Microbiology: An Introduction, Chapter 1 - The Microbial World and You

Microbes in Our Lives

  • Learning Objectives:

    • 1-1 Ways microbes affect our lives:

    • Microbial Beneficial Actions:

      • Normal microbiota: Prevent growth of pathogenic microbes, train the immune system.

      • Photosynthetic microbes: Produce oxygen, are involved in food webs.

      • Food manufacturing: Fermentation processes in making bread, yogurt, cheese.

      • Industrial products: Production of chemicals like acetone.

    • Microbial Destructive Actions:

      • Pathogenic microbes: Cause diseases.

      • Food spoilage: Microorganisms can lead to spoilage of food products.

  • Definitions:

    • Microbiome: The community of microorganisms that live stably on or in the human body, contributing to health.

    • Normal Microbiota: The collection of microorganisms that reside indefinitely in a healthy human host.

    • Transient Microbiota: Microorganisms that are present temporarily for a short duration, often due to environmental exposure or antibiotic treatment.

  • Microorganisms: Organisms too small to be seen without a microscope such as:

    • Bacteria

    • Fungi

    • Protozoa

    • Microscopic algae

    • Viruses

    • Prions

Roles of Microbes

  • General Functions of Microorganisms:

    • Few are pathogenic and cause diseases.

    • Some contribute to food spoilage.

    • Essential components of food chains, especially in aquatic ecosystems.

    • Decompose organic waste, recycling nutrients back into the ecosystem.

    • Nitrogen fixation: Incorporate nitrogen gas from the atmosphere into organic compounds usable by plants.

    • Oxygen generation via photosynthesis.

    • Production of various chemicals (e.g., ethanol, vitamins) and fermented foods.

The Microbiome

  • Human Body Composition:

    • An adult human body contains approximately 30 trillion cells but also hosts around 40 trillion bacterial cells.

    • The microbiome plays key roles in maintaining health, preventing infections, and supporting immune function.

  • Acquisition of Microbiota:

    • Begins prior to birth and can persist indefinitely or temporarily (transient).

    • Only colonizes areas that provide adequate nutrients and environmental conditions for growth.

  • Human Microbiome Project (2007-2016): Aimed to identify the normal microbial communities in the human body and investigate their relationship with diseases.

  • National Microbiome Initiative (2016): Explores the roles of microbes in diverse ecosystems.

Naming and Classifying Microorganisms

  • Scientific Nomenclature:

    • Developed by Carolus Linnaeus in 1735.

    • Each organism has a two-part name: a genus (capitalized) and a specific epithet (lowercase).

    • Names are usually Latinized and universally recognized.

    • Examples include:

    • Homo sapiens (human)

    • Streptococcus pyogenes (bacterium).

  • Naming Conventions:

    • Scientific names are italicized or underlined. The first instance can use full names, following instances can abbreviate with initials (e.g., E. coli for Escherichia coli).

Types of Microorganisms

  • Major Groups:

    • Bacteria: Prokaryotic, unicellular, with peptidoglycan cell walls, reproduce by binary fission.

    • Archaea: Prokaryotic, lack peptidoglycan, often found in extreme environments, not typically pathogenic.

    • Fungi: Eukaryotic; cell walls made of chitin, can be unicellular (yeasts) or multicellular (molds, mushrooms).

    • Protozoa: Eukaryotic; motile, can be free-living or parasitic, reproduce sexually or asexually.

    • Algae: Eukaryotic; cellulose cell walls, photosynthetic, can be unicellular or multicellular.

    • Viruses: Acellular, consist of DNA or RNA surrounded by a protein coat, can only replicate inside host cells.

    • Multicellular Animal Parasites: Eukaryotic organisms that can exist in different life stages, may cause disease.

Classification of Microorganisms

  • The Three Domains:

    • Bacteria

    • Archaea

    • Eukarya (subdivided into protists, fungi, plants, and animals).

A Brief History of Microbiology

  • Key Historical Figures:

    • Robert Hooke (1665): Described cells, supporting the cell theory that all living things are made of cells.

    • Antoni van Leeuwenhoek (1673-1723): First observed microorganisms, calling them "animalcules".

  • Spontaneous Generation vs. Biogenesis:

    • Spontaneous Generation: Belief that life arises from nonliving matter.

    • Francesco Redi’s Experiment (1668): Showed that maggots on meat come from eggs, not spontaneously generated.

    • Needham’s Experiment (1745): Showed microbial growth in boiled broth placed in covered flasks leading to controversy.

    • Spallanzani’s Experiment (1765): Showed no growth in sealed boiled broth, challenging spontaneous generation.

    • Biogenesis: Concept that living cells arise only from pre-existing living cells, supported by Louis Pasteur’s work (1861).

  • Pasteur’s Contributions:

    • Developed pasteurization to kill spoilage bacteria in liquids.

    • Used S-shaped flasks to disprove spontaneous generation by allowing air flow while trapping microbes.

The Germ Theory of Disease

  • Key Discoveries:

    • Agostino Bassi (1835): Identified a fungus causing silk moth disease.

    • Joseph Lister (1860s): Introduced sterilization in surgery to prevent infections based on germ theory insights.

    • Robert Koch (1876): Developed Koch’s postulates to demonstrate that specific microbes cause specific diseases.

Vaccination**:

  • Edward Jenner’s work (1796) with cowpox helped establish immunity against smallpox, from which the term vaccination is derived.

The Second Golden Age of Microbiology

  • Focus on treatment of microbial diseases through chemistry and development of antibiotics.

    • Penicillin discovered by Alexander Fleming (1928), leading to its mass production to treat bacterial infections.

Emerging Topics in Microbiology

  • Molecular Genetics and Genomics

    • Microbial genetics studies how traits are inherited.

    • Genomics explores organisms' genetic material, facilitating advancements in microbial classifications and understanding environmental roles.

Applications of Microbes in Human Welfare

  • Beneficial Activities:

    • Recycling vital elements through the ecosystem.

    • Sewage Treatment: Using microbes to treat and recycle water.

    • Bioremediation: Microbes used to break down pollutants.

    • Insect Pest Control: Use of microbial insecticides as an eco-friendly alternative to chemical pesticides.

  • Biotechnology: Utilizes microbes for practical applications, including recombinant DNA technology to produce necessary proteins and enzymes, gene therapy, and genetically modified crops.

Microbes and Human Disease

  • Definitions:

    • Resistance: Ability to ward off disease, influenced by immunity and environmental factors.

    • Biofilm: Aggregates of microorganisms that can either be beneficial or harmful.

    • Emerging Infectious Diseases: New diseases that often arise from changes in ecology or microbial evolution.

  • Normal microbiota help provide immunity and produce nutrients for host health.