The Microbial World and You

Definition and Importance of Microorganisms

Microorganisms, or microbes, are tiny living organisms that are usually too small to be seen with the naked eye. They play essential roles in the environment, human health, and industry.

• Germ: Derived from Latin, meaning "to sprout"; refers to microorganisms.

• Most microbes are beneficial rather than harmful.

• Microbes include bacteria, fungi (yeasts and molds), algae, some animals (parasitic worms), and non-living agents like viruses and prions.

• Bacteria are essential for health, acting as decomposers, nitrogen fixers, and producers of vitamins (e.g., B and K).

• Microbes are used in the production of antibiotics, drugs, and various foods (beer, wine, bread, cheese, yogurt).

Reasons to Study Microbiology:

• Essential to life and health

• Prevention and treatment of disease

• Career opportunities in health, research, and industry

Normal Flora and Human Health

• Normal flora (microbiota): Microorganisms that live on and inside the human body, providing protection and aiding in digestion and vitamin production.

• Humans have about 30 trillion human cells and approximately 40 trillion bacterial cells.

• Normal flora is acquired at birth and influenced by delivery method (vaginal vs. C-section), diet, and environment.

• The microbiota is well established by age 3 and remains stable until about age 65.

• Factors influencing microbiota: diet, genetics, environmental exposures.

History of Microbiology

Cell Theory

The cell theory is a fundamental concept in biology, stating:

• All living things are made of cells.

• The cell is the smallest unit of life.

• All cells arise from pre-existing cells.

Key Contributors:

• Robert Hooke and Antonie van Leeuwenhoek: Early discoveries using microscopes.

• Matthias Schleiden (1838): All plants are made of cells.

• Theodor Schwann (1839): All animals are made of cells.

• Rudolf Virchow: All living cells come from cell division of pre-existing cells.

The Golden Ages of Microbiology

• First Golden Age (1857–1914): Marked by Pasteur's work on microbes, disease, immunity, and antimicrobial drugs. Key questions included spontaneous generation, fermentation, disease causation, and disease prevention.

• Second Golden Age (1940–1980s): Focused on treatments, antibiotics, and synthetic drugs. Introduction of the "magic bullet" concept by Paul Ehrlich and the development of chemotherapy.

• Third Golden Age (1980s–Present): Ongoing advances in molecular biology, genetics, and biotechnology.

Key Discoveries and Theories

• Spontaneous Generation: The disproven idea that life can arise from non-living matter. Disproved by Louis Pasteur in 1858.

• Fermentation: Conversion of sugar to alcohol by yeast in the absence of oxygen (anaerobic respiration). Bacteria can spoil wine by converting alcohol to acetic acid (vinegar).

• Pasteurization: Heating liquids to kill microbes without altering taste.

• Germ Theory of Disease: The idea that microorganisms cause disease, replacing earlier beliefs in miasma (bad air) or supernatural causes.

• Koch's Postulates: Criteria to establish a causative relationship between a microbe and a disease.

Notable Scientists

• Louis Pasteur: Disproved spontaneous generation, developed pasteurization, and advanced the germ theory of disease.

• Robert Koch: Developed Koch's postulates, proved that specific bacteria cause specific diseases (e.g., anthrax).

• Ignaz Semmelweis: Introduced handwashing to prevent puerperal fever.

• Joseph Lister: Pioneered aseptic surgery using carbolic acid (phenol).

• Alexander Fleming: Discovered penicillin, the first antibiotic.

• Edward Jenner: Developed the smallpox vaccine.

Chemical Principles in Microbiology

Organic and Inorganic Compounds

• Organic compounds: Contain carbon-hydrogen bonds (e.g., carbohydrates, lipids, proteins, nucleic acids).

• Inorganic compounds: Usually lack carbon-hydrogen bonds (e.g., salts like NaCl, K2SO4, metals, CO2).

• CHNOPS: The six most important elements in biological molecules: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur.

