Background:
Saccharomyces cerevisiae: Fungi make up one of the five kingdoms and as a kingdom it is divided into seven major phylums: Basidiomycota (“club fungi”), Ascomycota (“sac fungi”), Zygomycota (conjugation bacteria), Chytridiomycota, Blastidocladiomycota, Neocallimastigomycota, and fungal imperfecti [5]. Included amongst the lineage are mushrooms, rusts, smuts, puffballs, truffles, molds, and yeasts [3]. Fungi are more closely related to the Kingdom Animalia than the Kingdom Plantae as they were a part of the eukaryotic crown group that radiated off millions of years ago [3]. They digest organic material and the remnants are then in a form that may be digested by more complex organisms [10]. Fungi digest their food outside of their structures by secreting enzymes to the surrounding environment and then absorbing what they need [10], they live in their own food supply and simply grow to new areas when nutrition in their environment is low [3]. Most fungi grow as tubular filaments, hyphae, these then may form irregular interwoven masses called mycelium [8]. The walls of the hyphae are strengthened by chitin, a polymer of N-acetylglucosamine [8]. Fungi reproduce by releasing spores from the mycelium body into the air, these are then carried away where they will later settle and grow [10].
Saccharomyces cerevisiae are members of the Hemiascomycetae class of Ascomycota [10]. Ascomycota are classified by their reproduction as they release their spores into special pod-like structures called asci [10]. It is more commonly known as baker’s yeast or brewer’s yeast and holds extreme economic importance for its use in the production of alcohols and in the leavening of bread and other baked products [1]. It ferments sugars in the flour or added to the dough, giving off carbon dioxide and ethanol [12] and providing itself with two ATPs [13]. Saccharomyces has adapted the ability to break down materials through both aerobic and anaerobic environments and thus can survive in oxygen deficient systems for relatively short periods of time [13]. Thus they have been known to reside in a wide variety of habitats from the skin of grapes and other fruit to the intestinal tract of warm blooded animals [16].
Saccharomyces is a common laboratory organism because it is a unicellular organism whose cellular activities are more like our own than the most common E. coli bacterium [9]. Furthermore they grow rapidly, can be cultured easily, can be easily transformed (or given a foreign piece of DNA), and their entire genome is known [9]. It also has a place in agriculture as many cattle farmers supplement their cattle diets with Saccharomyces. Research has shown supplementation of the diet by S. cerevisiae has an auspicious effect not only on increased digestive efficiency but also increased immune system efficiency and decreased bacterial infections not only in ruminant but also monogastric species (like humans) [2]. They also have been shown to have a nutritive value in the system with their production of vitamins to be used by the organism [6]. In surveys done on yeast supplemented cattle: an increase by as much as 7.5%, even up to 13% in proper feed conditions, in live wait of beef cattle, depending on the type of diet supplemented with [6]. Furthermore, an improvement was made by about 4% of the milk yield in dairy cows, this type of improvement usually only being seen with an increased feed intake [2]. The apparent effects of diet supplementation by S. cerevisiae on monogastric species are stimulation of brush border disaccharides, anti-adhesive effects on pathogen, stimulation of non-specific immunity (immune system activation), toxin action inhibition, and antagonistic effect against pathogenic microorganisms [2]. More importantly, they are resistant to gastrointestinal passage, and thus they have the capability of moving through the system and being passed unbroken [6]. Furthermore, S. cerevisiae has an anti-adhesive affect on bacteria, this is due to the fact that the bacteria are more attracted to the sugar complexes present in the yeast cell wall [6]. As the Saccharomyces passes through the digestive system, unaltered, it collects E. coli and other harmful infectious bacteria and sticks to it [2]. Then the two pass harmlessly through the digestive tract as a bacteria-fungal complex [2].
Escherichia coli: Theodore Escherich first described E. coli in 1885 when he isolated it from feces of newborns and for much time, until it was found to be the cause of diarrhea infection in infants in 1935, it was thought to be only a commensal organism of the large intestine [14]. E. coli and its relatives are known as “enteric bacteria” because they live in the digestive tract, particularly the intestines, of humans and other animals [14]. In close relation to E. coli and among the enteric bacteria is Shigella, the bacterial cause of dysentery, and Salmonella [14]. E. coli is a member of the family Enterobacteriaceae: this family is made up of gram-negative, nonsporeforming, rod-shaped bacteria that are often mobilized by flagella [14]. They grow well either in presence or lack of oxygen and thus metabolism may either be by respiration or fermentation [14].
E. coli is a very versatile bacterium, in the laboratory it may grow with glucose as its only organic constituent and may still produce all of the molecular components to make up the cell [14]. Wild-type E. coli is even more versatile as it has no growth factor requirements and can even grow under anaerobic or aerobic conditions [14]. In its natural environment, as well as in the laboratory, E. coli can respond to changes in temperature, pH, osmolarity and others [14]. In response to changes to temperature and osmolarity the cell might regulate the diameter of pores [14]. It can open up pores to accommodate larger substances or tighten pores to exclude inhibitory substances, like bile salts [14]. In the presence or absence of gases around them, the cells may swim toward or away from them [14]. It may stop swimming altogether and grow fimbriae to attach itself to a surface to keep it from moving. E. coli may also survey the environmental contents and “decide” (determined actually by genes within the cell) which enzymes it needs to breakdown and use these available solutions [14]. E. coli will thus not produce enzymes it does not need and will always produce the ones it does [14].
