Foundations and Key Figures in Microbiology: Concepts, Microbial Diversity, and Techniques

Robert Hooke

First to observe eukaryotic cells using a microscope, leading to the formulation of the cell theory, which states that all living organisms are composed of cells.

Antoni van Leeuwenhoek

The first to observe living microorganisms through magnifying lenses, which he called 'animalcules,' in rainwater, feces, and material scraped from teeth.

Carl Linnaeus

Developed the binomial nomenclature system for naming organisms, which is still in use today for classifying living things.

Edward Jenner

Pioneered vaccination by using cowpox to confer immunity against smallpox, laying the foundation for immunology.

Louis Pasteur

Developed the Germ Theory. Disproved spontaneous generation and established biogenesis. He showed that microbes are responsible for fermentation and spoilage and developed pasteurization.

Joseph Lister

Introduced antiseptic surgical techniques, significantly reducing post-operative infections. His work laid the foundation for modern surgical practices. He emphasized the use of carbolic acid to sterilize surgical instruments and clean wounds, which greatly improved patient outcomes.

Robert Koch

Confirmed the germ theory of disease by proving that Bacillus anthracis causes anthrax in cattle. Published Koch's Postulates, a framework for linking specific pathogens to specific diseases. He developed methods for isolating and culturing bacteria, contributing to microbiology as a discipline.

What are Koch's Postulates?

1. Pathogen found in every diseased host

2. Isolate pathogen in pure culture

3. Healthy host develops disease after inoculation

4. Reisolate the same pathogen

Christian Gram

Developed the Gram stain procedure in 1884, a differential staining technique that classifies bacteria into Gram-positive and Gram-negative groups.

Alexander Fleming

Discovered penicillin, the first true antibiotic, which revolutionized medicine and the treatment of bacterial infections.

Carl Woese

Developed the three-domain system of classification (Bacteria, Archaea, and Eukarya) based on sequences of ribosomal RNA (16S rRNA).

Who is Antonie van Leeuwenhoek?

Observed living bacteria for the first time, providing evidence of microbial life and expanding the understanding of the microscopic world.

Microbiology

The study of organisms too small to be seen with the naked eye.

Microbes (Microorganisms)

Living things that are generally too small to be seen without a microscope; includes bacteria, fungi, protozoa, microscopic algae, and viruses.

Unicellular

Organisms composed of a single cell (e.g., bacteria, most protozoa).

Multicellular

Organisms composed of many cells (e.g., animals, plants, most fungi).

Prokaryote

A cell whose genetic material is not enclosed in a nuclear envelope; lacks membrane-bound organelles. Domains Bacteria and Archaea, Smaller (1–10 μm)

Eukaryote

A cell having DNA inside a distinct nucleus and containing membrane-bound organelles. Can be unicellular or multicellular. Includes plants, animals, fungi, algae, and protozoa. Larger (10-100 μm)

Bacteriology

The study of bacteria.

Mycology

The study of fungi.

Taxonomy

The science of classifying organisms; provides universal names for organisms.

Hierarchy of Organisms

Life is organized into a nested hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Bacteria

Prokaryotes; cell walls contain peptidoglycan. Example: Staphylococcus aureus.

Archaea

Prokaryotes; cell walls lack peptidoglycan; often live in extreme environments. Example: Methanobacterium.

Eukarya

Eukaryotes; include Kingdoms Protista, Fungi, Plantae, and Animalia. Example: Homo sapiens.

Binomial Nomenclature

Scientific names are italicized or underlined. The Genus is capitalized; the specific epithet (species) is lowercase.

Total Magnification

Calculated by multiplying the objective lens power by the ocular lens power.

Phase-Contrast Microscopy

Permits detailed examination of internal structures in living microorganisms without staining.

Darkfield

Uses a special condenser so that only light reflected off the specimen enters the objective; specimen appears light against a dark background; ideal for live, unstained specimens.

Fluorescence

Uses UV light source; specimens are stained with fluorochromes; appears as bright objects against dark background.

Electron Microscopy

Uses electrons instead of light; much higher resolution due to shorter wavelength.

Transmission Electron Microscope (TEM)

Electrons pass through ultra-thin sections; used to see internal cell structures; magnification $10,000 imes$ to $1,000,000 imes$.

Scanning Electron Microscope (SEM)

Electrons scan the surface of a whole specimen; provides 3D views of the surface; magnification $1,000 imes$ to $500,000 imes$ .

Eukaryotes

Algae, Protozoa, and Fungi.

Heterotrophic

Uses organic compounds as a carbon source.

Photoautotrophic

Uses light energy and $CO_2$ as a carbon source.

Binary Fission

Simple division into two.

Budding

Outgrowth of a parent cell forms a new cell.