Macromolecules

• Carbohydrates: Main energy source (sugars).

• Lipids: Fats, energy storage, and cell membrane structure.

• Proteins: Made of amino acids; function as enzymes and structural components.

• Nucleic Acids: DNA and RNA; store and transmit genetic information.

Observing Microorganisms Through a Microscope

Types of Microscopes

• Light Microscopy: Uses visible light to observe specimens.

• Compound Light Microscope: Uses multiple lenses (objective and ocular) to magnify images.

• Simple Microscope: Uses a single lens.

• Bright Field Microscopy: Light passes through specimen; objects appear dark against a bright background. Suitable for stained, fixed specimens.

• Dark Field Microscopy: Light is directed at an angle; objects appear bright against a dark background. Useful for live, unstained specimens.

• Phase Contrast Microscopy: Enhances contrast in unstained specimens; useful for observing living cells.

• Fluorescent Microscopy: Uses ultraviolet light and fluorescent dyes; highly specific and sensitive, often used for diagnostic purposes.

• Scanning Acoustic Microscopy: Uses sound waves to form images; useful for studying living cells attached to surfaces (e.g., biofilms).

• Electron Microscopy: Uses electron beams for high magnification and resolution; includes Scanning Electron Microscopy (SEM) for surface details and Transmission Electron Microscopy (TEM) for internal structures. Cannot be used on living specimens.

Staining Techniques

• Fixation: Kills and adheres cells to the slide.

• Simple Stain: Uses a single dye (e.g., crystal violet, methylene blue) to reveal cell morphology.

• Differential Stains: Distinguish between groups of bacteria.

  • Gram Stain: Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall structure.

  • Acid-Fast Stain: Identifies mycobacteria with waxy cell walls (e.g., Mycobacterium species).

• Special Stains: Used to visualize specific structures.

  • Capsule/Negative Stain: Stains background, leaving capsules as clear halos.

  • Endospore Stain: Identifies spore-forming bacteria.

  • Flagella Stain: Visualizes bacterial flagella.

  • Fluorescent Stain: Uses fluorescent dyes for specific labeling.

Prokaryotes vs. Eukaryotes

• All cells share three features: DNA, cytoplasm, and plasma membrane.

• Prokaryotes: Smaller, simpler, no nucleus, no membrane-bound organelles, divide by binary fission, cell wall contains peptidoglycan.

• Eukaryotes: Larger, more complex, have a nucleus and membrane-bound organelles, divide by mitosis, cell wall (if present) contains chitin or cellulose.

Microbial Metabolism

Overview of Metabolism

Metabolism is the sum of all chemical reactions within a living organism. It includes both catabolic (breakdown) and anabolic (synthesis) pathways.

• Catabolic reactions: Break down complex molecules, releasing energy (some stored as ATP, some lost as heat).

• Anabolic reactions: Use ATP to build larger molecules from smaller ones.

Energy Production from Glucose

• Microorganisms can produce energy from glucose via two main processes:

  1. Cellular Respiration (aerobic or anaerobic)

  2. Fermentation

• Some microbes can perform both processes; others are limited to one.

Aerobic Respiration

• Glycolysis: Oxidation of glucose to pyruvic acid, producing ATP and NADH.

• Krebs Cycle: Oxidation of acetyl-CoA, producing ATP, NADH, FADH2, and CO2.

• Electron Transport Chain (ETC): NADH and FADH2 are oxidized, generating large amounts of ATP as electrons are transferred to O2 (final electron acceptor).

Overall equation for aerobic respiration:

Fermentation

• Occurs in the absence of oxygen.

• Yields less ATP per glucose molecule compared to respiration.

• End products include ethanol and CO2 (yeast) or lactic acid (bacteria).

Example: Yeast fermentation of glucose to ethanol and CO2:

Additional info: The ATP yield from fermentation is typically 2 ATP per glucose, while aerobic respiration can yield up to 38 ATP per glucose in prokaryotes.