Introduction to Microbiology: The Microbial World and You

Introduction to Microbiology

Microbes in Our Lives

Microbiology is the study of microorganisms, which are organisms too small to be seen with the unaided eye. These include bacteria, viruses, fungi, protozoa, and algae. Microbes play essential roles in ecosystems and human health.

• Microorganisms: Organisms invisible to the naked eye.

• Germ: A non-specific term for rapidly growing cells, often used to describe microbes but more accurately refers to pathogens.

• Pathogen: A microorganism that causes disease in its host.

Microorganisms: Roles and Importance

Functions of Microorganisms

Microorganisms are vital for ecological balance and human industry. While some are pathogenic, most are harmless or beneficial.

• Decompose organic waste

• Producers in ecosystems via photosynthesis

• Industrial chemical production (e.g., ethanol, acetone)

• Fermentation of foods (e.g., vinegar, cheese, bread)

• Manufacturing and treatment products (e.g., insulin)

Pathogenic microbes are a minority; most microbes are harmless or beneficial.

Additional info: Microbes are used in biotechnology to produce medicines and food products, and play a role in nutrient cycling.

Knowledge of Microorganisms

Understanding microbes is crucial for disease prevention and laboratory safety.

• Prevents disease occurrence

• Enables aseptic techniques in medicine and research

Naming and Classifying Microorganisms

Scientific Naming

Linnaeus established binomial nomenclature, giving each organism a genus and species name (e.g., Homo sapiens).

• Genus: Capitalized and italicized/underlined

• Species: Lowercase and italicized/underlined

• Names may honor scientists or describe features (e.g., Staphylococcus aureus, Escherichia coli)

• Abbreviations: After first use, genus may be abbreviated (e.g., S. aureus, E. coli)

Additional info: Organisms in the same species share most characteristics.

Classification of Microorganisms

Three Domains of Life

Microorganisms are classified into three domains based on cell type:

Domain	Cell Type	Examples
Bacteria	Prokaryotic	Bacteria
Archaea	Prokaryotic	Methanogens, Halophiles, Thermophiles
Eukarya	Eukaryotic	Protists, Fungi, Plants, Animals, Algae

Phylogeny: The evolutionary relationships among organisms.

Diversity of Life

Bacteria

Bacteria are prokaryotes with peptidoglycan cell walls and reproduce by binary fission.

• Single chromosome

• No nucleus or membrane-bound organelles

• Energy from organic/inorganic chemicals or photosynthesis

Binary fission: Asexual reproduction where a cell divides into two identical cells.

Archaea

Archaea are prokaryotes lacking peptidoglycan, often found in extreme environments.

• Methanogens, extreme halophiles, extreme thermophiles

• Single chromosome

• No nucleus or membrane-bound organelles

Eukaryotes

Eukaryotes include animals, plants, fungi, protozoa, and algae. They have membrane-bound organelles and multiple chromosomes.

• Nucleus, mitochondria, chloroplasts, etc.

• Most are multicellular

Fungi

Fungi are eukaryotes with chitin cell walls, using organic chemicals for energy.

• Molds and mushrooms: Multicellular, composed of hyphae

• Yeasts: Unicellular

Algae

Algae are eukaryotes with cellulose cell walls, using photosynthesis for energy.

• Produce oxygen and organic compounds

• Rarely cause disease

Protozoa

Protozoa are eukaryotes that absorb or ingest organic chemicals and may be motile.

• Motility via pseudopods, cilia, or flagella

• Some are human parasites (e.g., malaria)

Multicellular Animal Parasites

These include multicellular eukaryotic animals such as flatworms and roundworms (helminths).

• Microscopic stages in life cycles

• Can be parasitic to humans

Viruses

Viruses are acellular entities consisting of DNA or RNA surrounded by a protein coat, sometimes with a lipid envelope.

• Replicate only inside living host cells

• Not classified as living organisms

History and Evolution of Microbiology

First Observations

• Ancestors of bacteria were the first life forms on Earth.

• First microbes observed in 1673.

• Robert Hooke (1665): Reported cells in cork.

• Anton van Leeuwenhoek (1673-1723): First to observe microbes.

• Rudolf Virchow: Proposed cell theory.

Spontaneous Generation vs. Biogenesis

• Spontaneous generation: Hypothesis that life arises from nonliving matter.

• Biogenesis: Hypothesis that life arises from preexisting life.

• Louis Pasteur (1861): Demonstrated microbes are present in the air, disproved spontaneous generation.

Condition	Result
Nutrient broth in flask, heated, sealed	No microbial growth
Nutrient broth in flask, heated, not sealed	Microbial growth

Pasteur's S-shaped flask allowed air in but kept microbes out, proving biogenesis.

Golden Age of Microbiology

• 1857-1914: Discoveries linking microbes to disease, immunity, and antimicrobial drugs.

Fermentation and Pasteurization

• Fermentation: Conversion of sugar to alcohol by microbes.

• Pasteurization: Application of high heat for a short time to kill spoilage bacteria.

Germ Theory of Disease

• Agostino Bassi (1835): Silkworm disease caused by fungus.

• Louis Pasteur (1865): Silkworm disease caused by protozoan.

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

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

• Robert Koch (1876): Proved specific microbes cause specific diseases (Koch's postulates).

Disease Therapy and Prevention

Vaccination

• Edward Jenner (1796): Developed smallpox vaccine using cowpox.

• Vaccination: Inoculation with a harmless variant to induce immunity.

Birth of Modern Chemotherapy

• Chemotherapy: Use of chemicals to treat disease.

• Antibiotics: Substances produced by microbes to inhibit other microbes.

• Quinine: Used to treat malaria.

• Sulfonamides: Synthetic antimicrobial agents.

• Alexander Fleming (1928): Discovered penicillin.

Microbes and Human Disease

Normal Microbiota

• Microbes normally present in and on the human body.

• Prevent growth of pathogens by occupying niches.

• Produce growth factors (e.g., folic acid, vitamin K).

Infectious Diseases

• Disease results when a pathogen overcomes host resistance.

• Emerging Infectious Diseases (EID): New or increasing diseases (e.g., HIV, Ebola, SARS, Lyme disease).

Modern Biotechnology and Genetic Engineering

Biotechnology uses microbes to produce foods and chemicals. Genetic engineering manipulates microbial genes for beneficial products.

• Production of proteins, vaccines, and enzymes

• Genetically modified organisms (GMOs) for agriculture