Microbiology Fundamentals

Introduction to Microbiology

• Microbiology is the study of microscopic organisms including bacteria, viruses, fungi, protozoa, and algae.
• Microorganisms can be either beneficial or harmful to humans, animals, and the environment.

Key Figures in Microbiology

• Antonie van Leeuwenhoek (1670s) was the first to observe and describe microorganisms using a microscope and is known as the Father of Microbiology.
• Louis Pasteur (1800s) developed the germ theory of disease and created pasteurization and vaccines for rabies and anthrax.
• Robert Koch (1800s) formulated Koch’s postulates to prove that a specific microorganism causes a particular disease and identified the bacteria causing tuberculosis and cholera.
• Edward Jenner (1796) developed the first successful vaccine for smallpox.
• Alexander Fleming (1928) discovered penicillin, the first antibiotic.

Types of Microorganisms

• Bacteria are prokaryotic cells that can be beneficial, such as gut bacteria, or pathogenic, such as Escherichia coli and Streptococcus.
• Viruses are non-living particles made of genetic material and a protein coat that must infect a host cell to replicate; examples include the flu virus and HIV.
• Fungi are eukaryotic organisms that can be unicellular (yeasts) or multicellular (molds). Some are pathogenic like Candida, while others are used in food production.
• Protozoa are single-celled eukaryotes that can be free-living or parasitic; Plasmodium causes malaria.
• Algae are photosynthetic organisms often found in aquatic environments; some types are harmful.
• Helminths (worms) and arthropods (insects) are parasitic organisms that may cause disease, such as tapeworms and lice.

Microbial Classification

• Prokaryotes lack a nucleus and include bacteria.
• Eukaryotes have a nucleus and include fungi, protozoa, and algae.
• Viruses are not classified as living organisms.

Microbial Functions

• Beneficial microorganisms are involved in decomposition and nitrogen fixation.
• Beneficial microorganisms are used in food production for yeasts in baking and bacteria in fermentation for yogurt and cheese.
• Harmful microorganisms include pathogens, such as Staphylococcus aureus and HIV, that cause diseases.
• Infections result when pathogens invade and multiply in the body, evading immune defenses.

Microbial Techniques

• Staining is used to identify and classify bacteria; Gram stain differentiates Gram-positive and Gram-negative bacteria.
• Culturing involves growing microorganisms on nutrient media to identify and study them.

Microorganisms and Disease

• Diseases such as pneumonia, tuberculosis, influenza, and malaria are caused by microorganisms.
• The immune system protects the body against infections.
• Vaccines can prevent certain diseases by stimulating immune responses.

Bacterial Morphology (Shape and Structure)

• Cocci are spherical-shaped bacteria like Streptococcus and Staphylococcus.
• Bacilli are rod-shaped bacteria like Escherichia coli and Bacillus anthracis.
• Spirilla are spiral-shaped bacteria like Helicobacter pylori.
• Vibrio are comma-shaped bacteria like Vibrio cholerae.

Arrangement of Bacteria

• Diplo- refers to pairs, as seen in Neisseria gonorrhoeae.
• Strepto- refers to chains, as seen in Streptococcus species.
• Staphylo- refers to clusters, as seen in Staphylococcus aureus.
• Tetra- refers to groups of four, as seen in Micrococcus species.

Bacterial Structures

• Gram-positive bacteria have a thick peptidoglycan layer and retain crystal violet stain.
• Gram-negative bacteria have a thin peptidoglycan layer, an outer membrane, and retain safranin stain.
• The capsule is a slimy outer layer that protects bacteria from the host’s immune system and helps in adhesion.
• Flagella are long, whip-like structures that allow bacteria to move
• Flagella can be monotrichous, amphitrichous, peritrichous, or lophotrichous.
• Pili/Fimbriae are short hair-like projections used for attachment to surfaces and for genetic exchange (conjugation).
• Plasmids are small circular DNA molecules that carry extra genes and can transfer between bacteria.
• Endospores are protective structures formed by certain bacteria under harsh conditions.

Bacterial Physiology

• Aerobic bacteria require oxygen, like Mycobacterium tuberculosis.
• Anaerobic bacteria do not require oxygen, like Clostridium species.
• Facultative anaerobes can survive with or without oxygen, like Escherichia coli.
• Fermentation is how some bacteria produce energy without oxygen, like Lactobacillus in yogurt production.

