WHAT IS MICROBIOLOGY? Microbiology is the study of very small living organisms – organisms called microorganisms or microbes. Microorganisms that cause disease are called pathogens. Microorganisms that do not cause disease are called nonpathogens.
WHY STUDY MICROBIOLOGY? 1. We have, living on and in our bodies, indigenous microflora (or indigenous microbiota) and, for the most part, they are beneficial to us.
2. Some of the organisms that colonize our bodies are known as opportunistic pathogens. Although such organisms do not usually 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.
3. Microorganisms are essential for life on this planet. For example, some microbes produce oxygen by the process known as photosynthesis.
4. Many microorganisms are involved in the decomposition of dead organisms and the waste products of living organisms. They are referred to as decomposers or saprophytes.
5. Some microorganisms are capable of decomposing industrial wastes (oil spills, for example). This is called bioremediation.
6. Many microorganisms are involved in elemental cycles. The study of the relationships between microbes and the environment is called microbial ecology.
7. Algae and bacteria serve as food for tiny animals. Tiny marine plants and algae are called phytoplankton, whereas tiny marine animals are called zooplankton.
8. Some microorganisms 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.
9. Many microorganisms are essential in food and beverage industries. The use of microorganisms in industry is called biotechnology.
10. Some bacteria and fungi produce antibiotics that are used to treat patients with infectious diseases. 11. Microbes are essential in the field of genetic engineering.
12. Microbes have been used as “cell models.” The more that scientists learned about the structure and functions of microbial cells, the more they learned about cells in general.
13. Microorganisms cause two categories of diseases: infectious diseases and microbial intoxications. An infectious disease results when a pathogen colonizes the body and subsequently causes disease. A microbial intoxication results when a person ingests a toxin that has been produced by a microorganism.
PIONEERS IN THE SCIENCE OF MICROBIOLOGY 1. Anton van Leeuwenhoek (1632-1723) >He is referred to as the “Father of Microbiology.” > At various times in his life he was a fabric merchant, a surveyor, a wine assayer, and a minor city official in Delft, Holland.
>He created what today are known as single-lens microscopes or simple microscopes. >In many specimens he observed a variety of tiny living creatures, which he called “animalcules.”
>The idea that life can arise spontaneously from nonliving material is called the theory of spontaneous generation or abiogenesis. >This theory was debated and tested from 1650 to 1850.
>Louis Pasteur and John Tyndall finally disproved the theory of spontaneous generation and proved that life can only arise from preexisting life. >This is called the theory of biogenesis, first proposed by a German scientist named Rudolf Virchow in 1858.
2. Louis Pasteur (1822-1895) >A French chemist, Pasteur discovered what occurs during alcoholic fermentation. >Through his experiments, Pasteur dealt the fatal blow to the theory of spontaneous generation.
>Pasteur discovered forms of life that could exist in the absence of oxygen. >Pasteur developed a process (today known as pasteurization) to kill microbes that were causing wine to spoil.
>Pasteur discovered the infectious agents that caused the silkworm diseases that were crippling the silk industry in France. >Pasteur made significant contributions to the germ theory of disease-the theory that specific microorganisms cause specific infectious diseases.
>Pasteur championed changes in hospital practices to minimize the spread of disease by pathogens. >Pasteur developed vaccines to prevent chicken cholera, anthrax, and swine erysipelas (a skin disease).
>Pasteur developed a vaccine to prevent rabies in dogs and successfully used the vaccine to treat human rabies.
3. Robert Koch (1843-1910) >A German physician, Koch made many significant contributions to the germ theory of disease. He proved that Bacillus anthracis was truly the cause of anthrax.
>Koch discovered that Bacillus anthracis produces spores, capable of resisting adverse conditions. >Koch developed methods of fixing, staining, and photographing bacteria.
>Koch developed methods of cultivating bacteria on solid media-the Petri dish in which to culture bacteria on solid media, and agar (a polysaccharide obtained from seaweed) as a solidifying agent. These methods enabled Koch to obtain pure cultures of bacteria.
The term pure culture refers to a condition in which only one type of organism is growing on a solid culture medium or in a liquid culture medium in the laboratory; no other types of organisms are present.
>Koch discovered the bacterium (Mycobacterium tuberculosis) that causes tuberculosis and the bacterium (Vibriocholerae) that causes cholera. >Koch’s work on tuberculin (a protein derived from M. tuberculosis) ultimately led to the development of a skin test valuable in diagnosing tuberculosis.
Koch’s Postulates An experimental procedure that proves a specific microorganism is the cause of a specific infectious disease. 1. A particular microorganism must be found in all cases of the disease and must not be present in healthy animals or humans.
2. The microorganism must be isolated from the diseased animal or human and grown in pure culture in the laboratory. 3. The same disease must be produced when microorganisms from the pure culture are inoculated into healthy susceptible laboratory animals.
4. The same microorganism must be recovered from the experimentally infected animals and grown again in pure culture.
EXCEPTIONS TO KOCH’S POSTULATES 1. Certain pathogens will not grow in or on artificial media in the laboratory (in vitro). Such pathogens include viruses, rickettsias, chlamydias, and the bacteria that cause leprosy and syphilis.
2. Many pathogens are species-specific, meaning that they infect only one species of animal. For example, some pathogens that infect humans will only infect humans. Because human volunteers are difficult to obtain and ethical reasons limit their use, the researcher may only be able to observe the changes caused by the pathogen in human cell cultures.
3. Synergistic infections, which are caused by the combined effects of two or more different microorganisms, are very difficult to reproduce in the laboratory.
4. Certain pathogens become altered when grown in vitro. Some become less pathogenic, whereas others become nonpathogenic. Thus, they will no longer infect animals after being cultured on artificial media.