Medical Microbiology Introduction

Introduction and Origin

• Microbes are living organisms needing a microscope to be seen, ranging from 0.2 µm to 5 mm in size.
• There are an estimated 10^12 microbial species, with only a small fraction identified.
• Microbes include bacteria, archaea, and eukarya.
• Fred Sanger developed the first method for DNA sequencing fast enough to sequence large genomes.

Impact of Microbes on Human History

• Major epidemics (e.g., Plague of Justinian, Black Death, Spanish flu) have killed millions, shaped history.
• HIV/AIDS and COVID-19 significantly impacted global health and well-being.
• Florence Nightingale recognized the importance of disease in warfare.
• She developed the scientific method of microbiology, proving the link between microbes and disease.
• She founded the principles of medical statistics and professional nursing.

Origins of Medical Microbiology

• Robert Koch established the scientific method for microbiology, linking microbes to specific diseases.
• He proved the germ theory of disease, showing how microbes cause infections.
• He used anthrax to demonstrate the chain of infection.
• Koch's postulates are used to establish the disease causation link between microbes and infections.

Microbial Ecology and Environment

• Lithotrophs used inorganic materials for their energy.
• Sergei Winogradsky developed enrichment cultures.
• Extremophiles are organisms living in extreme environments.
• Endosymbionts are microbes living symbiotically inside a larger organism.
• Biofilms are slimy layers formed by microbes sticking together in communities.

Cell Biology and the Amazing DNA Revolution

• Frederick Griffith discovered bacterial transformation.
• Oswald Avery discovered DNA was the transforming substance, proving its role in heredity.

Discovery and Observation

• Resolution limits the smallest distance objects can be distinguished
• The human eye can only distinguish about 150 microns
• Microbes vary significantly in size, covering several orders of magnitude.

Optics and Properties of Light

• Electromagnetic radiation is composed of perpendicular electric and magnetic waves.
• Visible light has a wavelength range of 400-750 nm.
• Refraction changes light's direction entering a substance with a higher refractive index.
• Magnification uses the bending of light (refraction) increasing the apparent size of objects.
• Parabolic lenses concentrate or spread light based on the specific shapes.

Cell Biology and Microscopy

• Eukaryotic and prokaryotic microbes have various sizes in the range of micrometers (µm) to nanometers (nm).
• Light microscopy, scanning and transmission electron microscopes, and other advanced techniques are used for observing and studying microorganisms.
• Staining techniques can enhance cell visualization using various dyes and stains.
• Wet mounts are simple preparation methods, while fixation and staining techniques enhance contrast.
• Fluorescence microscopy uses fluorescent materials for detailed studies, allowing specific visualization of cells and structures within them.

Electron Microscopy

• Electron microscopy uses electrons instead of light for high magnification.
• Transmission electron microscopy (TEM) involves the passing of electrons through a specimen.
• Scanning electron microscopy (SEM) involves scanning the surface of a specimen with electrons.

Structure and Function

• The bacterial cell comprises cytoplasm, a cell membrane, and commonly a cell wall
• Cell fractionation separates subcellular components.
• Ultracentrifuges separate particles based on size and density.
• Cell membrane is a semi-permeable phospholipid bi-layer, which controls entry and exit of molecules.
• Unsaturated fatty acids increase membrane fluidity, while saturated ones decrease it.
• Hopanoids stabilize or modify membrane fluidity in various environments.
• Membrane molecules participate in active and passive transport across the membrane.

Genomes and Replication

• The genome represents the complete set of genetic material within a cell.
• DNA consists of a double helix where bases are paired in specific combinations: G with C and A with T.
• Organisms possess a variety of supercoiling for DNA packaging.
• Circular DNA differs from linear DNA in its structure and organization.
• DNA polymerase III is a key enzyme used during replication.
• DNA replication uses one parental strand to synthesize a new complementary strand.
• Replication proceeds in two opposite directions around the chromosome.
• Plasmids are extrachromosomal DNA molecules that replicate independently.

Additional Topics

• Bacterial cell walls differ structurally between Gram-positive and Gram-negative bacteria.
• Bacterial cell walls are made of peptidoglycans, and unique structures contribute to their functions (e.g, virulence and resistance).
• Different types of microscopy are used for observing a variety of microorganisms like bacteria, fungi, algae, and viruses.
• Various microscopy techniques exist, each offering unique capabilities to improve resolutions and visual analyses.
• Eukaryotic microbes have unique internal structures like vacuoles to deal with osmotic stress.
• Prokaryotic microbes like bacteria reproduce via binary fission, resulting in two identical daughter cells.
• DNA replication is semi-conservative (synthesizes a new strand using a template)-
• Processes like transformation, transduction, and conjugation. Discuss how genetic material can be transferred between different bacterial cells in various scenarios.