Unit 3 Study Guide: Pathogenesis, Immunity, and Laboratory Techniques in Microbiology

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Epidemiology is the study of the distribution and determinants of health-related states and events in populations.
Key terms include: contagious (easily spread), biological vs. mechanical vectors (living vs. non-living transmitters), reservoirs (natural hosts), fomites (inanimate objects), and carriers (asymptomatic hosts).
Incidence refers to new cases in a population over a period, while prevalence is the total number of cases at a given time.

Modes of transmission include direct contact, indirect contact (via fomites), droplet, vector-borne, and vehicle-borne (e.g., water, food).
The chain of infection includes: infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host.
Stages of infectious disease: incubation, prodromal, illness, decline, and convalescence.
Virulence factors are molecules produced by pathogens that contribute to the pathogenicity and facilitate colonization, immune evasion, and host damage.

Pathogens must enter the host, adhere to tissues, evade immune defenses, and cause damage.
Examples of virulence factors: toxins, enzymes, capsules, and surface proteins.
Exotoxins are secreted proteins, while endotoxins are part of the outer membrane of Gram-negative bacteria (lipopolysaccharide, LPS).

Laboratory diagnosis involves specimen collection, culture, microscopy, and molecular methods.
Epidemiological tools include case definitions, surveillance, and outbreak investigation.

The innate immune system provides immediate, non-specific defense against pathogens.
First line of defense: physical barriers (skin, mucous membranes), chemical barriers (lysozyme, acidic pH), and mechanical removal (cilia, flushing action of fluids).
Second line of defense: cellular defenses (phagocytes, natural killer cells), inflammation, fever, and antimicrobial proteins (complement, interferons).

Neutrophils: phagocytose bacteria and fungi; most abundant leukocyte.
Macrophages: phagocytose pathogens and present antigens to T cells.
Eosinophils: combat multicellular parasites and participate in allergic responses.
Basophils: release histamine during allergic reactions.
Lymphocytes: include natural killer (NK) cells (innate) and B/T cells (adaptive).

Inflammation is characterized by redness, heat, swelling, and pain.
Key steps: vasodilation, increased permeability, migration of phagocytes, and tissue repair.
Phagocytosis involves chemotaxis, adherence, ingestion, digestion, and exocytosis of debris.

The complement system is a group of serum proteins that enhance phagocytosis, lyse pathogens, and promote inflammation.
Three activation pathways: classical, alternative, and lectin.
Outcomes: opsonization, membrane attack complex (MAC) formation, and inflammation.

The adaptive immune response is specific and has memory, involving B and T lymphocytes.
Humoral immunity (B cells): production of antibodies against extracellular pathogens.
Cell-mediated immunity (T cells): defense against intracellular pathogens and tumor cells.

Antigens are molecules recognized as foreign by the immune system.
B cells recognize antigens via B cell receptors (BCRs); T cells recognize processed antigens presented by MHC molecules.
Activation leads to clonal expansion and differentiation into effector and memory cells.

Antibodies (immunoglobulins) have variable regions for antigen binding and constant regions for effector functions.
Classes: IgG, IgM, IgA, IgE, IgD (each with distinct roles in immunity).

Vaccines stimulate adaptive immunity to provide long-term protection.
Types: live attenuated, inactivated, subunit, toxoid, conjugate, and nucleic acid vaccines.
Immune memory allows for a faster and stronger response upon re-exposure to the same pathogen.

Proper specimen collection is critical for accurate diagnosis; avoid contamination and ensure timely transport.
Common specimens: blood, urine, CSF, sputum, and swabs from infected sites.

Microscopy (light, phase-contrast, fluorescence) and staining (Gram, acid-fast) aid in identification.

CSF analysis is essential for diagnosing bacterial meningitis; look for increased WBCs, protein, and decreased glucose.
Rapid antigen tests and PCR can provide quick identification of pathogens.

Disc diffusion (Kirby-Bauer) and broth dilution methods determine susceptibility of bacteria to antibiotics.

These notes integrate foundational concepts from microbiology relevant to pathogenesis, immunity, and laboratory diagnostics, as outlined in the provided study guide.