Certain pathogenic strains of E. coli may cause food borne illnesses, a particularly dangerous type being enterohemorrhagic E. coli, or EHEC [7]. EHEC often causes bloody diarrhea and can lead to kidney failure in children or immunosuppressed and immunocompromised patients [7]. The most common pathogenic strain of E. coli in the United States (and the first one identified in the United States) is known as O157:H7; this strain produces many powerful toxins that may severely damage the lining of the intestine [4]. Others include O26:H11 and O111:H8. The major source of these pathogenic strains is in cattle but other domestic and wild animals may carry these bacteria in their digestive systems. The E. coli and its toxins are transmitted to humans in the following ways: undercooked or raw beef, salami. Alfalfa sprouts, lettuce, unpasteurized milk, apple juice and apple cider, contaminated well water, contaminated swimming pools, contaminated oceans and lakes. All of these means of transportation are by ingestion. Most common symptoms of infection with pathogenic E. coli are: nausea, severe abdominal cramps, watery or very bloody diarrhea, fatigue, and a low grade fever [7]. Enterotoxigenic E. coli (ETEC) can also cause diarrhea (particularly traveler’s diarrhea as they are most prevalent in developing third world countries) as they produce a toxin similar to the Cholera toxin [4]. Also Enterpathogenic E. coli are associated with prolonged diarrhea, lasting two weeks or more [4]. Antibiotics are usually not helpful with these kinds of infections because they are very harmful and yet very chronic, thus prevention, with proper diet supplementation should be a point of interest.
Probiotics: Probiotics are live microorganisms, in many cases bacteria and increasingly yeasts that are similar to, and therefore mimic the actions of, microorganisms already present in the human gastrointestinal tract. They therefore increase in the production of helpful products or the completion of necessary processes, making food passage and dietary consumption much smoother of a system. People use many probiotic substances in the prevention and treatment of many illnesses and many of these products are available over the counter at the drug store. However there is limited evidence supporting the use of probiotics and how to use it and the safety factors of certain proposed probiotics [15], thus must interest should be taken in the development of not only proper procedures and precautions but also general understanding of the basic processes of each different organism. The World Health Organization defines probiotics as, “live microorganisms, which, when administered in adequate amounts, confer a health benefit on the host," past this most scientists are unable to agree on what exactly probiotics are. Probiotics are available in foods and dietary supplements (capsules, tablets, powders) and other sources. Yogurt, fermented and unfermented milk and some juices are all examples of regular household foods with probiotic effects.
Some scientifically confirmed uses of probiotics include: to treat diarrhea (that provides the strongest area of evidence), to prevent and treat infections of the urinary tract or of the female genital tract, to treat irritable bowel syndrome, to reduce recurrence of bladder cancer, shorten the infection duration of Clostridium difficile, to prevent and treat pouchitis, and to prevent and manage atopic dermatitis (eczema) [15]. In a study done on Swedish employees, those who supplemented their diets with probiotics showed a decline in days absent to work and late, coinciding with a decrease in reported illness incidents [17]. However it is important to note that more research needs to be done in this area because researchers have also shown in studies of probiotics as cures any beneficial effect was low and there was high placebo phenomenon without a blind study [15].
Microorganisms exists naturally in the stomachs of all species, those that exist in cattle have the special task of breaking down the long carbohydrate chains of the grass that the cattle take in so much of. In agriculture, supplementation of cattle diets by probiotic microorganisms has become common place. Farmers try to aid their stock’s natural systems for processing food because the more efficiently the animal processes the food the more weight the animal packs on or the more milk she produces. Several microorganisms have, so far, been authorized as new additives in feed-stuffs: Bacillus cereus, Bacillus cereus toyoi, Bacillus licheniformus, Bacillus subtillis, Enterococcus faecium, Lactobacillus farmciminis, Pediococcus acidilactici, Saccharomyces cerevisisae [2]. All of these strains have demonstrated positive effects in different ruminant and monogastric species [2]. In beef cattle live weight of the cattle can increase by as much as 13% with dietary S. cerevisiae supplementation and 4% improvement can be seen in milk production of dairy cattle. All of these results are contingent upon the productive parameters (type of diet fed to cattle in addition to the probiotic) and sanitary conditions [2]. The most widely studied animal with respect to its response to probiotic diet supplementation is poultry [11]. The desired outcome would be the ability to control Salmonella through diet supplementation of the livestock’s feedstuffs. For these a Lactobacillus species was specifically selected to seek out and take inhibitory action against the Salmonella[11]. In many cases species are sought out that would have a competitive affect against the target species. For example, S. cerevisiae, when supplemented in the diet of cattle, has an inhibitory effect on the production of lactic acid by Streptococcus bovis because the Saccharomyces competes for the same food sources as the Streptococcus. The ultimate effect is the Saccharomyces has the power to stabilize the acidity of the ruminant stomach [2].
Further areas of interest involving probiotics in which researchers are involving themselves include: understanding the modes of action, or what is occurring on the molecular level? What interactions are taking place? What are ways that the microorganism’s beneficial effects could be protected through the preparation of food? How does the preparation of food to be simultaneously supplemented affect the probiotics’ effects on the digestive system? What are the best methods for administration, doses and supplementation?
