Microbiology and Immunology

• Microbiology is the study of microorganisms, including bacteria, archaea, fungi, protists, and viruses
• Immunology is the study of the immune system, which protects the body from pathogens and other harmful substances

Branches of Microbiology

• Bacteriology studies bacteria.
• Mycology studies fungi.
• Protozoology studies protozoa.
• Virology studies viruses.
• Parasitology studies parasites.
• Microbial Ecology explores interactions between microbes and their environment.
• Microbial Genetics studies the genetics of microorganisms.
• Medical Microbiology studies the role of microbes in human disease.

Characteristics of Microorganisms

• Microorganisms are ubiquitous and found in almost all environments.
• They can be unicellular or multicellular organisms.
• They use diverse metabolic strategies.
• Many microorganisms benefit the environment through essential roles in nutrient cycling, decomposition, and food production.
• Some microorganisms are pathogenic, causing disease in humans, animals, and plants

Bacterial Structure

• Bacteria are prokaryotic cells, lacking a nucleus and other membrane-bound organelles.
• Basic bacterial structures include a cell wall, cell membrane, cytoplasm, nucleoid, and ribosomes.
• The cell wall provides shape and rigidity, protecting against osmotic lysis.
• The cell membrane encloses the cytoplasm, regulating substance passage.
• The cytoplasm contains water, enzymes, nutrients, and genetic material.
• The nucleoid contains a single, circular DNA molecule as the bacterial chromosome.
• Ribosomes are involved in protein synthesis.
• Some bacteria have a capsule, flagella, pili (fimbriae), and plasmids.
• The capsule, a polysaccharide layer outside the cell wall, provides protection and aids in attachment.
• Flagella are whip-like appendages used for motility.
• Pili (fimbriae) are hair-like appendages used for surface attachment.
• Plasmids are small, circular DNA molecules carrying non-essential genes

Viral Structure

• Viruses are non-cellular entities with nucleic acid (DNA or RNA) and a capsid.
• Nucleic acid carries genetic information.
• The capsid, a protein coat, protects the nucleic acid.
• Some viruses have an envelope and spikes.
• The envelope is a lipid bilayer from the host cell membrane.
• Spikes are glycoprotein projections that aid host cell attachment.

Microbial Growth

• Microbial growth is the increase in cell number, not individual cell size.
• Bacteria reproduce via binary fission, where one cell divides into two identical daughter cells.
• Factors affecting microbial growth include temperature, pH, oxygen, nutrients and water availability.
• The bacterial growth curve includes the lag, log (exponential), stationary, and death (decline) phases.
• During the lag phase, bacteria adapt to the new environment with little cell division.
• The log (exponential) phase involves rapid cell division and population doubling at a constant rate.
• The stationary phase sees growth rate equal to death rate because of nutrient depletion and waste accumulation.
• In the death (decline) phase, the death rate exceeds the growth rate, leading to population decline.

Microbial Metabolism

• Microorganisms use diverse metabolic strategies for energy and nutrients.
• Key metabolic processes include aerobic respiration, anaerobic respiration, fermentation, and photosynthesis.
• Aerobic respiration requires oxygen as the final electron acceptor to produce ATP.
• Anaerobic respiration uses molecules like sulfate or nitrate as the final electron acceptor.
• Fermentation is an anaerobic process that produces ATP from organic compound breakdown.
• Photosynthesis uses light energy to convert carbon dioxide and water to organic compounds.

Microbial Genetics

• Bacteria possess a single circular chromosome containing all essential genes.
• Plasmids are small, circular DNA molecules with non-essential genes.
• Genetic variation in bacteria happens through mutation and horizontal gene transfer.
• Mutation involves changes in the DNA sequence.
• Horizontal gene transfer involves genetic material transfer between bacteria including transformation, transduction, and conjugation.
• Transformation is the uptake of naked DNA from the environment.
• Transduction is the transfer of DNA by a virus.
• Conjugation is the transfer of DNA through direct cell-to-cell contact.

