Welcome to Microbiology

Learning Outcomes

• Understand how microbes affect human life, both destructively and beneficially.

• Identify different branches in microbiology.

• Describe major characteristics of each group of microorganisms.

• Explain the three domains of microbial classification.

• Apply scientific naming conventions to microbes.

• Summarize the history of microbiology.

• Define biofilm and its importance.

• Define emerging infectious diseases and provide examples.

Types of Microorganisms

Overview

Microorganisms are classified based on cellular organization and include both cellular and acellular forms.

• Prokaryotes: Bacteria, Archaea

• Eukaryotes: Fungi, Protozoa, Algae

• Acellular: Viruses

Bacteria

• Prokaryotic, unicellular organisms.

• Exhibit several shapes (cocci, bacilli, spirilla, etc.).

• Cell walls contain peptidoglycan.

• Reproduce by binary fission.

• Obtain energy from organic chemicals, inorganic chemicals, or photosynthesis.

• Motility often via flagella.

• Example: Escherichia coli (E. coli)

Archaea

• Prokaryotic, lack peptidoglycan in cell walls.

• Live in extreme environments (e.g., high salt, temperature, or methane).

• Not known to cause disease in humans.

• Types include methanogens, extreme halophiles, and extreme thermophiles.

Fungi

• Eukaryotic; can be unicellular (yeasts) or multicellular (molds, mushrooms).

• Cell walls contain chitin.

• Use organic chemicals for energy.

• Multicellular fungi consist of masses of mycelia (composed of filaments called hyphae).

• Reproduce asexually and sexually.

Protozoa

• Eukaryotic, unicellular organisms.

• No cell walls.

• Absorb or ingest organic chemicals.

• Motile via pseudopods, cilia, or flagella.

• May be parasitic or free-living.

Algae

• Eukaryotic; unicellular or multicellular.

• Cell walls contain cellulose.

• Use photosynthesis for energy.

• Produce molecular oxygen and organic compounds.

• Reproduce sexually and asexually.

Viruses

• Acellular entities.

• Not considered living outside a host cell.

• Contain DNA or RNA as genetic material.

• Core is surrounded by a protein coat, sometimes enclosed in a lipid envelope.

• Replicate only inside living host cells.

• Very small; visible only with electron microscopy.

Classification of Microorganisms

Three Domains System

Microorganisms are classified into three domains based on cellular organization, a system developed by Carl Woese in 1978.

Nomenclature

Scientific Naming of Microbes

• Established by Linnaeus (1735).

• Each organism has two names: Genus and specific epithet (species name).

• Names are italicized or underlined; genus is capitalized, species is lowercase.

• Names are Latinized and used worldwide; may be descriptive or honor a scientist.

• Example: Escherichia coli honors Theodor Escherich and describes its habitat (colon).

• Example: Staphylococcus aureus describes clustered (staphylo-) spherical (coccus) cells and gold-colored (aureus) colonies.

Use of Scientific Names

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

• E. coli is found in the large intestine; S. aureus is found on skin.

History of Microbiology

The First Observations

• 1663–1665: Robert Hooke reported that living things are composed of cells, marking the beginning of cell theory.

• 1623–1673: Anton van Leeuwenhoek observed "animalicules" (microbes) through magnifying lenses.

The Debate over Spontaneous Generation

• Spontaneous generation: Hypothesis that life arises from nonliving matter; a "vital force" is necessary for life.

The Theory of Biogenesis

• Rudolf Virchow (1858): Proposed that cells arise from preexisting cells (biogenesis).

• Biogenesis: Living cells arise only from preexisting living cells.

Principles from Pasteur’s Work

• Microorganisms are present in air, liquids, and solids.

• Heat can destroy microorganisms.

• Methods can be designed to block airborne contamination.

• Developed principles for aseptic techniques to prevent microbial contamination.

The Golden Age of Microbiology (1857–1914)

• Pasteur’s work led to discoveries about the relationship between microbes and disease, immunity, and vaccines.

• Fermentation: Microbial conversion of sugar to alcohol in the absence of air.

• Microbial growth causes spoilage of food and beverages.

• Bacteria that use air spoil wine by turning it to vinegar (acetic acid).

• Pasteurization: Application of high heat for a short time to kill harmful bacteria in beverages.

The Germ Theory of Disease

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

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

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

• Joseph Lister: Introduced disinfectant for surgical wounds.

• Robert Koch (1876): Proved a bacterium causes anthrax; developed Koch’s postulates to link specific microbes to specific diseases.

Vaccination

• Edward Jenner (1796): Inoculated a person with cowpox virus, conferring immunity to smallpox.

• Immunity: Protection against disease.

The Birth of Modern Chemotherapy

• Chemotherapy: Treatment of disease with chemicals.

• Chemotherapeutic agents: Include antibiotics (naturally produced by bacteria/fungi) and synthetic drugs (chemically synthesized in the lab).

The First Synthetic Drugs

• Quinine: Used to treat malaria.

• Paul Ehrlich: Developed the concept of a "magic bullet" to destroy pathogens without harming the host.

• 1910: Developed salvarsan (synthetic arsenic drug) to treat syphilis.

• 1930s: Sulfonamides synthesized.

Antibiotics

• Alexander Fleming (1928): Discovered penicillin, the first antibiotic.

• 1940s: Penicillin tested clinically and mass-produced.

Microbes and Human Disease

Normal Microbiota

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

• Prevent growth of pathogens.

• Produce growth factors such as vitamins B and K.

Biofilms

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

• Grow on rocks, pipes, teeth, and medical implants.

• Biofilms can cause infections and are often resistant to antibiotics.

• Communicate through Quorum Sensing (QS).

Emerging Infectious Diseases (EIDs)

Definitions and Examples

• Infectious disease: Occurs when a pathogen invades a host and overcomes resistance.

• Resistance: Ability of the body to ward off disease (skin, mucous membranes, stomach acid, interferons).

• Emerging infectious diseases (EIDs): New diseases or those increasing in incidence.

Examples of EIDs

• Middle East Respiratory Syndrome Corona Virus (MERS-CoV): Same family as SARS; causes common cold; emerged as COVID-19 in 2020 (pandemic).

• Avian influenza A (H5N1): Bird flu; primarily in waterfowl and poultry; no sustained human-to-human transmission yet.

• Methicillin-Resistant Staphylococcus aureus (MRSA): Resistance to penicillin (1950s), methicillin (1980s), and vancomycin (1990s).

• E. coli O157:H7: Toxin-producing strain; causes bloody diarrhea; leading cause of diarrhea worldwide.

• Ebola hemorrhagic fever (EHF): Caused by Ebola virus; fever, hemorrhaging, blood clotting; transmitted via blood/body fluids.

• AIDS (acquired immunodeficiency syndrome): Caused by HIV; destroys CD4+ T cells; worldwide epidemic.

Summary Table

Additional info: These notes cover foundational concepts from Chapter 1: The Microbial World and You, including microbial classification, history, nomenclature, and the impact of microbes on human health and disease.