Why We Need Study About Microbes (Microbiology)?

Although they are very small, microbes play significant roles in our lives. Listed below are a few of the many reasons to take a microbiology course and to learn about microbes:
  • We have, living on and in our bodies (e.g., on our skin and in our mouths and intestinal tract), approximately 10 times as many microbes as the total number of cells (i.e., epithelial cells, nerve cells, muscle cells, etc.) that make up our bodies (10 trillion cells x 10 = 100 trillion microbes). It has been estimated that perhaps as many as 500 to 1,000 different  species of microbes live on and in us. Collectively, these microbe's are known as our indigenous microbiota (or human microbiome or human bioneme) and, for the most part, they are of benefit to us. For example, the indigenous microbiota inhibit the growth of pathogens in those areas of the body where they live by occupying space, depleting the food supply, and secreting materials (waste products, toxins, antibiotics, etc.) that may prevent or reduce the growth of pathogens.
  • Some of the microbes that colonize (inhabit) our bodies are known as opportunistic pathogens (or opportunists). Although these microbes usually do not cause us any problems, they have the potential to cause infections if they gain access to a part of our anatomy where they do not belong. For example, a bacterium called Escherichia coli (E. coli) lives in our intestinal tracts. This organism does not cause us any harm as long as it remains in our intestinal tract, but can cause disease if it gains access to our urinary bladder, bloodstream, or a wound. Other opportunistic pathogens strike when a person becomes run-down, stressed out, or debilitated (weakened) as a result of some disease or condition. Thus, opportunistic pathogens can be thought of as microbe's awaiting the opportunity to cause disease.
  • Microbes are essential for life on this planet as we know it. For example, some microbes produce oxygen by the process known as photosynthesis. Actually, microbes contribute more oxygen to our atmosphere than do plants. Thus, organisms that require oxygen—humans, for example—owe a debt of gratitude to the algae and cyanobacteria (a group of photosynthetic bacteria) that produce oxygen.
  • Many microbes are involved in the decomposition of dead organisms and the waste products of living organisms. Collectively, these microbes are referred to as decomposers or saprophytes. Decomposition is the process by which substances are broken down into simpler forms of matter. By definition, a saprophyte is an organism that lives on dead or decaying organic matter. Imagine living in a world with no decomposers. Not a pleasant thought! Saprophytes aid in fertilization by returning inorganic nutrients to the soil. They break down dead and dying organic materials (plants and animals) into nitrates, phosphates, and other chemicals necessary for the growth of plants (Fig. 1).
    Saprophytes. Saprophytes break down dead and decaying organic material into inorganic nutrients in the soil.
    Fig. 1: Saprophytes. Saprophytes break down dead and decaying organic material into inorganic nutrients in the soil.
  • Some microbes are capable of decomposing industrial wastes (oil spills, for example). Thus, we can use microbes—genetically engineered microbes, in some cases—to clean up after ourselves. The use of microbes in this manner is called bioremediation.
  • Many microbes are involved in elemental cycles, such as the carbon, nitrogen, oxygen, sulfur, and phosphorous cycles. In the nitrogen cycle, certain bacteria convert nitrogen gas in the air to ammonia in the soil. Other soil bacteria then convert the ammonia to nitrites and nitrates. Still other bacteria convert the nitrogen in nitrates to nitrogen gas, thus completing the cycle (Fig. 2). Knowledge of these microbes is important to farmers who practice crop rotation to replenish nutrients in their fields and to gardeners who keep compost pits as a source of natural fertilizer. In both cases, dead organic material is broken down into inorganic nutrients (e.g., nitrates and phosphates) by microbes. The study of the relationships between microbes and the environment is called microbial ecology.
    Nitrogen fixation. Nitrogen-fixing bacteria that live on or near the roots of legumes convert free nitrogen from the air into ammonia in the soil. Nitrifying bacteria then convert the ammonia into nitrites and nitrates, which are nutrients used by plants.
    Fig.2: Nitrogen fixation. Nitrogen-fixing bacteria that live on or near the roots of legumes convert free nitrogen from the air into ammonia in the soil. Nitrifying bacteria then convert the ammonia into nitrites and nitrates, which are nutrients used by plants.
  • Algae and bacteria serve as food for tiny animals.Then, larger animals eat the smaller creatures, and so on. Thus, microbes serve as important links in food chains (Fig. 3). Microscopic organisms in the ocean, collectively referred to as plankton, serve as the starting point of many food chains. Tiny marine plants and algae are called phytoplankton, whereas tiny marine animals are called zooplankton.
    Food chain. Tiny living organisms such as bacteria, algae, microscopic aquatic plants (e.g., phytoplankton), and microscopic aquatic animals (e.g., zooplankton) are eaten by larger animals, which in turn are eaten by still larger animals, etc., until an animal in the chain is consumed by a human. Humans are at the top of the food chain.