Nutritional Requirements

• Heterotrophs rely on organic compounds or autotrophs use CO2 as a carbon source.
• A nitrogen source is essential for protein synthesis, and some bacteria fix nitrogen from the atmosphere.
• Vitamins and minerals are essential for various metabolic processes.

Bacterial Growth

• During the lag phase, bacteria adapt to a new environment with no significant growth.
• Log (Exponential) phase is when there is rapid division and growth.
• Stationary phase involves slowed growth due to nutrient depletion and accumulation of waste.
• Death phase is when bacteria begin to die due to a lack of nutrients and an accumulation of toxins.

Factors Affecting Bacterial Growth

• Bacteria have optimal growth temperatures.
• Mesophiles grow at human body temperature, 37°C.
• Most bacteria prefer a neutral pH of around 7, but some thrive in acidic or alkaline conditions.
• Different bacteria require different levels of oxygen: aerobic, anaerobic, or facultative.
• Moisture and osmotic pressure are essential for bacterial survival.
• Nutrient Agar is a common medium used to culture and grow bacteria in labs. It contains nutrients that support bacterial growth.

Bacterial Reproduction

• Binary fission is asexual reproduction where one bacterial cell divides into two identical cells.
• Conjugation is the exchange of genetic material between bacteria via pili.
• Transformation is the uptake of free DNA from the environment.
• Transduction is DNA transfer between bacteria via bacteriophages.

Types of Microbial Diseases

• Tuberculosis (TB) caused by Mycobacterium tuberculosis, affects the lungs.
• Pneumonia is inflammation of the lungs caused by bacteria like Streptococcus pneumoniae.
• Cholera, caused by Vibrio cholerae, leads to severe diarrhea and dehydration.
• Influenza is a viral infection affecting the respiratory system caused by the influenza virus.
• HIV/AIDS is caused by the Human Immunodeficiency Virus (HIV) that attacks the immune system.
• Hepatitis is inflammation of the liver caused by hepatitis viruses (A, B, C, D, E).
• Athlete’s Foot is caused by Trichophyton fungi and affects the skin.
• Candidiasis is caused by Candida species and leads to yeast infections.
• Malaria, caused by Plasmodium species, is transmitted by Anopheles mosquitoes.
• Giardiasis is caused by Giardia lamblia and leads to gastrointestinal issues.
• Toxoplasmosis is caused by Toxoplasma gondii and is transmitted through contaminated food or cat feces.

How Microbes Cause Disease

• Microbes attach to the surface of host cells using structures like pili and capsules (Adherence).
• Microbes penetrate host tissues, spreading infection via bloodstream or lymphatic system (Invasion).
• Some bacteria produce toxins, like Clostridium botulinum, that damage tissues or interfere with cellular processes (Toxin Production).
• Pathogens can evade the immune system with strategies like hiding inside cells, altering surface proteins, or producing chemicals that inhibit immune responses (Immune Evasion).

Immune System Overview

• The first line of defense is physical and chemical barriers and immune cells (Innate Immunity).
• Inflammation is a protective response to infection or injury (Innate Immunity).
• Adaptive immunity involves antibodies and T lymphocytes to target specific pathogens.
• B-cells produce antibodies that bind to pathogens and neutralize them (Adaptive Immunity).
• T-cells attack infected cells directly and help regulate immune responses (Adaptive Immunity).
• After an initial infection, the immune system "remembers" the pathogen, allowing for a faster and stronger response during future infections (Immunological Memory).

Types of Immunity

• Active immunity is acquired through exposure to a pathogen or vaccination.
• The body produces its own antibodies and memory cells with Active Immunity.
• Vaccines introduce harmless parts of a pathogen to stimulate an immune response without causing the disease, establishing Active Immunity.
• Passive immunity is gained through the transfer of antibodies from another individual.
• Herd immunity is when a large portion of a population is immune to a disease, providing protection to individuals who are not immune.

Vaccines and Immunization

• Vaccines prevent certain diseases by stimulating the adaptive immune system to recognize and respond to specific pathogens.
• Inactivated vaccines contain killed pathogens like the polio vaccine.
• Live attenuated vaccines contain weakened forms of pathogens like the MMR vaccine.
• Subunit vaccines contain only parts of the pathogen like the Hepatitis B vaccine.