the nutrition and health of ruminants fed fresh temperate forages: a review

Analysis of condensed tannins: a review

Proanthocyanidins (PA) (condensed tannins) and hydrolyzable tannins (HT) are the two major classes of tannins. Proanthocyanidins are flavonoid polymers. Hydrolyzable tannins are polymers of gallic or ellagic acid esterified to a core molecule, commonly glucose or a polyphenol such as catechin. Proanthocyanidins are the most common type of tannin found in forage legumes. Problems in the analysis of tannins are that sample processing and drying decrease extraction and reactivity, suitable standards are unavailable, and quantitative analytical methods are poorly correlated with enzyme inhibition, protein precipitation, and nutritional effects. Hydrolyzable tannins are potentially toxic to ruminants. Pyrogallol, a hepatotoxin and nephrotoxin, is a product of HT degradation by ruminal microbes. Proanthocyanidins are considered to be non-toxic because they are not absorbed, but they are associated with lesions of the gut mucosa. Research on tannins in forage legumes has determined their effects on protein digestion and metabolism but more research on tannin structure in relation to digestion of specific proteins is needed. The widely accepted explanation for positive effects of PA on protein digestion and metabolism is that PA-protein complexes escape ruminal degradation and the protein is available in the lower tract. This proposed mechanism may be incorrect because PA also complex carbohydrates, endogenous proteins, and microbial products and the degradability of PA-protein complexes by ruminal microbes has not been adequately studied. Several alternative hypotheses (to escape protein) that explain the effect of PA on protein digestion and metabolism in ruminants are also consistent with experimental results on forage legumes. These include increased microbial protein synthesis, increased use of endogenous nitrogen in the rumen, and increased secretion of salivary glycoproteins. Research on manipulating the content and type of PA in forage legumes is justified because they are associated with non-bloating legumes, lower soluble non-protein nitrogen in silage, and improved efficiency of protein utilization. Research on the biosynthesis, molecular genetics, and cell biology of PA in forage legumes needs to be integrated with research on toxicology and nutrition.

Nutritional toxicology of tannins and related polyphenols in forage legumes

Sainfoin leaf condensed tannins inhibited growth and protease activity in Butyrivibrio fibrisolvens A38 and Streptococcus bovis 45S1 but had little effect on Prevotella ruminicola B(1)4 or Ruminobacter amylophilus WP225 Tannins bound to cell coat polymers in all strains Morphological changes in B fibrisolvens and S bovis implicated the cell wall as a target of tannin toxicity

Effects of Sainfoin (Onobrychis viciifolia Scop.) Condensed Tannins on Growth and Proteolysis by Four Strains of Ruminal Bacteria

The effect of condensed tannins from birdsfoot trefoil (Lotus corniculatus L.) on the cellulolytic rumen bacterium Fibrobacter succinogenes S85 was examined. Condensed tannins inhibited endoglucanase activity in the extracellular culture fluid, at concentrations as low as 25 μg ml-1. In contrast, cell-associated endoglucanase activity increased in concentrations of condensed tannins between 100 and 300 μg ml-1. Inhibition of endoglucanase activity in both the extracellular and the cell-associated fractions was virtually complete at 400 μg of condensed tannins ml-1. Despite the sharp decline in extracellular endoglucanase activity with increasing concentrations of condensed tannins, filter paper digestion declined only moderately between 0 and 200 μg of condensed tannins ml-1. However, at 300 μg ml-1, filter paper digestion was dramatically reduced and at 400 μg ml-1, almost no filter paper was digested. F. succinogenes S85 was seen to form digestive grooves on the surface of cellulose, and at 200 μg ml-1, digestive pits were formed which penetrated into the interior of cellulose fibers. Cells grown with condensed tannins (100 to 300 μg ml-1) possessed large amounts of surface material, and although this material may have been capsular carbohydrate, its osmiophilic nature suggested that it had arisen from the formation of tannin-protein complexes on the cell surface. The presence of electron-dense extracellular material suggested that similar complexes were formed with extracellular protein. Images

Effects of Condensed Tannins on Endoglucanase Activity and Filter Paper Digestion by Fibrobacter succinogenes S85.

https://people.uleth.ca/~selibl/Brentspapers/AnaerobeReview.pdf

The rumen: a unique source of enzymes for enhancing livestock production.

The rate and extent of degradation of plant structural tissues during digestion depends on a combination of animal, plant, and microbial factors. The major animal effect is the nature of the digestive tract itself. Ruminants with pregastric ruminai fermentation generally have a lower rate of passage than is seen in monogastric animals, and rumination (regurgitation and remastication) of large particles permits them to macerate fibrous materials more completely than do monogastric animals. Ruminants are thus more efficient at digesting fibrous plant material than are monogastric animals, in which fermentation occurs only in the large intestine. In contrast to ruminants, monogastric animals often tend to consume more readily digestible feeds. For example, cereals are a major component of the diets commonly fed to domestic animals. Thus, there is often a quantitative compositional difference in the substrates available to the digestive microbiota present in ruminants and monogastric animals. Cellulolytic organisms which are of pivotal importance in the rumen are generally viewed to have a lesser role than other fermentative organisms in the postgastric intestinal fermentation of domestic animals; however, there are exceptions — for example, the horse. Undoubtedly the presence or absence of particular gut species is directly related to the diet consumed and the retention time of the system.

K.-J. Cheng

Papers

Effects of Sainfoin (Onobrychis viciifolia Scop.) Condensed Tannins on Growth and Proteolysis by Four Strains of Ruminal Bacteria

Effects of Condensed Tannins on Endoglucanase Activity and Filter Paper Digestion by Fibrobacter succinogenes S85.

The rumen: a unique source of enzymes for enhancing livestock production.

Polysaccharide Degradation in the Rumen and Large Intestine

Stability of exogenous polysaccharide-degrading enzymes in the rumen