Introduction to Microbiology

Microbes in Our Lives

Microorganisms, or microbes, are organisms too small to be seen with the unaided eye. They play essential roles in ecosystems, industry, and human health.

• Pathogenic microbes cause diseases in humans, animals, and plants.

• Microbes decompose organic waste, recycling nutrients in the environment.

• They are producers in ecosystems, especially through photosynthesis.

• Microbes are used to produce industrial chemicals (e.g., ethanol, acetone), fermented foods (e.g., vinegar, cheese, bread), and products for manufacturing and medicine (e.g., insulin, vaccines).

Naming and Classifying Microorganisms

Scientific Nomenclature

The system of scientific nomenclature was established by Linnaeus. Each organism is given a two-part name: the genus and the specific epithet (species name).

• Scientific names are italicized or underlined; the genus is capitalized, and the specific epithet is lowercase (e.g., Escherichia coli).

• Names may be descriptive or honor a scientist.

• After the first use, names can be abbreviated (e.g., E. coli).

Example: Staphylococcus aureus describes clustered (staphylo-) spherical (cocci) cells with gold-colored (aureus) colonies.

Types of Microorganisms

Major Groups of Microbes

Microorganisms are classified into several major groups based on their cellular structure, metabolism, and genetics.

• Bacteria: Prokaryotic, peptidoglycan cell walls, reproduce by binary fission, use organic/inorganic chemicals for energy.

• Archaea: Prokaryotic, lack peptidoglycan, live in extreme environments (e.g., methanogens, extreme halophiles, thermophiles).

• Fungi: Eukaryotic, chitin cell walls, use organic chemicals, include multicellular molds/mushrooms and unicellular yeasts.

• Protozoa: Eukaryotic, absorb/ingest organic chemicals, may be motile via pseudopods, cilia, or flagella.

• Algae: Eukaryotic, cellulose cell walls, photosynthetic, produce oxygen and organic compounds.

• Viruses: Acellular, DNA or RNA core surrounded by protein coat (sometimes lipid envelope), replicate only in host cells.

• Multicellular Animal Parasites: Eukaryotic, include helminths (parasitic flatworms and roundworms), microscopic stages in life cycles.

Bacteria

• Prokaryotic cells with peptidoglycan cell walls.

• Reproduce by binary fission.

• Obtain energy from organic or inorganic chemicals.

Archaea

• Prokaryotic but lack peptidoglycan in cell walls.

• Often found in extreme environments (e.g., high salt, high temperature).

• Include methanogens, extreme halophiles, and extreme thermophiles.

Fungi

• Eukaryotic organisms with chitin cell walls.

• Use organic chemicals for energy.

• Molds and mushrooms are multicellular; yeasts are unicellular.

Protozoa

• Eukaryotic, absorb or ingest organic chemicals.

• Motile via pseudopods, cilia, or flagella.

Algae

• Eukaryotic, cellulose cell walls.

• Photosynthetic, produce oxygen and organic compounds.

Viruses

• Acellular, consist of DNA or RNA core surrounded by a protein coat (sometimes a lipid envelope).

• Replicate only inside living host cells.

Multicellular Animal Parasites

• Eukaryotic, include helminths (parasitic flatworms and roundworms).

• Microscopic stages in their life cycles.

Classification of Microorganisms

The Three-Domain System

Microorganisms are classified into three domains based on differences in cellular organization and genetics:

• Bacteria

• Archaea

• Eukarya (includes protists, fungi, plants, and animals)

Example: Eukarya includes protists, fungi, plants, and animals; Bacteria and Archaea are prokaryotic domains.

A Brief History of Microbiology

The First Observations

• 1665: Robert Hooke reported that living things are composed of cells.

• 1673–1723: Anton van Leeuwenhoek described live microorganisms.

• 1858: Rudolf Virchow proposed that cells arise from preexisting cells (cell theory).

