Intro to Micro and Epidemiology

Introduction to Microbiology and its Scope

• Definition: Microbiology is the specific branch of science dedicated to the study of microorganisms. These are organisms that are typically too small to be seen clearly without a microscope.

• Core Organisms Studied:

  • Bacteria

  • Viruses

  • Fungi

  • Protozoa

• Ecosystem and Biological Importance: Microorganisms are vital to the planetary web of life, participating in:

  • Nutrient cycling.

  • Decomposition of organic matter.

  • Human health maintenance.

• Major Sub-disciplines:

  • Medical Microbiology: Centered on microbes that cause disease and the development of treatments for those diseases.

  • Environmental Microbiology: Focused on the ecological roles of microbes within natural habitats.

  • Industrial Microbiology: Involves the use of microbes in manufacturing processes, production, and biotechnology.

• Applications: Understanding these organisms leads to advancements in human health, agricultural productivity, and environmental sustainability.

The Historical Foundations of Microbiology

• Early History:

  • Ancient civilizations utilized microbial processes like fermentation to produce beer and bread.

  • Concept of Contagion: Ancient people recognized disease transmission, leading to the isolation of individuals in leper colonies and the development of sanitation systems like aqueducts and sewers.

  • Hippocrates: A Greek physician who challenged mystical explanations for disease, proposing that illnesses had natural, identifiable causes.

• Antoni van Leeuwenhoek ($1632$-$1723$):

  • Known as a "Father of Microbiology."

  • Professionally a Dutch cloth merchant who developed high-quality lenses to inspect fabric quality.

  • He was the first to observe and document microscopic life, which he called "wee beasties" and "animalcules."

The Golden Age of Microbiology ($1857$-$1914$)

This era was characterized by a rapid acceleration in the discovery and understanding of the microbial world.

• Spontaneous Generation vs. Biogenesis:

  • Spontaneous Generation: The belief that life arises spontaneously from non-living matter when conditions are favorable (e.g., mice appearing in a cornfield because food is present).

  • Biogenesis: The principle that living things arise only from pre-existing living things (e.g., mice are born from parent mice).

• Francesco Redi's Experiments:

  • Open container: Maggots formed in the meat.

  • Cork-sealed container: No maggots formed.

  • Gauze-covered container: No maggots formed in the meat, proving that maggots come from flies, not the meat itself.

• Needham vs. Spallanzani:

  • John Needham: Heated broth and left the flask open; growth occurred, which he used to support spontaneous generation.

  • Lazzaro Spallanzani: Heated broth and sealed the flask; no growth occurred. Critics argued he had simply cut off the "vital force" (air) necessary for life.

• Louis Pasteur's Swan-Necked Flask Experiment:

  • Pasteur definitively settled the debate by using a flask with an S-shaped neck (swan neck).

  • Scenario $1$: Pure broth was heated and cooled; the S-neck trapped airborne microbes, and the broth remained pure indefinitely.

  • Scenario $2$: If the flask was tilted so the broth touched the microbes trapped in the neck, the broth became contaminated.

  • Scenario $3$: If the neck was broken, allowing microbes direct access, the broth became contaminated within hours or days.

• Contributions of Louis Pasteur:

  • Settled the biogenesis debate.

  • Established the foundations for the Scientific Method.

  • Saved the French wine industry through his work on fermentation.

  • Developed Plusieurs vaccines, notably for rabies.

• The Scientific Method:

  1. Make an Observation.

  2. Ask a question.

  3. Formulate a Hypothesis (a statement attempting to answer the question).

  4. Experimentation (testing the hypothesis).

  5. Analyze data and draw conclusions.

  6. Share findings.

Robert Koch and the Foundations of Etiology

• Robert Koch: Another "Father of Microbiology" who focused on the causative agents of specific diseases.

• Technical Advancements:

  • Developed simple staining techniques.

  • Created protocols for pure culture techniques.

• Specific Major Discoveries:

  • $Bacillus\ anthracis$: The cause of Anthrax.

  • $Vibrio\ cholerae$: The cause of Cholera.

  • $Mycobacterium\ tuberculosis$: The cause of Tuberculosis ($TB$).

• Koch's Postulates: A four-step framework to determine the etiology of a disease:

  1. The same organism must be present in every case of the disease and absent from healthy individuals.

  2. The organism must be isolated from the diseased host and grown in a pure culture.

  3. The isolated organism must cause the same disease when inoculated into a healthy, susceptible host.

  4. The organism must be re-isolated from the newly infected, diseased experimental host.

Early Control of Infectious Disease

• Ignaz Semmelweis ($1818$-$1865$):

  • Discovered that handwashing significantly reduced maternal mortality rates from childbed fever (puerperal sepsis).

