Microbiology: The Microbial World and You - Chapter 1 Study Notes

The Microbial World and You

Microbes in Our Lives

Microorganisms, or microbes, are organisms too small to be seen with the unaided eye. They play essential roles in both beneficial and harmful processes affecting human life and the environment.

• Definition: Microorganisms include bacteria, fungi, protozoa, microscopic algae, and viruses.

• Destructive Actions: Some microbes are pathogenic (disease-producing).

• Beneficial Actions:

  • Decompose organic waste

  • Generate oxygen via photosynthesis

  • Produce chemical products (e.g., ethanol, acetone, vitamins)

  • Produce fermented foods (e.g., vinegar, cheese, bread)

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

• Applications: Knowledge of microbes helps prevent food spoilage, prevent disease, and understand disease transmission to prevent epidemics.

The Microbiome

The microbiome refers to the community of microbes living stably on or in the human body. These microbes are crucial for maintaining health and preventing disease.

• Normal microbiota: The collection of acquired microorganisms on or in a healthy human being.

• Transient microbiota: Microbes that colonize the body fleetingly.

• Colonization: Occurs only at body sites providing nutrients and suitable environments.

• Functions:

  • Prevent growth of pathogenic microbes

  • Help train the immune system to discriminate threats

• Human Microbiome Project: Begun in 2007 to determine the makeup of typical microbiota and their relationship to disease.

• National Microbiome Initiative: Begun in 2016 to explore the role of microbes in ecosystems.

Naming and Classifying Microorganisms

Microorganisms are named and classified using a standardized system established by Carolus Linnaeus in 1735.

• Scientific Nomenclature: Each organism has two names: genus (capitalized) and specific epithet (lowercase), both italicized or underlined.

• Examples:

  • Escherichia coli: Honors Theodor Escherich; habitat is the colon.

  • Staphylococcus aureus: Describes clustered spherical cells and gold-colored colonies.

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

Types of Microorganisms

Microorganisms are classified into several major groups based on cellular structure and function.

• Bacteria: Prokaryotes, single-celled, peptidoglycan cell walls, divide by binary fission, may use flagella for movement.

• Archaea: Prokaryotes, lack peptidoglycan, often live in extreme environments, include methanogens, extreme halophiles, and thermophiles.

• Fungi: Eukaryotes, chitin cell walls, absorb organic chemicals, yeasts (unicellular), molds and mushrooms (multicellular).

• Protozoa: Eukaryotes, absorb or ingest organic chemicals, motile via pseudopods, cilia, or flagella, free-living or parasitic.

• Algae: Eukaryotes, cellulose cell walls, photosynthetic, produce oxygen and carbohydrates.

• Viruses: Acellular, DNA or RNA core, protein coat, replicate only in living host cells.

• Multicellular Animal Parasites: Eukaryotes, multicellular animals, include helminths (flatworms and roundworms).

Classification of Microorganisms

Carl Woese developed a classification system based on cellular organization, dividing life into three domains.

• Bacteria

• Archaea

• Eukarya: Includes protists, fungi, plants, and animals.

A Brief History of Microbiology

The First Observations

Early observations laid the foundation for cell theory and microbiology.

• Robert Hooke (1665): Reported that living things are composed of cells.

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

The Debate Over Spontaneous Generation

Spontaneous generation was the hypothesis that life arises from nonliving matter, while biogenesis posited that living cells arise only from preexisting cells.

• Francesco Redi (1668): Experimented with decaying meat to test spontaneous generation.

• John Needham (1745): Boiled nutrient broth in covered flasks.

• Lazzaro Spallanzani (1765): Boiled nutrient solutions in sealed flasks.

• Rudolf Virchow (1858): Proposed biogenesis.

• Louis Pasteur (1861): Demonstrated that microorganisms are present in the air and disproved spontaneous generation using S-shaped flasks.

The Golden Age of Microbiology

From 1857 to 1914, major discoveries established the relationship between microbes, disease, immunity, and antimicrobial drugs.

• Pasteur: Demonstrated fermentation and pasteurization.

• Germ Theory of Disease:

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

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

  • Ignaz Semmelweis (1840s): Advocated handwashing.

  • Joseph Lister (1860s): Used antiseptics in surgery.

  • Robert Koch (1876): Discovered anthrax bacterium; developed Koch's postulates.

• Vaccination: Edward Jenner (1796) inoculated with cowpox for smallpox immunity.

The Birth of Modern Chemotherapy

Chemotherapy involves treating disease with chemicals, including synthetic drugs and antibiotics.

• Quinine: Used to treat malaria.

• Paul Ehrlich (1910): Developed salvarsan for syphilis.

• Sulfonamides (1930s): Synthetic drugs.

• Alexander Fleming (1928): Discovered penicillin.