Disproving Spontaneous Generation

Spontaneous generation was the hypothesis that living organisms arise from nonliving matter. The alternative, biogenesis, states that living organisms arise from preexisting life. Louis Pasteur's experiments with S-shaped flasks provided strong evidence against spontaneous generation.

• Pasteur's S-shaped flask allowed air in but kept microbes out, preventing contamination.

The Golden Age of Microbiology

Major Discoveries (1857–1914)

• Relationship between microbes and disease established.

• Development of immunity and antimicrobial drugs.

Fermentation and Pasteurization

• Fermentation: Conversion of sugar to alcohol by microbes (used in beer and wine production).

• Pasteurization: Application of high heat for a short time to kill spoilage microbes without evaporating alcohol.

Example: Pasteurization is used to make milk and wine safe for consumption.

The Germ Theory of Disease

• Microorganisms can cause disease.

• Agostino Bassi (1835): Fungus caused silkworm disease.

• Ignaz Semmelweis (1840s): Advocated handwashing to prevent puerperal fever.

• Joseph Lister (1860s): Used chemical disinfectants to prevent surgical wound infections.

Koch's Postulates

• Robert Koch (1876): Proved that a specific bacterium causes a specific disease (anthrax).

• Koch's postulates: Experimental steps to link a microbe to a disease.

Vaccination

• Edward Jenner (1796): Inoculated a person with cowpox virus, providing protection from smallpox.

• Vaccination derives from 'vacca' (cow); the protection is called immunity.

Modern Chemotherapy

• Chemotherapy: Treatment with chemicals (synthetic drugs or antibiotics).

• Antibiotics: Chemicals produced by bacteria and fungi that inhibit or kill other microbes.

The First Synthetic Drugs

• Quinine: Used to treat malaria.

• Paul Ehrlich (1910): Developed salvarsan, a synthetic arsenic drug for syphilis ('magic bullet').

• 1930s: Sulfonamides synthesized.

Discovery of Antibiotics

• Alexander Fleming (1928): Discovered penicillin produced by Penicillium fungus, which killed S. aureus.

• Penicillin was mass-produced and revolutionized medicine.

Modern Developments in Microbiology

Subfields of Microbiology

• Bacteriology: Study of bacteria

• Mycology: Study of fungi

• Virology: Study of viruses

• Parasitology: Study of protozoa and parasitic worms

• Immunology: Study of immunity

Recombinant DNA Technology

• Microbial genetics: Study of inheritance in microbes.

• Molecular biology: Study of how DNA directs protein synthesis.

• Genomics: Study of an organism's genes; aids in classification.

• Recombinant DNA: DNA made from two different sources (e.g., inserting animal DNA into bacteria).

Microbial Ecology and Bioremediation

• Bacteria recycle elements (carbon, nitrogen, sulfur, phosphorus).

• Bacteria degrade organic matter in sewage and detoxify pollutants (e.g., oil, mercury).

• Microbes can be used to control insect pests (e.g., Bacillus thuringiensis).

Biotechnology

• Use of microbes to produce foods, chemicals, and medicines.

• Recombinant DNA technology enables production of proteins, vaccines, and enzymes.

• Gene therapy: Replacing defective genes in human cells.

• Genetically modified bacteria protect crops from insects and freezing.

Normal Microbiota and Infectious Diseases

Normal Microbiota

• Microbes normally present in and on the human body are called normal microbiota.

• They prevent growth of pathogens and produce growth factors (e.g., folic acid, vitamin K).

Biofilms

• Microbes attach to solid surfaces and grow into masses (biofilms).

• Biofilms can form on rocks, pipes, teeth, and medical implants.

Emerging Infectious Diseases (EIDs)

• Diseases that are new or increasing in incidence.

• Examples: Avian influenza A, MRSA, West Nile encephalitis, Bovine spongiform encephalopathy, E. coli O157:H7, Ebola hemorrhagic fever, AIDS.

Summary Table: Major Groups of Microorganisms

Additional info: This summary integrates foundational concepts from the first chapter of a college-level microbiology course, including the history, classification, and importance of microorganisms, as well as key discoveries and applications in the field.