  • Historical data from $1841$-$1846$ showed the Midwives' ward had lower mortality than the Physicians' ward until hand hygiene was implemented.

• Joseph Lister ($1827$-$1012$):

  • Introduced aseptic techniques in surgery during the $1860s$.

  • Sanitized wounds and sterilized instruments using carbolic acid.

• Florence Nightingale:

  • Established and formalized aseptic techniques and sanitation within the field of nursing.

Classification and Taxonomy of Life

• Microbial Diversity: It is estimated that scientists are aware of only ~$1\%$ of all bacteria on Earth. Of that $1\%$, only ~$1\%$ are known human pathogens.

• Binomial Nomenclature:

  • A two-name system: $Genus\ species$.

  • Rules: Genus is capitalized, species is lowercase, and the entire name is italicized (e.g., $Staphylococcus\ aureus$).

• Taxonomic Hierarchy (Mnemonic: "Delightful King Philip Came Over For Great Spaghetti"):

  • Domain

  • Kingdom

  • Phylum

  • Class

  • Order

  • Family

  • Genus

  • Species

• Three Domains of Life:

  1. Bacteria: Unicellular prokaryotes.

  2. Archaea: Unicellular prokaryotes, often found in extreme environments (e.g., $Sulfolobus$).

  3. Eukarya: Includes unicellular and multicellular eukaryotes (Animals, Plants, Fungi, Protists).

• Definitions of Species and Strain:

  • Eukaryotic Species: A group of similar organisms capable of sexual reproduction.

  • Prokaryotic Species: Cells sharing physical characteristics, having at least $70\%$ DNA similarity and at least $97\%$ identical $16S\ rRNA$ sequence similarity.

  • Strain: Genetic variants of the same species, often resulting from mutations or gene transfer (e.g., $E.\ coli\ K-12$).

Microscopic Dimensions and Shapes

• Relative Sizes (Logarithmic Scale):

  • Atoms: $0.1\,nm$

  • Proteins/Lipids: $1\,nm$ - $10\,nm$

  • Viruses (Polio, Flu, Smallpox): $10\,nm$ - $100\,nm$

  • Bacteria/Mitochondria: $1\,\mu m$

  • Animal/Plant Cells: $10\,\mu m$ - $100\,\mu m$

  • Human Egg: $100\,\mu m$

  • Frog Egg: $1\,mm$

• Common Bacterial Shapes:

  • Coccus: Spherical

  • Bacillus: Rod-shaped

  • Vibrio: Curved, comma-shaped

  • Coccobacillus: Short, plump rod

  • Spirillum: Spiral

  • Spirochete: Long, thin, corkscrew spiral

• Scope of Microbiology Microbes:

  • Viruses and acellular pathogens

  • Bacteria and Archaea

  • Fungi

  • Protists (Algae and Protozoa like $Paramecium$)

  • Multicellular Parasites (Helminths)

Microscopy Techniques and Equipment

• Brightfield Microscope: Common light microscope using a solid cone of light. Samples are usually stained.

• Oil Immersion: Immersion oil has a refractive index similar to glass. It prevents light loss due to refraction, allowing more light to enter the objective lens, improving resolution.

• Summary of Light Microscopy Techniques:

  • Dark Field: Uses a modified condenser resulting in a hollow cone of light. Samples appear light on a dark background. Useful for unstained, live specimens.

  • Phase Contrast: Uses a phase plate to enhance brightness, shading, and contrast. Good for unstained live specimens.

  • Differential Interference Contrast (DIC/Nomarsky): Uses polarized light to provide a false $3D$ appearance.

  • Fluorescence: Uses fluorochromes and $UV$ light to detect specific molecules; very sensitive.

  • Confocal: Takes mathematical "slices" at different planes of focus to compile a clear $3D$ image, eliminating blur.

• Electron Microscopy:

  • Scanning Electron Microscope (SEM): Used for visualizing surfaces in high detail.

  • Transmission Electron Microscope (TEM): Used for visualizing internal structures (e.g., cross-sections of bacteria).

• Probe Techniques:

  • Scanning Tunneling Microscopy (STM): Uses a probe sharpened to a single atom; shoots electrons at the sample surface to visualize atoms; limited to conductive samples.

  • Atomic Force Microscopy (AFM): Probe is dragged or tapped along the surface; can visualize atoms in live or fixed samples under physiological conditions.

Principles of Epidemiology

• Definition: A branch of medical science dealing with the incidence, distribution, and control of disease in a population. It is the sum of factors controlling the presence or absence of a pathogen.

