Introduction to Microbiology

• Microbiology studies microorganisms, which are unicellular or exist as cell-cluster colonies
• Microorganisms consist of bacteria, archaea, fungi, protists, and viruses
• Sub-disciplines of microbiology are virology, mycology, parasitology, and bacteriology

Historical Context

• Antonie van Leeuwenhoek (1632-1723) discovered bacteria using his single-lens microscopes, and is known as the "father of microbiology"
• Louis Pasteur (1822-1895) developed pasteurization and contributed to germ theory
• Robert Koch (1843-1910) developed Koch's postulates, establishing criteria that links microorganisms to specific diseases

Cell Structure

• Prokaryotic cells (bacteria and archaea) do not have a nucleus or membrane-bound organelles
• Eukaryotic cells (fungi, protists) have a nucleus and other membrane-bound organelles
• Bacteria possess a peptidoglycan cell wall
• Gram-positive bacteria have a thick peptidoglycan layer which stains purple
• Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide (LPS), staining pink

Microbial Growth

• Microorganisms need nutrients, water, appropriate temperature and pH levels to grow
• Bacteria reproduce via binary fission
• Bacterial culture growth phases: lag, log (exponential), stationary, and death
• Aerobes need oxygen to grow
• Anaerobes don’t need oxygen, and can be killed by it
• Facultative anaerobes grow with or without oxygen

Microbial Metabolism

• Metabolism includes catabolism (complex molecules broken down) and anabolism (complex molecules synthesized)
• Bacteria use glycolysis, fermentation, and respiration for diverse metabolic pathways
• Fermentation, an anaerobic process, produces ATP and byproducts like lactic acid or ethanol
• Aerobic respiration uses oxygen as the final electron acceptor, while anaerobic uses other compounds

Microbial Genetics

• DNA is the genetic material in bacteria
• Plasmids are extrachromosomal DNA molecules, and carry genes for antibiotic resistance or other traits
• Bacteria transfer genetic material via transformation (DNA uptake from environment), transduction (transfer by bacteriophages), and conjugation (direct cell-to-cell contact)
• Mutations happen spontaneously or are induced by mutagens
• Recombination creates genetic diversity

Viruses

• Viruses are acellular infectious agents with nucleic acid (DNA or RNA) and a capsid (protein coat)
• Viruses replicate inside host cells, using the host's machinery
• Viral replication cycles: attachment, penetration, uncoating, replication, assembly, and release
• Viruses are classified based on nucleic acid type, capsid structure, and envelope presence
• Bacteriophages are viruses infecting bacteria

Microbial Ecology

• Microorganisms are essential in ecosystems for nutrient cycling and decomposition
• The human microbiome has diverse microbial communities colonizing the body
• Microbes are involved in biogeochemical cycles like nitrogen, carbon, and sulfur

Pathogenicity

• Pathogens are microorganisms that cause disease
• Virulence factors like toxins, adhesins, and enzymes contribute to pathogenicity
• Exotoxins, secreted by bacteria, can damage host cells
• Endotoxins, components of the bacterial cell wall (e.g., LPS), cause an immune response
• Host defenses: innate immune system (e.g., macrophages, complement) and adaptive immune system (e.g., antibodies, T cells)

Antimicrobial Agents

• Antibiotics either kill or inhibit bacterial growth
• Antibiotics target key bacterial processes like cell wall synthesis, protein synthesis, or DNA replication
• Antibiotic resistance develops through mutations or resistance gene acquisition
• Antiviral drugs target viral replication
• Antifungal drugs target fungal cell structures or metabolic pathways
• Sterilization eliminates all microorganisms
• Disinfection reduces microorganism numbers

Immunology

• Immunology studies the immune system
• The innate immune system provides immediate, non-specific defense
• The adaptive immune system gives specific, long-lasting immunity
• Antibodies (immunoglobulins) are produced by B cells which bind to specific antigens
• T cells mediate cellular immunity
• Vaccines stimulate the immune system for protective immunity

Diagnostic Microbiology

• Diagnostic microbiology identifies disease-causing microorganisms
• Methods encompass microscopy, culture, biochemical tests, and molecular techniques
• Gram staining differentiates bacteria
• Culture grows microorganisms in specific media
• Biochemical tests identify microorganism metabolic capabilities
• Molecular techniques like PCR detect microbial DNA or RNA

Industrial Microbiology

• Industrial microbiology uses microorganisms for commercial purposes
• Microorganisms are used in food, beverages, pharmaceuticals, and biofuels
• Fermentation creates ethanol, lactic acid, and antibiotics
• Bioremediation uses microorganisms to degrade pollutants

Food Microbiology

• Food microbiology studies microorganisms affecting food quality and safety
• Bacteria, fungi, or yeasts cause food spoilage
• Foodborne illnesses are caused by pathogenic microorganisms or their toxins
• Pasteurization, sterilization, and irradiation are employed to preserve food
• Fermented foods like yogurt, cheese, and sauerkraut are produced by microbial activity

Explore the fascinating world of microbiology, including microorganisms like bacteria, archaea, fungi, protists, and viruses. Learn about key historical figures such as Antonie van Leeuwenhoek, Louis Pasteur, and Robert Koch and their contributions. Understand the differences between prokaryotic and eukaryotic cells and bacterial cell structures.