• Problems: Overuse leads to resistance; some drugs are toxic.

Modern Developments in Microbiology

Bacteriology, Mycology, Parasitology, Immunology, and Virology

Microbiology encompasses several specialized fields.

• Bacteriology: Study of bacteria.

• Mycology: Study of fungi.

• Parasitology: Study of protozoa and parasitic worms.

• Immunology: Study of immunity; vaccines and interferons are used to prevent and cure viral diseases.

• Virology: Study of viruses.

Molecular Genetics and Genomics

Advances in genetics and molecular biology have revolutionized microbiology.

• Microbial genetics: Study of how microbes inherit traits.

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

• Genomics: Study of an organism’s genes; provides tools for classifying microorganisms.

• Recombinant DNA: DNA made from two different sources.

Microbes and Human Welfare

Recycling Vital Elements

Microbial ecology studies the relationship between microorganisms and their environment. Microbes recycle elements such as carbon, oxygen, nitrogen, sulfur, and phosphorus.

Sewage Treatment and Bioremediation

• Sewage Treatment: Microbes convert organic materials in sewage into by-products like carbon dioxide.

• Bioremediation: Bacteria degrade or detoxify pollutants such as oil and mercury.

Insect Pest Control by Microorganisms

• Bacillus thuringiensis: Produces protein crystals toxic to insects; used as an alternative to chemical pesticides.

Biotechnology and Recombinant DNA Technology

• Biotechnology: Use of microbes for practical applications (e.g., producing foods and chemicals).

• Recombinant DNA technology: Enables production of proteins, vaccines, and enzymes; used in gene therapy and crop protection.

Microbes and Human Disease

Normal Microbiota and Resistance

• Normal microbiota: Microbes normally present in and on the human body; prevent growth of pathogens and produce growth factors (e.g., vitamins B and K).

• Resistance: Ability of the body to ward off disease; factors include skin, stomach acid, and antimicrobial chemicals.

Biofilms

Microbes attach to solid surfaces and grow into masses called biofilms, which can cause infections and are often resistant to antibiotics.

Emerging Infectious Diseases

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

• Examples:

  • Zika virus disease

  • Middle East respiratory syndrome (MERS)

  • H1N1 influenza (swine flu)

  • Avian influenza A (H5N1)

  • Methicillin-resistant Staphylococcus aureus (MRSA)

  • Ebola hemorrhagic fever

  • Marburg virus

Key Terms and Concepts

• Microbiome: Community of microbes living on/in the human body

• Normal microbiota: Acquired microorganisms in healthy humans

• Transient microbiota: Temporary colonizers

• Genus and specific epithet: Scientific naming system

• Prokaryotes: Cells without a nucleus (bacteria, archaea)

• Eukaryotes: Cells with a nucleus (fungi, protozoa, algae, parasites)

• Biogenesis: Life arises from preexisting life

• Spontaneous generation: Life arises from nonliving matter (disproved)

• Pasteurization: High heat treatment to kill harmful bacteria

• Germ theory of disease: Microbes cause disease

• Koch's postulates: Steps to link a microbe to a disease

• Antibiotics: Chemicals produced by microbes to inhibit or kill other microbes

• Biofilm: Microbial community attached to surfaces

• Emerging infectious diseases: New or increasing diseases

Table: Classification of Microorganisms

Group	Cell Type	Cell Wall	Reproduction	Nutrition
Bacteria	Prokaryote	Peptidoglycan	Binary fission	Organic/inorganic/photosynthesis
Archaea	Prokaryote	No peptidoglycan	Binary fission	Organic/inorganic
Fungi	Eukaryote	Chitin	Sexual/asexual	Absorption
Protozoa	Eukaryote	No cell wall	Sexual/asexual	Absorption/ingestion
Algae	Eukaryote	Cellulose	Sexual/asexual	Photosynthesis
Viruses	Acellular	None	Host cell replication	Host cell
Multicellular Animal Parasites	Eukaryote	None	Complex life cycle	Host

Example: Koch's Postulates

• The same pathogen must be present in every case of the disease.

• The pathogen must be isolated from the diseased host and grown in pure culture.

• The pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.

• The pathogen must be re-isolated from the inoculated animal and shown to be the original organism.

Example: Pasteur's S-shaped Flask Experiment

• Broth boiled in S-shaped flask remained free of microbes.

• Neck of flask trapped airborne microbes, preventing contamination.

• Demonstrated that microbes originate from air, not spontaneous generation.

Relevant Images

Summary

This study guide covers the foundational concepts of microbiology, including the types and classification of microorganisms, the history of microbiology, the role of microbes in health and disease, and modern applications in biotechnology and genetics. Understanding these principles is essential for further study in microbiology and related fields.