Microbiology Exam 3 Study Guide: Infection, Immunity, and Epidemiology

Chapter 14: Infection, Infectious Diseases, and Epidemiology

Types of Symbiosis

Symbiosis refers to the close association between two different organisms. There are several types:

• Mutualism: Both organisms benefit. Example: Escherichia coli in the human gut produces vitamin K.

• Commensalism: One organism benefits, the other is unaffected. Example: Skin microbiota.

• Parasitism: One organism benefits at the expense of the other. Example: Pathogenic bacteria causing disease.

Normal Microbiota

The human body hosts a variety of microorganisms known as the normal microbiota, which are classified as:

• Resident microbiota: Permanent members of the body’s microbial community.

• Transient microbiota: Temporary, present for days or weeks.

Acquisition: Resident microbiota are acquired during birth and through contact with the environment.

Functions: The human microbiome aids in digestion, synthesizes vitamins, and protects against pathogens (microbial antagonism).

Opportunistic Pathogens

Normal microbiota can cause disease under certain conditions:

• Immune suppression

• Changes in the normal microbiota (e.g., antibiotics)

• Introduction into unusual body sites

Reservoirs of Infection

Reservoirs are sources of infectious agents:

• Human reservoirs: Carriers of disease (e.g., HIV, tuberculosis)

• Animal reservoirs: Zoonoses (e.g., rabies, Lyme disease)

• Nonliving reservoirs: Soil, water, food (e.g., botulism, cholera)

Portals of Entry and Exit

Pathogens enter and exit the body through specific portals:

• Skin

• Mucous membranes (respiratory, gastrointestinal, genitourinary)

• Placenta

• Parenteral route (injuries)

Definitions and Comparisons

• Infection: Invasion of host by pathogens

• Disease: Change from normal health due to infection

• Morbidity: Illness or disease state

• Pathogenicity: Ability to cause disease

• Virulence: Degree of pathogenicity

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

• Symptoms: Subjective, felt by patient (e.g., pain)

Biofilms and Infection

Biofilms are communities of microorganisms attached to surfaces, facilitating contamination and infection by protecting microbes from host defenses and antibiotics.

Koch’s Postulates

• Microbe must be found in every case of disease

• Microbe must be isolated and grown in pure culture

• Microbe must cause disease when introduced to healthy host

• Microbe must be re-isolated from the host

Limitations: Some pathogens cannot be cultured; some diseases are caused by multiple agents.

Etiology: Study of disease causation.

Virulence Factors

• Extracellular enzymes: Aid invasion (e.g., hyaluronidase)

• Toxins: Damage host (exotoxins, endotoxins)

• Adhesion factors: Help microbes attach to host cells

• Antiphagocytic factors: Prevent destruction by immune cells

Stages of Infectious Disease

• Incubation period

• Prodromal period

• Illness

• Decline

• Convalescence

Modes of Transmission

• Contact transmission: Direct, indirect, droplet

• Vehicle transmission: Air, water, food

• Vector transmission: Mechanical (passive), biological (active)

Droplet vs Airborne: Droplet is short-range; airborne is long-range.

Types of Diseases

• Acute: Rapid onset, short duration

• Subacute: Intermediate

• Chronic: Slow onset, long duration

• Latent: Inactive for a period

• Communicable: Spread person-to-person

• Noncommunicable: Not spread between people

Emerging and Re-emerging Diseases

Factors include microbial evolution, changes in human behavior, and environmental changes.

Epidemiology

Epidemiology is the study of disease distribution and determinants in populations. Methods include surveillance, statistical analysis, and outbreak investigation.

Epidemiological Curves

• Point source: Single exposure

• Continuous source: Ongoing exposure

• Propagated: Person-to-person spread

Incidence vs Prevalence

• Incidence: New cases in a time period

• Prevalence: Total cases at a given time

Pandemic, Epidemic, Endemic

• Pandemic: Global outbreak

• Epidemic: Sudden increase in cases

• Endemic: Constant presence in a population

Public Health

• Assessment

• Policy development

• Assurance

Nosocomial Infections

Hospital-acquired infections are influenced by patient susceptibility, hospital environment, and procedures. Prevention includes hand hygiene, sterilization, and isolation.

Chapter 15: Innate Immunity

Lines of Defense

• First line: Physical and chemical barriers (skin, mucous membranes)

• Second line: Internal defenses (phagocytes, inflammation, complement)

• Third line: Adaptive immunity (lymphocytes, antibodies)

Skin and Mucous Membranes

• Skin: Physical barrier, acidic pH, antimicrobial peptides

• Mucous membranes: Trap microbes, contain lysozyme, secrete mucus

Microbial Antagonism

Normal microbiota compete with pathogens, preventing colonization.

