Microbes in Our Daily Lives
Learning Objectives
At the completion of this section the student should be able to:
- List several ways in which microbes benefit people
- Define 'normal flora' or' normal microbiota', biofilm
- Define infectious disease and differentiate this from disease
- Give examples of emerging infectious diseases
Microbes are everywhere in nature. They play an essential role in many aspects of the environment and in human health. The study of microbes and their interactions is called microbial ecology.
Sergei Winogradsky and Martinus Beijerinck were the first microbial ecologists. They studied the role microbes played in the cycling of nutrients in the biosphere. Although we don't think about it very much, the Earth is like a giant terrarium. We get a constant input of energy from the sun, but for the most part all of the elements on Earth today were here at the very beginnings of the Earth's formation. The water molecules in the coffee you drank today, could have been in the urine of a dinosaur 400 million years ago.... For an even more disgusting example, consider all of the road kill you have seen in your lifetime. Now consider what would happen if microbes did not degrade that organic material through decay processes. We would be up to our eyeballs in dead animals. Microbes recycle these organic compounds. They breakdown organic molecules to their fundamental parts. These parts are then available to be reassembled into new molecules. The elements are the same, they just are cycled from one compound to another. Microbes play a critical role in this cycling. They take the wood in that tree that fell in the storm and break it down to carbon dioxide which is released into the air and other elements that are deposited in the soil. Once in the air the CO2 can be taken in by a plant to form sugars, which in turn can be eaten by someone else. Microbes play an essential role in cycling not only carbon, but nitrogen, sulfur and phosphorus.
The natural ability of microbes to degrade compounds has been exploited effectively in a number of ways to benefit people. Sewage treatment is one example. Effective water and sewage treatment is necessary for the health and well being of society. Sewage treatment is a multi-step process that involves physical removal of large or recalcitrant solids and the biological digestion of organic materials. The biological digestion of organics occurs under aerobic and anaerobic conditions and ultimately produces an effluent that is low in organic content and microbial load. By-products of the process include methane gas which is used in some communities to power the treatment plant and fertilizer (Milorganite) can be made from the composted solids left over from the entire process.
Bioremediation
involves using microbes or their enzymes to remediate (correct fault or deficiency) soil, water, air, or clothing. Bioremediation is used to clean up oil spills, chemical spills, toxic waste sites and stained clothing. Bacteria and their enzymes can be thought of as nature's cleansers. Bacteria can also be used as natural pesticides. Bacillus thuringiensis in powdered form can be used to coat seeds or sprinkled on the leaves of plants. The bacteria begin replicating once they are ingested by plant pests (caterpillars and boring insects) eating the plant leaves. They then produce a toxic protein that kills the plant pest. The bacteria are not harmful to people and are not residual in the environment like chemical pesticides.
One of the first things babies do after being born is cry and lick their lips. That is their first taste of their new world and their first exposure to bacteria. The uterus is a sterile environment with respect to bacteria and microbes. Studies have shown that the bacteria in a woman's vagina experience explosive growth in the 48 hours before delivery. The organisms in the vaginal flora once swallowed are the first to colonize the baby's gut. Throughout our lifetimes we acquire microbes that live in us and on our body surfaces. These organisms make up our natural flora or normal microbiota. We need them to maintain our health. They take up space which prevents pathogens from colonizing the same space, they produce compounds that inhibit other organisms and in some cases they produce essential nutrients, like vitamin K, that they "share" with us. Vitamin K is produced by E. coli a natural inhabitant of our colon. When we remove our normal flora, we diminish our resistance to infection and open ourselves up to illness.
Bacteria in the real world are found growing as biofilms. A biofilm is a mixture of many different types of bacteria or microbes that share a surface. Dental plaque is one example. Dental plaque is composed of a bacterial community and the ions they precipitate around themselves. Biofilms benefit the community members by providing a substrate on which the organisms grow, they can protect the community from antibiotics or antiseptics and can allow community members to the share nutrient resources. Biofilms can be beneficial or deleterious to health. Biofilms of normal microbiota protect human tissue. However, pathogens can also produce biofilms and thrive on medical implements and prostheses.