• Key Terminology:

  • Pathogen: A disease-causing agent.

  • True Pathogen: Causes disease in a healthy host.

  • Opportunistic Pathogen: Causes disease only when the host's defenses are compromised or when introduced to an unusual location.

  • Sporadic: Isolated cases.

  • Endemic: Spontaneously occurring in a specific region.

  • Epidemic: Sudden increase in cases in a region.

  • Pandemic: Worldwide epidemic.

  • Communicable: Transmissible between people.

  • Contagious: Easily transmissible between people.

  • Signs: Objective, measurable changes (e.g., fever, rash).

  • Symptoms: Subjective feelings reported by the patient (e.g., pain, nausea).

  • Acute: Rapid onset and resolution.

  • Chronic: Long-term, slow progression.

• Limitations of Koch's Postulates:

  • Multiple organisms can cause the same disease.

  • Asymptomatic carriers (agent present, but no disease).

  • Not all microbes can be grown in pure culture (e.g., $Treponema\ pallidum$ requires tissue culture).

  • Some pathogens are host-specific (e.g., Smallpox only infects humans, so no experimental animal host exists).

  • Latency (disease doesn't appear immediately).

Transmission and Reservoirs of Disease

• Reservoir: The natural habitat where a pathogen is found (animate or inanimate).

• Source: The specific dissemination point of the agent to the host.

  • Exogenous: External source (e.g., contaminated food).

  • Endogenous: Internal source (self-infection).

  • Example: For Botulism, the reservoir is soil ($Clostridium\ botulinum$), but the source is contaminated food.

• Direct Contact Transmission:

  • Person-to-person: Skin/mucous contact; fluids (e.g., HIV, MRSA, Mono).

  • Animal: Bites or scratches (e.g., Rabies).

  • Environment: Soil or water (e.g., Swimmer's ear, Anthrax via cuts).

• Indirect Contact Transmission:

  • Airborne: Respiratory droplets or aerosols (e.g., COVID-$19$, Measles, TB).

  • Vehicle: Fomites (contaminated objects like needles), food, or water (e.g., Salmonellosis, Cholera).

  • Vector (Biological): Pathogen reproduces/matures within an arthropod (e.g., Malaria in mosquitoes, Lyme in ticks).

  • Vector (Mechanical): Pathogen is physically carried on the exterior of the vector (e.g., flies landing on feces then food).

  • Vertical: From mother to child via placenta, vaginal delivery, or breast milk.

The Course and Measurement of Disease

• Five Stages of Infectious Disease:

  1. Incubation Period: Time between infection and first symptoms.

  2. Prodromal Phase: Early, mild symptoms develop.

  3. Acute Phase: The peak of the disease (highest pathogen levels).

  4. Period of Decline: Pathogen levels drop as the immune system or treatment takes control.

  5. Convalescent Phase: Recovery; pathogens may sometimes remain latent.

• Epidemiological Triangle: Disease occurs at the intersection of:

  1. Etiological Agent (Virus, Bacteria, etc.).

  2. Host Factors (Age, health, sex, occupation).

  3. Environmental Factors (Climate, water source, food).

• Quarantine: Period of confinement for those potentially infected. There are $9$ specifically quarantinable diseases in the US: Cholera, Diphtheria, Infectious TB, Plague, Smallpox, Yellow Fever, Viral Hemorrhagic Fevers, Pandemic Influenza, and SARS viruses.

• Morbidity Measurements:

  • Incidence: Number of new cases in a timeframe.

  • Prevalence: Total number of existing cases in a timeframe.

• Mortality Rates:

  • Crude Mortality: General death rate in a population.

  • Cause-Specific: Deaths due to a specific cause.

  • Infant Mortality: Deaths of children under age $1$ relative to live births.

  • Maternal Mortality: Deaths per $100,000$ live births from pregnancy-related causes.

  • Case Fatality Rate: Percentage of those diagnosed with a disease who die from it.

• Healthcare-Acquired Infections (HAIs):

  • Surgical site infections: $37\%$

  • Catheter-associated UTIs: $17\%$

  • Central line-associated bloodstream infections: $15\%$

  • Ventilator-associated events: $13\%$

  • $Clostridioides\ difficile$: $12\%$

  • MRSA bacteremia: $6\%$

Public Health Surveillance and Trends

• Surveillance Systems: Healthcare providers and labs report cases to state authorities; the CDC (National) and WHO (International) track data based on voluntary reporting.

• Emerging Disease Hot Spots: Factors contributing to emergence include ecological encroachment, international travel, and viral evolution/mutation (e.g., Ebola, SARS-CoV-$2$, MERS, H$1$N$1$ Influenza, Zika).