Blood Components

• White blood cells (WBCs): Neutrophils, lymphocytes, monocytes, eosinophils, basophils

• Function: Neutralize pathogens via phagocytosis, inflammation, and cytotoxicity

Natural Killer (NK) Cells

NK cells destroy infected or abnormal cells by releasing cytotoxic granules.

Complement Pathways

• Classical pathway: Activated by antibodies

• Alternative pathway: Activated by microbial surfaces

Interferons

Interferons are proteins that inhibit viral replication and activate immune cells.

Toll-like Receptors (TLRs)

TLRs recognize pathogen-associated molecular patterns (PAMPs) and trigger immune responses.

Chapter 16: Adaptive Immunity

Attributes of Adaptive Immunity

• Specificity

• Inducibility

• Clonality

• Unresponsiveness to self

• Memory

White Blood Cells in Adaptive Immunity

• B lymphocytes: Responsible for antibody-mediated (humoral) immunity

• T lymphocytes: Responsible for cell-mediated immunity

Specificity: Caused by unique antigen receptors.

Divisions of Adaptive Immunity

• Humoral immunity: Targets extracellular pathogens

• Cell-mediated immunity: Targets intracellular pathogens

Lymphatic System

The lymphatic system transports lymph and houses immune cells. Peyer's patches are lymphatic tissue in the small intestine. Lymph flow is directed by muscle contractions and valves.

Thymus and T Lymphocytes

The thymus is essential for T cell development. Types of T cells:

• Helper T cells (CD4+)

• Cytotoxic T cells (CD8+)

• Regulatory T cells

B Lymphocyte Specificity

B cells have unique antigen-binding receptors (immunoglobulins).

Immunoglobulin Classes

• IgG

• IgM

• IgA

• IgE

• IgD

Each class has distinct functions in immune responses.

Antigen-Antibody Complex

Binding of antibody to antigen leads to neutralization, opsonization, and complement activation.

Antigen Characteristics

Effective antigens are large, complex, and foreign to the host.

MHC Proteins

• Class I MHC: Present on all nucleated cells; alert cytotoxic T cells

• Class II MHC: Present on antigen-presenting cells; alert helper T cells

Cell-Mediated Immune Response

Cytotoxic T cells destroy infected cells via apoptosis.

Memory Cells

• Memory T cells: Provide rapid response upon re-exposure

• Memory B cells: Produce antibodies quickly upon re-exposure

Primary vs Secondary Immune Response

• Primary: First exposure, slower, less robust

• Secondary: Subsequent exposure, faster, stronger

Active vs Passive Immunity

• Active: Host produces own antibodies (leads to memory)

• Passive: Host receives antibodies (no memory)

• Natural: Through infection or maternal antibodies

• Artificial: Through vaccination or antibody therapy

Chapter 17: Immunization and Immune Testing

Types of Vaccines

• Attenuated: Live, weakened organisms; strong immunity, risk of reversion

• Inactivated: Killed organisms; safer, weaker immunity

• Toxoid: Inactivated toxins; require boosters

• Subunit: Purified antigens; safe, less immunogenic

• Conjugate: Linked antigens; improved response in children

Adjuvants: Added to inactivated and subunit vaccines to enhance immune response.

History of Vaccination

Edward Jenner performed the first vaccination using cowpox to prevent smallpox.

Germ Theory: Diseases are caused by microorganisms.

Routine Vaccination

• Benefits: Prevents disease, herd immunity

• Risks: Adverse reactions, rare complications

Contact immunity: Immunity in unvaccinated individuals due to spread of vaccine virus.

Herd immunity: Protection of population when enough individuals are immune.

Active Immunization vs Passive Immunotherapy

• Active: Long-lasting, memory

• Passive: Immediate, short-term, no memory

Passive immunotherapy involves administration of pre-formed antibodies.

Serology and Immune Testing

Serology is the study of blood serum for antibodies. Uses include diagnosis and monitoring immunity.

Test	Purpose	Example
Immunochromatographic assay	Rapid detection	Pregnancy test
Fluorescent antibody test	Detect antigens/antibodies	Direct: Detects antigen; Indirect: Detects antibody

Chapter 18: Immune Disorders (HIV/AIDS Focus)

AIDS and HIV

• AIDS: Acquired Immunodeficiency Syndrome; defined by severe immune deficiency

• Disease vs Syndrome: Disease has specific cause; syndrome is a collection of symptoms

• HIV: Retrovirus infecting helper T cells; replicates via reverse transcription

• Immune Evasion: High mutation rate, attacks immune cells

Helper T cell population declines as AIDS progresses.

Risk and Prevention Behaviors

• Risk: Unprotected sex, sharing needles, blood transfusions, mother-to-child transmission

• Prevention: Safe sex, clean needles, screening blood, antiretroviral therapy

Additional info: These notes expand brief learning objectives into full academic explanations, suitable for exam preparation. For more detail, refer to textbook chapters and review questions.