chap 1 micro

Introduction to Microbiology

What is Microbiology?

Microbiology is the study of microorganisms or microbes, which are organisms invisible to the naked eye. This field encompasses a wide variety of life forms, including bacteria, archaea, fungi, protozoa, and viruses, as well as prions (infectious proteins).

• Prokaryotic cells: Cells lacking a nucleus (e.g., bacteria, archaea).

• Eukaryotic cells: Cells with a nucleus (e.g., fungi, protozoa, algae, helminths).

• Viruses and prions: Non-cellular entities; viruses are infectious particles, prions are infectious proteins.

Pathogens are microbes that cause disease. Of the estimated 1,400 known human pathogens, less than 1% of all microbes are pathogenic. Some 'true' pathogens will always cause disease in humans, while opportunistic pathogens cause disease only in weakened hosts.

• Key Question: What is the difference between a pathogen, an opportunistic pathogen, and an obligate pathogen?

Relative Sizes of Microbes

Microbes vary greatly in size, from nanometers (viruses) to millimeters (some eukaryotes). The following table summarizes common units of measurement in microbiology:

Unit	Meaning of Prefix	Metric Equivalent
meter (m)	1	1 m = 1 m
decimeter (dm)	1/10	1 dm = 0.1 m = 10-1 m
centimeter (cm)	1/100	1 cm = 0.01 m = 10-2 m
millimeter (mm)	1/1,000	1 mm = 0.001 m = 10-3 m
micrometer (μm)	1/1,000,000	1 μm = 0.000001 m = 10-6 m
nanometer (nm)	1/1,000,000,000	1 nm = 0.000000001 m = 10-9 m

Living and Nonliving Agents Studied in Microbiology

Domain	Cell Type	Examples	Notes
Bacteria	Prokaryotic	Escherichia coli	Unicellular, diverse metabolism
Archaea	Prokaryotic	Halobacterium	Unicellular, often extremophiles
Fungi	Eukaryotic	Yeasts, molds	Unicellular or multicellular, decomposers
Protozoa	Eukaryotic	Amoeba	Unicellular, often motile
Algae	Eukaryotic	Chlamydomonas	Unicellular or multicellular, photosynthetic
Viruses	Non-cellular	Influenza virus	Obligate intracellular parasites
Prions	Non-cellular	PrPSc	Infectious proteins

A Brief History of Microbiology

Spontaneous Generation vs. Biogenesis

Early scientists debated whether life could arise spontaneously (spontaneous generation) or only from pre-existing life (biogenesis).

• Robert Hooke (mid-1600s): First to report descriptions of cells.

• Antonie van Leeuwenhoek (1673–1723): First to observe and describe bacteria using a simple microscope.

• Francesco Redi (1668–1670): Disproved spontaneous generation for larger organisms with his meat and maggot experiment.

• Louis Pasteur (1822–1895): Demonstrated that biogenesis is responsible for propagation of life. His swan-neck flask experiment disproved spontaneous generation for microbes.

Germ Theory of Disease

The germ theory of disease states that microbes cause infectious diseases.

• Robert Koch (1843–1910): Developed techniques to determine the specific etiological agent of diseases. His work with Bacillus anthracis and Mycobacterium tuberculosis was foundational.

• Koch's Postulates: A series of criteria used to establish a causative relationship between a microbe and a disease.

1. The same organism must be present in every case of the disease.

2. The organism must be isolated and grown as a pure culture.

3. The isolated organism should cause the disease when introduced into a susceptible host.

4. The organism must be re-isolated from the inoculated, diseased animal.

Note: Not all microbes can be cultured, and not all diseases fit these postulates.

Hand Hygiene and Aseptic Techniques

From the 1800s to the 1900s, medical advances highlighted the importance of aseptic techniques in preventing healthcare-associated infections (HAIs).

• Ignaz Semmelweis: Advocated handwashing to prevent puerperal fever.

• Joseph Lister: Introduced sterilization of instruments and use of antiseptics.

• Florence Nightingale: Promoted hygiene in nursing and hospital settings.

Aseptic techniques include:

• Washing hands

• Wearing gloves

• Sterilizing instruments

• Decontaminating surfaces

Sterile means absent of all microbes.

The Scientific Method in Microbiology

The scientific method is the guiding principle for investigations in microbiology.

1. Formulate a hypothesis (a testable explanation).

2. Collect and analyze observations (data).

3. Draw conclusions based on data.

4. Develop theories or laws based on repeated, consistent results.

• Law: A precise statement or mathematical formula that predicts a specific occurrence.

• Theory: A hypothesis that has been proven through many studies with consistent, supporting conclusions.

• Observation: Any data collected using senses or instrumentation.

• Conclusion: Interpretation of observations.

Classifying Microbes and Their Interactions

Taxonomy and Classification

Taxonomy is the science of classifying organisms based on shared features. The modern system is hierarchical:

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

The six-kingdom classification system includes:

Kingdom	Examples
Bacteria	Prokaryotes
Archaea	Prokaryotes, extremophiles
Protista	Protozoa, algae
Fungi	Yeasts, molds
Plantae	Plants
Animalia	Animals, helminths

Binomial nomenclature assigns each organism a two-part scientific name: Genus (capitalized) and species (lowercase), both italicized (e.g., Escherichia coli).

Microbial Relationships and the Human Microbiome

• Symbiosis: Close ecological relationship between two species.

• Parasitism: One organism benefits at the expense of the other (e.g., pathogens).

• Mutualism: Both organisms benefit.

• Commensalism: One benefits, the other is unaffected.

Normal microbiota (normal flora) are microbes that colonize the human body without causing disease. They help train the immune system, produce vitamins, and aid digestion.

• Disruption of normal microbiota (e.g., by antibiotics) can lead to disease.

• Transient microbiota: Temporary microbes acquired from the environment, removed by hygiene.

Biofilms

Biofilms are sticky communities of microbes that adhere to surfaces and are embedded in a protective matrix. They are medically significant because they are difficult to eradicate and can cause persistent infections.

• Biofilms form on teeth (dental plaque), catheters, and water pipes.

• Cells in biofilms communicate and share nutrients.

• Biofilms are resistant to antibiotics and immune responses.

Environmental and Industrial Uses for Microbes

Bioremediation is the use of microbes to clean up pollutants and toxic wastes. Certain bacteria can metabolize oil spills or degrade hazardous substances into harmless products.

• Hundreds of microbial species can degrade petroleum oil spills to CO2.

Host–Microbe Interactions and Human Evolution

Close relationships with microbes have influenced human evolution. For example, malaria (caused by a protozoan) has led to the persistence of the sickle cell gene in certain populations, as carriers are less likely to develop severe malaria.

Summary Table: Key Concepts in Microbiology

Concept	Definition/Example
Microbiology	Study of microorganisms
Pathogen	Microbe that causes disease
Normal microbiota	Microbes that colonize the body without causing disease
Biofilm	Community of microbes attached to a surface
Bioremediation	Use of microbes to clean up pollutants
Symbiosis	Close relationship between two organisms
Binomial nomenclature	Two-part scientific naming system

Additional info: The notes above expand on the original slides by providing definitions, examples, and context for key microbiology concepts, as well as summarizing important tables and figures for clarity and completeness.