Chapter 1: The Microbial World and You – Study Notes

The Microbial World and You

Introduction to Microbiology

Microbiology is the study of organisms too small to be seen with the unaided eye, known as microorganisms or microbes. These include bacteria, fungi, protozoa, microscopic algae, viruses, and prions. Microbes play essential roles in the environment, industry, and health, with only a minority being pathogenic.

Microbes in Our Lives

• Pathogenicity: A few microbes cause diseases in humans, animals, and plants.

• Food Spoilage: Some microbes are responsible for the spoilage of food and beverages.

• Ecological Roles: Microbes form the base of aquatic food chains, decompose organic waste, and recycle vital elements such as nitrogen and carbon.

• Industrial Applications: Microbes are used to produce chemicals (e.g., ethanol, acetone, vitamins), fermented foods (e.g., cheese, yogurt, bread), and pharmaceuticals (e.g., insulin).

The Microbiome

The microbiome refers to the community of microbes that live stably on and in the human body. An adult human harbors about 40 trillion bacterial cells, which help maintain health, prevent pathogen growth, and train the immune system.

• Normal microbiota: Microbes that are permanently present in or on the human body.

• Transient microbiota: Microbes that colonize the body for a short period.

• Colonization depends on suitable nutrients and environmental conditions.

Major Microbiome Projects

• The Human Microbiome Project (2007–2016): Mapped typical microbiota in various body regions and explored links to disease.

• The National Microbiome Initiative (2016–): Studies the role of microbes in diverse ecosystems.

Naming and Classifying Microorganisms

Scientific Nomenclature

Carolus Linnaeus established the binomial system of nomenclature in 1735. Each organism is given a two-part Latinized name: the genus (capitalized) and the specific epithet (lowercase). Names may be descriptive or honor scientists.

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

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

Classification of Microorganisms

Microorganisms are classified into three domains (Carl Woese, 1978):

• Bacteria

• Archaea

• Eukarya (includes protists, fungi, plants, and animals)

Types of Microorganisms

• Bacteria: Prokaryotic, unicellular, peptidoglycan cell walls, reproduce by binary fission, may have flagella.

• Archaea: Prokaryotic, lack peptidoglycan, often live in extreme environments, not known to cause disease.

• Fungi: Eukaryotic, chitin cell walls, absorb organic chemicals, include unicellular yeasts and multicellular molds/mushrooms.

• Protozoa: Eukaryotic, absorb/ingest organic chemicals, motile by pseudopods, cilia, or flagella, free-living or parasitic.

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

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

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

A Brief History of Microbiology

Early Observations

• 1665: Robert Hooke observed "cells" in cork, initiating cell theory.

• 1673–1723: Anton van Leeuwenhoek observed and described "animalcules" (bacteria, protozoa) using simple microscopes.

Spontaneous Generation vs. Biogenesis

• Spontaneous generation: Life arises from nonliving matter (disproven).

• Biogenesis: Life arises only from preexisting life (Rudolf Virchow, 1858).

• Louis Pasteur (1861): Demonstrated that microorganisms are present in the air and do not arise spontaneously using S-shaped flasks.

The Golden Ages of Microbiology

• First Golden Age (1857–1914): Discoveries included the relationship between microbes and disease, immunity, fermentation, pasteurization, aseptic techniques, and the first vaccines and chemotherapeutic drugs.

• Second Golden Age: Focused on chemotherapy and antibiotics (e.g., penicillin).

• Third Golden Age: Focused on genomics, molecular biology, and overcoming antimicrobial resistance.

Key Figures and Discoveries

• Joseph Lister: Introduced antiseptic surgery using phenol.

• Robert Koch: Developed Koch's postulates to link specific microbes to specific diseases.

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

• Paul Ehrlich: Developed the first synthetic drug (salvarsan) for syphilis.

• Alexander Fleming: Discovered penicillin, the first antibiotic.

Branches of Microbiology

• Bacteriology: Study of bacteria.

• Mycology: Study of fungi.

• Parasitology: Study of protozoa and parasitic worms.

• Immunology: Study of immunity; includes vaccines and interferons.

• Virology: Study of viruses.

Molecular Genetics and Genomics

• Microbial genetics: Study of inheritance in microbes.

• Molecular biology: Study of genetic information in DNA.

• Genomics: Study of an organism's genes; enables classification and understanding of microbiomes.

• Recombinant DNA: DNA from two sources; used for producing proteins and gene therapy.

Microbes and Human Welfare

Beneficial Activities of Microorganisms

• Recycling Elements: Bacteria convert elements (carbon, nitrogen, sulfur, phosphorus) into usable forms for plants and animals.

• Sewage Treatment: Microbes decompose organic matter in sewage, producing harmless by-products.

• Bioremediation: Microbes degrade pollutants such as oil and mercury.

• Insect Pest Control: Microbes like Bacillus thuringiensis are used as biological pesticides.

• Biotechnology: Use of microbes for producing foods, chemicals, and pharmaceuticals.

• Recombinant DNA Technology: Enables production of proteins, vaccines, and gene therapy.

Microbes and Human Disease

Normal Microbiota and Resistance

• Normal microbiota: Microbes that inhabit the human body and prevent pathogen growth.

• Resistance: The body's ability to ward off disease, involving skin, stomach acid, and immune chemicals.

Biofilms

Biofilms are complex microbial communities attached to surfaces. They can be beneficial (protecting mucous membranes, providing food in aquatic systems) or harmful (clogging pipes, causing infections, resisting antibiotics).

Emerging Infectious Diseases (EIDs)

EIDs are new or increasing diseases caused by pathogens overcoming host resistance. Factors include antibiotic resistance, global travel, and environmental changes.

• COVID-19: Caused by SARS-CoV-2, declared a pandemic in 2020.

• Mpox (Monkeypox): Orthopoxvirus, causes rash and flu-like symptoms.

• Zika Virus: Spread by mosquitoes, can cause birth defects.

• H1N1 Influenza (Swine Flu): Pandemic in 2009.

• Avian Influenza (H5N1): Bird flu, limited human transmission.

• Antibiotic-Resistant Infections: MRSA, VRSA, multidrug-resistant Mycobacterium tuberculosis, and Clostridium difficile.

• Ebola and Marburg Viruses: Cause hemorrhagic fevers with high mortality rates.