Introduction to Microbiology: Foundations, Diversity, and Impact

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: Common term for rapidly growing cells, often used to describe microbes, but a more precise term for disease-causing microbes is pathogen.

Microorganisms: Roles and Importance

• Decompose organic waste

• Producers in ecosystems via photosynthesis

• Produce industrial chemicals (e.g., ethanol, acetone)

• Ferment foods (e.g., vinegar, cheese, bread)

• Used in manufacturing and treatment (e.g., insulin)

• Most are harmless; a few are pathogenic (disease-causing)

Applications: Microbes are used in food production, biotechnology, and medicine. Only a small fraction cause disease.

Knowledge of Microorganisms

• Prevents disease occurrence

• Enables aseptic techniques in medicine and labs

Historical note: Techniques to prevent contamination and disease were developed as understanding of microbes grew.

Naming and Classifying Microorganisms

Scientific Naming

• Linnaeus established binomial nomenclature: each organism has a genus and species (e.g., Homo sapiens).

• Genus is capitalized and species is lowercase; both are italicized or underlined.

• Names may honor scientists or describe features (e.g., Staphylococcus aureus describes clustered cells and golden color).

• After first use, names may be abbreviated (e.g., S. aureus).

Note: Abbreviations can be confusing if multiple genera share the same initial.

Classification of Microorganisms

Three Domains of Life

• Bacteria (Prokaryotes)

• Archaea (Prokaryotes, distinct from bacteria)

• Eukarya (Eukaryotes: protists, fungi, plants, animals, algae)

Woes-Fox Classification System: Based on evolutionary relationships (phylogeny), showing the relatedness of all life forms.

Diversity of Life

Bacteria

• Prokaryotic, peptidoglycan cell walls

• Divide by binary fission

• Use organic/inorganic chemicals or photosynthesis for energy

• No nucleus or membrane-bound organelles

• Single circular chromosome

Peptidoglycan: Polymer of sugars and amino acids forming the cell wall.

Archaea

• Prokaryotic, lack peptidoglycan

• Live in extreme environments (e.g., methanogens, halophiles, thermophiles)

• No nucleus or membrane-bound organelles

• Single chromosome

Eukaryotes

• Include animals, plants, fungi, protozoa, algae

• Most are multicellular

• Multiple chromosomes

• Internal membrane-bound organelles (e.g., nucleus, mitochondria)

Fungi

• Eukaryotic, chitin cell walls

• Use organic chemicals for energy

• Molds/mushrooms: multicellular, composed of hyphae

• Yeasts: unicellular

Algae

• Eukaryotic, cellulose cell walls

• Photosynthetic, produce oxygen and carbohydrates

• Do not typically cause disease

Protozoa

• Eukaryotic, absorb/ingest organic chemicals

• Motile via pseudopods, cilia, or flagella

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

Multicellular Animal Parasites

• Eukaryotic, multicellular animals

• Parasitic flatworms and roundworms (helminths)

• Microscopic stages in life cycles

Viruses

• Acellular, consist of DNA or RNA core

• Core surrounded by protein coat, sometimes lipid envelope

• Replicate only in living host cells

• Not considered alive; not on the tree of life

History and Foundations of Microbiology

First Observations

• First microbes observed in 1673

• Robert Hooke (1665): Reported living things made of cells

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

• Rudolf Virchow (1858): Proposed all cells come from preexisting cells (Cell Theory)

Spontaneous Generation vs. Biogenesis

• Spontaneous generation: Life arises from nonliving matter

• Biogenesis: Life arises from preexisting life

• Louis Pasteur (1861): Demonstrated microbes are present in the air, disproved spontaneous generation with S-shaped flask experiment

Condition	Result
Broth heated, sealed	No microbial growth
Broth heated, not sealed	Microbial growth

Golden Age of Microbiology (1857-1914)

• Discoveries linking microbes to disease, immunity, and antimicrobial drugs

• Pasteur: Showed microbes responsible for fermentation and spoilage

• Pasteurization: Heating to kill spoilage bacteria

Germ Theory of Disease

• Microorganisms cause disease

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

• Pasteur (1865): Silkworm disease caused by protozoan

• Ignaz Semmelweis (1840s): Advocated handwashing to prevent transmission

• Joseph Lister (1860s): Used disinfectants in surgery

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

Vaccination and Chemotherapy

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

• Modern chemotherapy: Use of chemicals to treat disease (antibiotics, synthetic drugs)

• Alexander Fleming (1928): Discovered penicillin

Microbes and Human Health

Normal Microbiota

• Microbes normally present in/on the human body

• Prevent growth of pathogens (occupy niches, produce beneficial compounds)

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

Infectious Diseases

• Occur when pathogens overcome host resistance

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

Modern Biotechnology and Genetic Engineering

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

• Genetic engineering: Manipulation of microbial genes to produce proteins, vaccines, and genetically modified crops