    Fig.3: Food chain. Tiny living organisms such as bacteria, algae, microscopic aquatic plants (e.g., phytoplankton), and microscopic aquatic animals (e.g., zooplankton) are eaten by larger animals, which in turn are eaten by still larger animals, etc., until an animal in the chain is consumed by a human. Humans are at the top of the food chain.
  • Some microbes live in the intestinal tracts of animals, where they aid in the digestion of food and, in some cases, produce substances that are of value to the host animal. For example, the E. coli bacteria that live in the human intestinal tract produce vitamins K and B1, which are absorbed and used by the human body. Although termites eat wood, they cannot digest wood. Fortunately for them, termites have cellulose-eating protozoa in their intestinal tracts that break down the wood that the termites consume into smaller molecules that the termites can use as nutrients.
  • Many microbes are essential in various food and beverage industries, whereas others are used to produce certain enzymes and chemicals (Table 1-2). The use of living organisms or their derivatives to make or modify useful products or processes is called biotechnology.
    Table 1-2 Products Requiring Microbial Participation in the Manufacturing Process
    Table 1-2 Products Requiring Microbial Participation in the Manufacturing Process
  • Some bacteria and fungi produce antibiotics that are used to treat patients with infectious diseases. By definition, an antibiotic is a substance produced by a microbe that is effective in killing or inhibiting the growth of other microbes. The use of microbes in the antibiotic industry is an example of biotechnology.
  • Microbes are essential in the field of genetic engineering. In genetic engineering, a gene or genes from one organism (e.g., from a bacterium, a human, an animal, or a plant) is/are inserted into a bacterial or yeast cell. Because a gene contains the instructions for the production of a gene product (usually a protein), the cell that receives a new gene can now produce whatever product is coded for by that gene; so too can all of the cells that arise from the original cell. Microbiologists have engineered bacteria and yeasts to produce a variety of useful substances, such as insulin, various types of growth hormones, interferons, and materials for use as vaccines.
  • For many years, microbes have been used as “cell models.” The more the scientists learned about the structure and functions of microbial cells, the more they learned about cells in general. The intestinal bacterium E. coli is one of the most studied of all microbes. By studying E. coli, scientists have learned a great deal about the composition and inner workings of cells, including human cells.
    The two categories of diseases caused by pathogens. Infectious diseases result when a pathogen colonizes (inhabits) the body and subsequently causes disease. Microbial intoxications result when a person ingests a toxin (poisonous substance) that has been produced by a pathogen in vitro (outside the body). MRSA, methicillin-resistant Staphylococcus aureus.
    Fig. 4: The two categories of diseases caused by pathogens. Infectious diseases result when a pathogen colonizes (inhabits) the body and subsequently causes disease. Microbial intoxications result when a person ingests a toxin (poisonous substance) that has been produced by a pathogen in vitro (outside the body). MRSA, methicillin-resistant Staphylococcus aureus.
  • Finally, we come to diseases. Microbes cause two categories of diseases: infectious diseases and microbial intoxications (Fig. 4). An infectious disease results when a pathogen colonizes the body and subsequently causes disease. A microbial intoxication results when a person ingests a toxin (poisonous substance) that has been produced by a microbe. Of the two categories, infectious diseases cause far more illnesses and deaths. Infectious diseases are the leading cause of death in the world and the third leading cause of death in the United States (after heart disease and cancer). Worldwide, infectious diseases cause about 50,000 deaths per day, with the majority of deaths occurring in developing countries. Anyone pursuing a career in a healthcare profession must be aware of infectious diseases, the pathogens that cause them, the sources of the pathogens, how these diseases are transmitted, and how to protect yourself and your patients from these diseases. Physicians’ assistants, nurses, surgical technologists, dental assistants, laboratory scientists, respiratory therapists, orderlies, nurses’ aides, and all others who are associated with patients and patient care must take precautions to prevent the spread of pathogens. Harmful microbes may be transferred from healthcare workers to patients; from patient to patient; from contaminated mechanical devices, instruments, and syringes to patients; from contaminated bedding, clothes, dishes, and food to patients; and from patients to healthcare workers, hospital visitors, and other susceptible persons. To limit the spread of pathogens, sterile, aseptic, and antiseptic techniques are used everywhere in hospitals, nursing homes, operating rooms, and laboratories. In addition, the bioterrorist activities of recent years serve to remind us that everyone should have an understanding of the agents (pathogens) that are involved and how to protect ourselves from becoming infected.
The microbes that live on and in the human body are referred to as our indigenous microbiota. Opportunistic pathogens do not cause disease under ordinary conditions, but have the potential to cause disease should the opportunity present itself. Pathogens cause two major types of diseases: infectious diseases and microbial intoxications.

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