Conjugation

Genetic exchange between two cells.

Algae

Photoautotrophic eukaryotes; mostly aquatic.

Green Algae

Spirogyra (filamentous), Volvox (colonial), Scenedesmus.

Brown Algae

Used for algin (thickener).

Red Algae

Used for agar and carrageenan.

Diatoms vs. Dinoflagellates

Diatoms have pectin and silica cell walls and store energy as oil. Dinoflagellates are plankton that can produce neurotoxins (Red Tide).

Trophozoite

The vegetative, feeding, and growing stage.

Cyst

A protective capsule that allows survival in adverse conditions.

Amoebozoa

Move by pseudopods (e.g., Entamoeba histolytica).

Euglenozoa

Move by flagella (e.g., Trypanosoma - sleeping sickness).

Ciliophora

Move by cilia (e.g., Paramecium).

Apicomplexa

Non-motile in mature forms; obligate intracellular parasites. Illnesses include Malaria (Plasmodium), Toxoplasmosis (Toxoplasma), and Cryptosporidiosis (Cryptosporidium).

Hyphae

Filaments of cells; can be septate (with cross-walls) or aseptate/coenocytic (no cross-walls).

Mycelium

A mass of hyphae.

Conidiospores

Asexual spores not enclosed in a sac.

Sporangiospores

Asexual spores enclosed in a sac.

Zygospores

Sexual spores of Zygomycota.

Ascospores

Sexual spores of Ascomycota.

Basidiospores

Sexual spores of Basidiomycota.

Yeast

Unicellular fungi; fission yeasts divide symmetrically, while budding yeasts divide asymmetrically.

Virus

Obligate intracellular parasite containing either DNA or RNA.

Virion

A complete, fully developed, infectious viral particle.

Pandemic

A worldwide epidemic.

Nucleic Acid

DNA or RNA, single or double-stranded.

Capsid

Protein coat protecting the nucleic acid.

Capsomere

Protein subunits that make up the capsid.

Envelope

Lipid, protein, and carbohydrate coating over the capsid (found in some viruses).

Prions

Proteinaceous infectious particles; cause spongiform encephalopathies (e.g., Mad Cow disease).

Atom Structure

Nucleus contains protons (positive charge) and neutrons (no charge). Electrons (negative charge) orbit the nucleus.

Element

A substance that cannot be broken down into simpler substances. (e.g., Carbon (C), Hydrogen (H), Oxygen (O)).

Molecules and Compounds

Molecules are two or more atoms held together. Compounds contain at least two different elements ($H_2O$).

Ionic Bond

Formed by the attraction between cations (positive ions) and anions (negative ions).

Covalent Bond

Formed when atoms share electrons. Can be polar (unequal sharing) or nonpolar (equal sharing).

Hydrogen Bond

A weak bond formed when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom.

Synthesis Reaction

$A + B \rightarrow AB$: Anabolism.

Decomposition Reaction

$AB \rightarrow A + B$: Catabolism.

Exchange Reaction

$AB + CD \rightarrow AD + CB$: Part synthesis, part decomposition.

Carbohydrates

Function as energy sources. Composed of C, H, and O in a $2:1$ ratio of H to O.

Lipids

Consist of C, H, and O but lack the $2:1$ H:O ratio. Insoluble in water.

Proteins

Building blocks are amino acids. Joined by peptide bonds.

Denaturation

Loss of shape and function due to temperature or pH changes.

Nucleic Acids

Building blocks are nucleotides (pentose sugar, phosphate group, nitrogenous base). Examples: DNA, RNA, ATP.

Coccus

Spherical shape of prokaryotic cells.

Bacillus

Rod-shaped prokaryotic cells.

Strepto-

Arrangement of prokaryotic cells in chains.

Staphylo-

Arrangement of prokaryotic cells in clusters.

Diplo-

Arrangement of prokaryotic cells in pairs.

Flagella

Used for motility in prokaryotic cells.

Monotrichous

Single flagellum arrangement.

Amphitrichous

Flagella at both ends of the cell.

Peritrichous

Flagella all over the prokaryotic cell.

Taxis

Movement toward or away from a stimulus.

Chemotaxis

Movement in response to chemical stimuli.

Phototaxis

Movement in response to light stimuli.

Fimbriae

Hair-like appendages used for attachment.

Pili

Involved in DNA transfer (conjugation) and motility.

Gram-Positive

Thick peptidoglycan layer; contains teichoic acids.

Gram-Negative

Thin peptidoglycan layer; contains lipopolysaccharide (LPS).

Osmosis

Movement of water across a selectively permeable membrane.

Isotonic

No net movement of water.

Hypotonic

Water moves into the cell, potentially causing lysis.

Hypertonic

Water moves out of the cell, causing plasmolysis.