Control of Microbial Growth

• Methods to control microbial growth include sterilization, disinfection, and antisepsis.
• Sterilization eliminates all microorganisms and can be achieved via autoclaving, filtration, and radiation.
• Autoclaving uses high-pressure steam.
• Filtration removes microorganisms using filters.
• Radiation uses UV or ionizing radiation.
• Disinfection reduces the number of pathogenic microorganisms using chemical disinfectants or heat.
• Chemical disinfectants kill or inhibit microbial growth.
• Heat is used via boiling or pasteurization.
• Antisepsis disinfects living tissue using antiseptics.
• Antiseptics are chemical agents applied to the skin or mucous membranes.

Introduction to the Immune System

• The immune system defends the body against pathogens and harmful substances.
• It consists of innate and adaptive immunity.
• Innate immunity provides immediate, non-specific protection.
• Adaptive immunity develops over time, providing specific, long-lasting protection.

Innate Immunity

• Components of the innate immune system include physical, chemical, and cellular defenses, inflammatory response, and the complement system.
• Physical barriers include skin and mucous membranes.
• Chemical barriers include lysozyme and stomach acid.
• Cellular defenses include phagocytes and natural killer (NK) cells.
• Phagocytes engulf and destroy pathogens; examples include macrophages and neutrophils.
• Natural Killer (NK) Cells kill infected or cancerous cells.
• The inflammatory response is localized, characterized by redness, swelling, heat, and pain.
• The complement system enhances antibodies and phagocytic cells to clear microbes and damaged cells, promotes inflammation, and attacks pathogen membranes.

Adaptive Immunity

• Specificity and memory characterize the adaptive immune system.
• Specificity is the ability to recognize and respond to specific antigens.
• Memory allows a faster, stronger response upon re-exposure to an antigen.
• B cells and T cells are components of the adaptive immune system.
• B cells produce antibodies, which neutralize pathogens or mark them for destruction.
• T cells include helper T cells and cytotoxic T cells.
• Helper T cells coordinate the immune response by activating other immune cells.
• Cytotoxic T cells kill infected or cancerous cells.
• Humoral and cell-mediated immunity are types of adaptive immunity.
• Humoral immunity is mediated by antibodies produced by B cells.
• Cell-mediated immunity is mediated by T cells.

Antigens

• Antigens elicit an immune response and can be proteins, polysaccharides, lipids, or nucleic acids.
• Epitopes are the specific antigen regions recognized by antibodies or T cell receptors.

Antibodies (Immunoglobulins)

• Antibodies are proteins produced by B cells that bind to specific antigens.
• Classes of antibodies include IgG, IgM, IgA, IgE, and IgD.
• IgG is the most abundant antibody in serum and provides long-term immunity.
• IgM is the first antibody produced during an infection.
• IgA is in mucosal secretions and protects against pathogens entering through mucosal surfaces.
• IgE is involved in allergic reactions and parasitic infections.
• IgD is found on the surface of B cells and plays a role in B cell activation.

Immunological Disorders

• Immunodeficiency disorders result from a weakened or absent immune system and can be primary (genetic defects) or secondary (acquired due to infections, malnutrition, or immunosuppressive drugs).
• Primary immunodeficiency results from genetic defects.
• Secondary immunodeficiency results from infections (e.g., HIV), malnutrition, or immunosuppressive drugs.
• Autoimmune disorders involve the immune system attacking the body's own tissues.
• Hypersensitivity reactions are exaggerated immune responses to harmless antigens.
• Type I hypersensitivity involves immediate allergic reactions mediated by IgE.
• Type II hypersensitivity involves antibody-mediated cell destruction (cytotoxic).
• Type III hypersensitivity involves deposition of antibody-antigen complexes in tissues.
• Type IV hypersensitivity involves T cell-mediated delayed reactions.