Introduction to Microbiology

Microbiology

• It is a specialized science, handling the study of microorganisms.

Microorganisms

• The organisms and acellular entities are too small to be seen by the unaided eye, typically less than 1 mm, though some can be macroscopic.
• These organisms are relatively simple in their construction and do not have highly differentiated cells and distinct tissues.
• They are ubiquitous and represent the most populous and diverse group of organisms, found everywhere on the planet.
• They play a major role in recycling essential elements.
• Some are sources of nutrients and carry out photosynthesis.
• Microorganisms benefit society by the production of food, beverages, antibiotics, and vitamins.
• Others cause disease in plants and animals, food spoilage, poisoning, and intoxication.

Science of Microbiology

• It is about understanding the living world of microscopic organisms including microbial cells, diversity, evolution, and activities.
• It involves applying the understanding of microbial life processes for the benefit of mankind and the planet.

Microbial Cells

• Prokaryotic cells lack a true membrane-delimited nucleus.
• Eukaryotic cells have a membrane-enclosed nucleus, are more complex morphologically, and are usually larger than prokaryotic cells.

Organisms and Biological Entities Studied by Microbiologists can be Cellular or Acellular

• Cellular entities include fungi (e.g., Yeasts, Molds), protists (e.g., Algae, Protozoa, Slime molds), bacteria (e.g., Escherichia coli), and archaea (e.g., Methanogens).
• Acellular entities include viruses, viroids, satellites which are composed of protein and nucleic acids and RNA respectively, and prions which are infectious proteins.

Acellular Infectious Agents

• Viruses are the smallest of all microbes, require a host cell to replicate, and can cause a range of diseases, including some cancers.
• Viroids and virusoids: infectious agents composed of RNA.
• Prions: infectious proteins.

Discovery of Microorganisms

• Robert Hooke (1635-1703), reported that living things were composed of little boxes or cells, and illustrated the fruiting structures of molds, providing the first description of microorganisms.
• Antony van Leeuwenhoek (1632-1723) was the first person to accurately observe and describe microorganisms.
• Ferdinand Cohn (1828–1898) discovered bacterial endospores, extremely heat-resistant forms of bacteria, laid the groundwork for a system of bacterial classification, and introduced the use of cotton for closing flasks and tubes.

The Conflict Over Spontaneous Generation

• Spontaneous generation is the idea that living organisms can develop from nonliving or decomposing matter.
• Francesco Redi (1626-1697) discredited spontaneous generation by showing that maggots on decaying meat came from fly eggs.
• John Needham (1713-1781), through his experiment involving boiled mutton broth in a sealed flask that became cloudy and contained microorganisms, suggested that organic matter in the extract contained a "vital force" that confers the properties of life on nonliving matter.
• Lazzaro Spallanzani (1729-1799) disproved the spontaneous generation theory by using broth in flasks sealed and boiled which yielded no growth of microorganisms and proposed that air carried germs to the culture medium and heating the air in the sealed flask destroyed its ability to support life.
• John Tyndall (1820-1893) demonstrated that dust carries microorganisms and if dust was absent, nutrient broths remained sterile.
• He also provided evidence for the existence of exceptionally heat-resistant forms of bacteria.
• Louis Pasteur (1822-1895) in his 'Swan-neck flask' experiments placed nutrient solution in flasks, created flasks with long, curved necks, boiled the solutions, and left flasks exposed to air ultimately yielding no growth of microorganisms.

Role of Microorganisms in Disease

• Was not immediately obvious, infectious disease was believed to be due to supernatural forces or imbalances of 4 bodily-fluid 'humors'.
• Establishing connection depended on development of techniques for studying microbes.
• Agostini Bassi (1773-1856) displayed that a disease of silkworms was induced by a fungus.
• M. J. Berkeley (ca. 1845) demonstrated that Great Potato Blight of Ireland was led by a water mold.
• Heinrich de Bary (1853) displayed that smut and rust fungi induced cereal crop diseases.
• Louis Pasteur demonstrated microorganisms induce fermentation, helping French wine industry, developed pasteurization to avoid wine spoilage by microbes, and showed that pébrine disease of the silkworms was induced by a protozoan.
• Joseph Lister provided indirect evidence that microorganisms were the causal agents of disease, developed a system of surgery designed to prevent microorganisms from entering wounds as well as methods for treating instruments and surgical dressings, which led to his patients having fewer postoperative infections.
• Robert Koch (1843-1910) established the relationship between Bacillus anthracis and anthrax and used criteria developed by his teacher Jacob Henle (1809-1895), these criteria known as Koch's postulates which are still used today to establish the link between a particular microorganism and a particular disease.

Koch’s Postulates

• The microorganism must be present in every case of the disease but absent from healthy organisms.
• The suspected microorganisms must be isolated and grown in pure culture.
• The same disease must result when the isolated microorganism is inoculated into a healthy host.
• The same microorganisms must be isolated again from the diseased host.

Limitations of Koch's Postulates

• Some organisms cannot be grown in pure culture.
• Using humans in completing the postulates is unethical.
• Molecular and genetic evidence may replace and overcome these limits.

Development of Techniques for Studying Microbial Pathogens

• Koch's work led to the discovery or development of agar, Petri dishes, nutrient broth and nutrient agar, and methods for isolating microorganisms.

Other Developments

• Charles Chamberland (1851-1908) developed porcelain bacterial filters used by Ivanoski and Beijerinck to study tobacco mosaic disease, determined extracts from diseased plants had infectious agents present which were smaller than bacteria and passed through the filters and infectious agents were eventually shown to be viruses.
• Pasteur and Roux discovered that incubation of cultures for long intervals between transfers caused pathogens to lose their ability to cause disease (termed 'attenuation') and called attenuated bacteria a vaccine (Latin vacca, cow) in honor of Edward Jenner.
• Pasteur and his coworkers developed vaccines for chicken cholera, anthrax, and rabies.

Immunological Studies

• Were once established and led to the study of host defenses (immunology).
• Edward Jenner (ca. 1798) used a vaccination procedure to protect individuals from smallpox.

More Developments

• Emil von Behring (1854-1917) and Shibasaburo Kitasato (1852-1931) developed antitoxins for diphtheria and tetanus which provided evidence for humoral (antibody-based) immunity.
• Elie Metchnikoff (1845-1916) discovered bacteria-engulfing, phagocytic cells in the blood which provided evidence for cellular immunity.

Development of Industrial Microbiology and Microbial Ecology

• Louis Pasteur demonstrated that alcohol fermentations and other fermentations were the result of microbial activity, and developed the process of pasteurization to preserve wine during storage.

Developments in Microbial Ecology

• Sergei Winogradsky (1856-1953) and Martinus Beijerinck (1851-1931) studied soil microorganisms and discovered numerous interesting metabolic processes (e.g., nitrogen fixation), and pioneered the use of enrichment cultures and selective media.