Chapter 1 – The Microbial World and You: Study Notes

Chapter 1 – The Microbial World and You

Destructive and Beneficial Actions of Microbes

Microorganisms play crucial roles in both harming and benefiting humans and the environment.

• Destructive actions: Cause infectious diseases, food spoilage, and bio-deterioration.

• Beneficial actions: Decompose organic matter, recycle nutrients, produce antibiotics, and aid in food production (e.g., yogurt, cheese).

• Example: Lactobacillus in yogurt production; Streptococcus pyogenes causing strep throat.

Scientific Nomenclature

The system of scientific nomenclature assigns each organism a two-part name: the genus and the specific epithet (species).

• Format: Genus is capitalized, species is lowercase, both italicized (e.g., Escherichia coli).

• Purpose: Provides universal identification and classification.

Prokaryotes vs. Eukaryotes

Microbes are classified as either prokaryotes or eukaryotes based on cellular structure.

• Prokaryotes: Lack a true nucleus and membrane-bound organelles (e.g., bacteria, archaea).

• Eukaryotes: Have a true nucleus and membrane-bound organelles (e.g., fungi, protozoa, algae).

Phototrophs and Cellular Respiration

Microorganisms can be classified by their energy and carbon sources.

• Phototrophs: Obtain energy from light.

• Cellular respiration: Process by which cells convert nutrients into energy (ATP), often using oxygen.

• Classification: Autotrophs (self-feeding) vs. heterotrophs (require organic compounds).

Domains and Kingdoms

All life is classified into three domains and further into kingdoms.

• Three domains: Bacteria, Archaea, Eukarya.

• Four kingdoms in Eukarya: Protista, Fungi, Plantae, Animalia.

Contributions of Hooke and van Leeuwenhoek

Early scientists made significant discoveries in microbiology.

• Robert Hooke: First to observe "cells" in cork; contributed to cell theory.

• Antonie van Leeuwenhoek: First to observe living microorganisms using a simple microscope.

Cell Theory

The cell theory states that all living things are composed of cells, and cells are the basic unit of life.

Spontaneous Generation vs. Biogenesis

Debate over the origin of life led to important experiments.

• Spontaneous generation: Life arises from nonliving matter.

• Biogenesis: Life arises only from pre-existing life.

• Example: Pasteur's swan-neck flask experiment disproved spontaneous generation.

Germ Theory of Disease

The germ theory states that microorganisms are the cause of many diseases.

• Key contributors: Pasteur, Koch.

• Significance: Led to development of aseptic techniques and modern medicine.

Koch’s Postulates

Koch’s postulates are criteria to establish a causative relationship between a microbe and a disease.

• Microbe must be found in all cases of the disease.

• Microbe must be isolated and grown in pure culture.

• Pure culture must cause disease in a healthy host.

• Microbe must be re-isolated from the experimentally infected host.

Vaccination and Immunity

Vaccination stimulates the immune system to develop protection against specific pathogens.

• Edward Jenner: Developed the first vaccine (smallpox).

• Immunity: The ability to resist infection by pathogens.

Magic Bullet and Chemotherapy

Paul Ehrlich proposed the concept of a "magic bullet"—a chemical that targets pathogens without harming the host.

• Magic bullet: Led to the development of antimicrobial drugs (e.g., Salvarsan for syphilis).

• Chemotherapy: Use of chemicals to treat disease.

Subfields of Microbiology

Microbiology includes several specialized fields:

• Bacteriology: Study of bacteria.

• Virology: Study of viruses.

• Mycology: Study of fungi.

• Parasitology: Study of parasites.

• Immunology: Study of the immune system.

• Etiology: Study of the cause of disease.

Infectious Disease and Medical Microbiology

Medical microbiology focuses on the diagnosis, treatment, and prevention of infectious diseases.

• Pathogen: A microorganism that causes disease.

• Infectious disease: Disease caused by pathogenic microorganisms.

Microbial Evolution

Microbes have evolved diverse metabolic and structural adaptations.

• Mutation: Source of genetic variation.

• Natural selection: Favors beneficial traits.

Microbial Structures

Microorganisms possess unique structures that contribute to their survival and pathogenicity.

• Cell wall: Provides shape and protection (e.g., peptidoglycan in bacteria).

• Flagella: Enable motility.

• Pili and fimbriae: Aid in attachment and conjugation.

Viruses and Prions

Viruses are acellular infectious agents; prions are infectious proteins.

• Viruses: Consist of genetic material (DNA or RNA) surrounded by a protein coat.

• Prions: Misfolded proteins that cause neurodegenerative diseases.

Emergence of Infectious Diseases

New infectious diseases can emerge due to microbial evolution, environmental changes, and human activity.

• Factors: Mutation, antibiotic resistance, global travel, climate change.

Prokaryotic Cell Structure

Prokaryotic cells have a simple structure compared to eukaryotes.

• Key features: Cell wall, plasma membrane, cytoplasm, ribosomes, nucleoid (no true nucleus).

• Absent: Membrane-bound organelles.