Chapter 1 Study Guide: The Microbial World and You
Chapter 1: The Microbial World and You
Overall Theme
The course focuses on the relationship between microbes, which are very small organisms, and human lives.
Disease Definitions
Epidemic: A rapid spread of disease to a large number of hosts in a given population within a short period of time.
Defined by: An attack rate of over 15 cases per 100,000 people for two consecutive weeks.
Meningitis: An infection/inflammation of the meninges, the membranes enveloping the brain and spinal cord.
Meningococcal meningitis: Bacterial meningitis caused by Neisseria meningitidis.
Pandemic: The worldwide spread of a new disease.
Commonly associated with viral respiratory diseases, such as those caused by new influenza viruses or coronaviruses like COVID-19.
Distinction: A pandemic differs from an epidemic in its global scope.
Historical Context: Cholera Outbreak
Broad Street cholera outbreak (1854): Severe choleral outbreak in Soho, London, during the 1846-1860 worldwide cholera pandemic.
Microbial Classification
Staphylococcus aureus:
Staphylococcus aureus is a Gram-positive, spherically shaped bacterium, commonly found in the upper respiratory tract and skin.
It is a facultative anaerobe, meaning it can grow without oxygen.
While it usually acts as a commensal microbe, it can become opportunistic, causing skin infections, respiratory infections, and food poisoning.
Early Observations in Microbiology
Robert Hooke (1665):
Observed a thin slice of cork and described the smallest structural units as "little boxes" (cells).
This discovery laid the groundwork for Cell Theory, which states that all living things are composed of cells.
Anton van Leeuwenhoek (1673-1723):
A Dutch merchant and amateur scientist, first to observe live microorganisms (termed "animalcules") through magnifying lenses.
Created detailed drawings and is referred to as the „Father of Microbiology”.
Theory of Biogenesis
Biogenesis vs. Spontaneous Generation:
Prior to the 19th century, it was largely believed that life could arise from non-living matter (spontaneous generation).
Rudolf Virchow (1858): Proposed biogenesis, which posits that living cells arise only from pre-existing living cells.
Louis Pasteur (1861): Disproved spontaneous generation by demonstrating that microorganisms in the air contaminate sterile solutions without air creating microbes.
Pasteur's Experiment:
Infusion boiled to kill microorganisms.
After a few days, no microorganisms appeared in the infusion until the flask was tipped, allowing trapped microorganisms to enter.
Resulted in microbial growth, contributing to aseptic technique formation.
Significant Figures in Microbiology
Joseph Lister (1827-1912):
Conducted surgery under aseptic conditions using phenol, proving that microbes caused surgical wound infections.
Robert Koch (1843-1910):
Established experimental steps linking specific microbes to specific diseases through Koch's Postulates:
The microorganism must be found in abundance in all diseased organisms, not in healthy ones.
It must be isolated from a diseased organism and grown in pure culture.
Cultured microorganism should cause disease when introduced into a healthy organism.
It must be re-isolated from the inoculated, diseased host and identified as identical to the original organism.
Advances in Microbiology
First Golden Age of Microbiology
Pasteurization: A process of heating liquids to high temperatures for short times to kill harmful microbes without affecting taste or nutritional value.
Germ Theory of Disease: States that diseases are caused by microorganisms, which are too small to see without a microscope.
Vaccines: Biological agents eliciting an immune response to specific antigens from pathogens, providing immunity.
Second Golden Age of Microbiology
First Synthetic Drugs:
Paul Ehrlich (1909): Synthesized arsphenamine (Salvarsan), the first synthetic drug against syphilis.
Sulfonamide: Noted by Gerhard Domagk in the 1900s for its antibacterial properties, particularly prontosil as an anti-bacterial dye.
Penicillin: Discovered by Alexander Fleming in 1928; identified the active agent from the Penicillium mold with antibacterial effects on staphylococci and other gram-positive pathogens.
