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  Normal flora  

Microorganisms, microbes and 鈥檅easties鈥欌Introduction to microbes (extract from "And You Thought You Werr Safe")
What are these little creatures that have such an impact on our world? We cannot see them, so they must be either a myth, or extremely small in size. Well, the latter is true. Microorganisms are organisms so small that we cannot see them with the unaided eye. To see a microorganism we need a viewing system such as a microscope in order to magnify them. Microorganisms are things such as bacteria, fungi, viruses, protozoa and algae.
The term microbe is nearly synonymous with microorganism. The difference being the term microbe is used more for living microorganisms such as bacteria, protozoa and fungi. Didn鈥檛 we already say that bacteria, fungi and protozoa were microorganisms? You are right, they are. However, did you notice that viruses were not included in the list? Viruses are what we call nonliving. Although viruses are categorised as nonliving, they still cause substantial morbidity (sickness) and mortality (death) through their own mechanisms.

To be categorized as living, an entity has to be able to perform certain criteria such as eating, growth, reproduction and death. Viruses do not grow or eat. They can remain inert for thousands of years in a closed or sealed room (e.g., a tomb), or on a calm surface until disturbed by an air current, sweeping them into the air and enabling them to be inhaled, or even touched by an unsuspecting individual. Depending in the virus, contact with enough of these infectious entities may result in disease or even death in certain circumstances. Instead of undergoing the process of physical growth as compared to humans and other animals, viruses are just produced in an "assembly line" fashion in our cells. Once a virus enters a human cell, the virus uses this cell as its host. Our cells act as "factories" for viruses, allowing them to replicate within the intracellular environment. A virus can "force" a host cell to build thousands of viral copies before the cell is damaged or destroyed. Since a virus forces the cell to replicate or reproduce copies of the original virus, it satisfies the criteria of reproduction. And because a virus is assembled in a host cell, but does not grow in size (once it is assembled, it is what we would define as adult size), viruses do not meet the criteria for growth. Because viruses do meet some of the criteria of living organisms, we categorize them between living and nonliving. However, they are still microorganisms, considering we cannot see them with the unaided eye.

Microorganisms, microbes and 鈥檅easties鈥
Introduction to microbes (extract from "And You Thought You Werr Safe")

As a matter of fact, viruses are about the smallest of the microorganisms. And because a virus is so small, it can gain entry into our cells and even into bacteria. A virus cannot replicate by itself. It needs a host cell, which is forced to function as a 鈥檉actory鈥 to produce viral copies. During the process of reproduction, many copies of a single virus type are replicated in a host cell. Once the host cell produces enough copies, it may burst only to release the newly made viruses to infect adjacent cells. From subsequent rupture and release of the newly formed viruses, the host cell dies. Alternatively, the host cell may not die. Some host cells simply keep manufacturing and "shedding" viral particles into the extracellular environment. The newly released viral particles then have the opportunity to infect adjacent cells of the particular tissue. During this process many cells may become infected from the replicated viruses and the cycle repeats itself continually until the infection is resolved by the immune system. Although, viral resolution is common, it is not guaranteed. Many viruses have the ability to establish permanent residency. These infections become latent and may later undergo periods of reactivation and remission, causing different degrees of illness throughout the lifetime of the infected individual.
There is only one group of infection causing entities smaller in size than viruses. These are called prions and are discussed in the following chapters. Prions are protein-containing particles, and are what we believe to be the etiological agent causing the neurodegenerative diseases BSE, CJD and others.
Microorganisms such as bacteria, fungi, and protozoa, can cause tissue damage through direct invasion of human tissues, liberation of toxins and enzymes, and by causing host mediated responses such as inflammation. As we shall see, some microorganisms can also find their way into individual cells, similar in mechanism to the virus.
Microbiology, on the other hand, is a branch of science dedicated to studying these microorganisms. And logically, medical microbiology is the study of microorganisms capable of causing human disease. On occasion we shall refer to microorganisms and microbes as "beasties". We do this, to help us keep in mind the ferocity of these little creatures.
Bio-warfare! Animals have been using Bacteria as weapons for hunting and survival, long before we conceived the thought. In a remote part of Indonesia live the Komodo Dragons. The Komodo Dragons grow to a length of nearly three meters and are speedy predators, running as fast as a dog. When the Komodo is young it feeds on small lizards, rodents and birds. As they grow, they graduate to feeding on larger animals, and even adults of their own species if they have the opportunity.
The Komodo Dragon has several virulent types of bacteria in its mouth which are lethal if they get into a victims blood. On many occasion, it is not the teeth of the Komodo鈥檚 bite which kills its鈥 victim, but rather the bacterial infection caused by the bite. The Komodo need only bite its prey once, follow it for a few days until the victim dies of septicaemia and then consume the deceased prey.
Komodo Dragons can bite each other, but are not affected. Through a unique relationship developed over time, Komodo Dragons have acquired a resistance to their own bacteria. Scientists culture many of the species of bacteria in the Komodo in hopes of creating new and effective antibiotics.
鈥橫icrobes only want a free meal鈥
While you read, try to keep in mind that these 鈥檅easties鈥 are not intentionally plotting our destruction. In the case of many bacteria and fungi, they inhabit us as "accidental tourists" and flourish on and within us, obtaining nutrients from our metabolism. Microbes are merely perpetuating their species and the meeting between 鈥檛hem鈥 and 鈥檜s鈥 is purely coincidental. Microbes cannot think or plot. Think of microbes as little machines that will begin to digest and break down any living tissue that you place them on. If conditions are not right (low temperatures) bacteria and fungi will lie patiently in a dormant state until the time is right. They have no appointments, no schedule. They will wait. And this can be hundreds to thousands of years. When suitable conditions arise, they will begin digesting their food source, multiplying in the process, until full decomposition occurs. These micro-machines are an invaluable part of the food chain and every ecosystem. By breaking down organic matter, bacteria and fungi ultimately return nutrients into the soil for plants and other microbes to feed on. It鈥檚 a never- ending cycle essential to our survival. On the other hand, an accidental liaison with the wrong microbe can be disastrous for us as well.
Microbes at work
Aside from being an invaluable component in every ecosystem, man uses microbes for many industrial purposes. Antibiotics used in medicine for the treatment of bacterial infections are the products of microbes. Drugs and other medicinal products can also be produced with the assistance of microbes in well-controlled environments. Many of our favourite beverages including beers and wine are created with the chemical machinery of microbes. The variety of well-known cheese, Blue Stilton (pictured below), is made from curds (solids) of fermented milk, separated from the whey (liquid), salted, and then pressed into blocks. Cheese is ripened with bacteria or fungi. Penicillin moulds are injected into Blue Stilton. The different microbes used, create different by-products, giving a cheese its distinctive flavour. We entitle the microbes to a free meal by inoculating the milk and cheese

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