Chapter 1: The Microbial World and You – Study Notes

Chapter 1: The Microbial World and You

Introduction to Microbiology

Microbiology is the study of microorganisms, which are organisms too small to be seen with the unaided eye. This field encompasses a wide variety of life forms, including bacteria, fungi, protozoa, microscopic algae, and viruses. Understanding these organisms is essential for grasping their roles in health, disease, and the environment.

• Microorganisms: Organisms invisible to the naked eye.

• Include bacteria, fungi, protozoa, microscopic algae, and viruses.

• Some are pathogenic (disease-causing), while most are beneficial or neutral.

Roles of Microbes in Our Lives

Microbes play diverse roles in natural and human-made environments. Their activities are crucial for ecosystem functioning, industrial processes, and human health.

• Decompose organic waste, recycling nutrients.

• Generate oxygen via photosynthesis (e.g., algae).

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

• Ferment foods (vinegar, cheese, bread).

• Manufacture products (cellulose) and treat diseases (insulin).

• Knowledge of microbes helps prevent food spoilage, disease, and epidemics.

The Human Microbiome

The human body hosts trillions of microbial cells, collectively known as the microbiome. These microbes are essential for maintaining health and preventing disease.

• An adult human has ~30 trillion body cells and ~40 trillion bacterial cells.

• Microbiome: Stable community of microbes living on/in the human body.

• Functions: Maintains health, prevents pathogen growth, trains the immune system.

• Normal microbiota: Microbes acquired after birth, may be permanent or transient.

• Colonization depends on suitable nutrients and environment.

Major Projects:

• Human Microbiome Project (2007): Characterizes typical microbiota and their relation to disease.

• National Microbiome Initiative (2016): Explores microbial roles in ecosystems.

Naming and Classifying Microorganisms

Microorganisms are named and classified using a standardized system established by Carolus Linnaeus in 1735. Each organism has a two-part scientific name: genus and specific epithet.

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

• Names are Latinized and used worldwide.

• May be descriptive or honor a scientist.

Examples:

• Escherichia coli: Honors Theodor Escherich; found in the colon.

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

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

Types of Microorganisms

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

• Bacteria: Prokaryotic, single-celled, peptidoglycan cell walls, divide by binary fission, may be motile via flagella.

• Archaea: Prokaryotic, lack peptidoglycan, often live in extreme environments, include methanogens, halophiles, thermophiles, generally not pathogenic.

• Fungi: Eukaryotic, chitin cell walls, absorb organic chemicals, yeasts (unicellular), molds/mushrooms (multicellular, composed of hyphae).

• Protozoa: Eukaryotic, absorb/ingest organic chemicals, motile via pseudopods, cilia, or flagella, free-living or parasitic, some photosynthetic, reproduce sexually/asexually.

• Algae: Eukaryotic, cellulose cell walls, photosynthetic, found in water/soil, produce oxygen/carbohydrates, reproduce sexually/asexually.

• Viruses: Acellular, DNA or RNA core, protein coat (may have lipid envelope), replicate only in host cells, inert outside hosts.

• Multicellular Animal Parasites: Eukaryotic, multicellular, include helminths (flatworms, roundworms), some life stages are microscopic.

Type	Cell Type	Cell Wall	Reproduction	Motility	Example
Bacteria	Prokaryote	Peptidoglycan	Binary fission	Flagella	E. coli
Archaea	Prokaryote	No peptidoglycan	Binary fission	Varies	Methanogens
Fungi	Eukaryote	Chitin	Spores, budding	Non-motile	Yeast, mold
Protozoa	Eukaryote	None	Sexual/asexual	Pseudopods, cilia, flagella	Amoeba
Algae	Eukaryote	Cellulose	Sexual/asexual	Varies	Volvox
Viruses	Acellular	None	Host-dependent	None	Influenza virus
Helminths	Eukaryote	None	Sexual	Non-motile	Tapeworm

Classification of Microorganisms

Carl Woese (1978) developed a three-domain system based on cellular organization:

• Bacteria

• Archaea

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

Historical Foundations of Microbiology

Key discoveries laid the foundation for modern microbiology:

• 1665: Robert Hooke observed cells, beginning cell theory.

• 1623–1673: Anton van Leeuwenhoek observed microbes (“animalcules”).

Spontaneous Generation vs. Biogenesis

Early scientists debated the origin of life:

• Spontaneous generation: Life arises from nonliving matter; requires a "vital force".

• Biogenesis: Life arises only from preexisting life.

• Rudolf Virchow (1858): Cells arise from preexisting cells.

• Louis Pasteur disproved spontaneous generation using S-shaped flasks, showing microbes originate from air or fluids.

The Golden Age of Microbiology (1857–1914)

This era saw major advances in understanding microbes, disease, and immunity.

• Pasteur: Microbes cause fermentation and spoilage.

• Fermentation: Microbial conversion of sugar to alcohol without air.

• Bacteria spoil wine by converting alcohol to acetic acid.

• Pasteurization: High heat treatment to kill harmful bacteria in beverages.

The Germ Theory of Disease

The germ theory established that specific microbes cause specific diseases.

• 1835: Bassi (fungus causes silkworm disease).

• 1865: Pasteur (protozoan causes silkworm disease).

• 1840s: Semmelweis (handwashing prevents puerperal fever).

• 1860s: Lister (phenol prevents surgical infections).

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

Koch's Postulates: Experimental steps to prove a specific microbe causes a specific disease.

Summary Table: Koch's Postulates

Step	Description
1	Microbe must be found in all cases of the disease
2	Microbe must be isolated and grown in pure culture
3	Microbe must cause disease when introduced into a healthy host
4	Microbe must be re-isolated from the experimentally infected host

Additional info: These notes expand on the original slides by providing definitions, examples, and context for key microbiological concepts, including the historical development of the field and the classification of microorganisms.