Third Golden Age of Microbiology
Genomics: The study of DNA and its functions within organisms, including gene interaction and functionality.
Recombinant DNA Technology: Involves manipulating DNA segments for splicing between species or creating new gene functions.
Microbes in Our Lives
Germ Definition: Originates from the Latin german, meaning to sprout. Used in the 19th century for rapidly growing cells causing disease.
Microorganisms: Minute living entities, generally invisible to the naked eye, including bacteria, fungi (yeasts and molds), protozoa, and microscopic algae.
Ecological Importance:
Marine and freshwater microorganisms form the basis of food chains.
Soil microbes decompose waste and recycle nutrients (e.g., nitrogen fixation).
Certain microbes are essential for photosynthesis.
Human Microbiome
An adult human has approximately 30 trillion body cells alongside another 40 trillion bacterial cells.
These microbes constitute the human microbiome or microbiota, crucial for maintaining health.
Gut bacteria (e.g., E. coli) help in digestion and vitamin synthesis, with microbial colonization starting before birth.
Microbial Classification
Binomial Nomenclature: Assigns two names to organisms: the genus (capitalized) and specific epithet (lowercase).
Example: Staphylococcus aureus refers to clustered spherical organisms, where aureus means golden.
Example: Escherichia coli named after Theodor Escherich, indicating its habitat in the colon.
Types of Microorganisms: Important for health care and treatment of infections, including bacteria, archaea, fungi, protozoa, algae, viruses, and multicellular animal parasites.
The Three Domains of Life
Bacteria:
Cell walls composed of peptidoglycan.
Archaea:
Lack peptidoglycan in their cell walls (if present).
Eukarya:
Includes Protists, Fungi, Plants, and Animals.
Bacterial Characteristics
Prokaryotes: Simple, single-celled organisms.
Shapes:
Bacillus: Rodlike.
Coccus: Spherical.
Spiral: Corkscrew or curved.
Bacteria reproduce via binary fission (asexual reproduction).
Some are motile via flagella.
Archaea Characteristics
Prokaryotes that often thrive in extremophilic conditions.
Methanogens: Methane-producing.
Extreme Halophiles: Live in highly saline environments.
Extreme Thermophiles: Found in very hot sulfurous waters.
Generally not pathogenic to humans.
Fungi Characteristics
Eukaryotes: Have a nucleus containing DNA.
Unicellular (yeasts) or multicellular (molds, mushrooms).
Cell walls primarily composed of chitin.
Nourishment derives from the environment.
Microbes and Human Welfare
Microbes play a vital role in various processes:
Production of alternative fuels: Methane and ethanol.
Recycling of vital elements: Carbon, nitrogen, oxygen, sulfur, and phosphorus.
Water Recycling: Using microbes for sewage treatment via decomposition of organic matter.
Insect Pest Control: Using bacterial toxins in lieu of chemical pesticides.
Bioremediation: Employing microbes to detoxify pollutants (toxic waste, oil spills).
Applications in Biotechnology
Biotech advancements through recombinant DNA have expanded the utilization of microbes.
Applications include the production of proteins, vaccines, enzymes, and synthetic substances like human insulin.
Microbes and Human Disease
Microbes are part of a healthy human flora but can cause disease when they invade susceptible hosts.
Our immune system fights pathogens with white blood cells, the inflammatory response, and fever.
Biofilms: Microbial communities that can be helpful or harmful.
Example: Biofilms protect mucous membranes but can clog water pipes and cause infections on medical devices.
Antibiotic resistance can be increased in biofilms due to protective barriers.
Infectious Diseases
Defined as diseases where pathogens invade and often reproduce in a host, resulting in typical disease symptoms.
Emerging Infectious Diseases (EIDs)
EIDs indicate that infectious diseases are not disappearing but re-emerging or increasing due to:
Evolutionary changes in organisms.
Spread of known diseases to new populations via modern transport.
Increased human exposure to new infectious agents due to ecological changes (deforestation, construction).