Chapter 9: Controlling Microbial Growth in the Environment

Terminology of Microbial Control

• Sterilization: The complete removal or destruction of all forms of microbial life, including endospores and viruses.

• Disinfection: The elimination of most or all pathogens (except bacterial endospores) on inanimate objects.

• Antisepsis: The reduction of microbial numbers on living tissue.

• Sanitization: Lowering microbial counts to safe public health levels.

• Degerming: Mechanical removal of microbes from a limited area (e.g., skin before injection).

• Pasteurization: Use of heat to destroy pathogens and reduce spoilage organisms in food and beverages.

Basic Types of Antimicrobial Agents (Actions)

• Microbicidal agents: Kill microorganisms (e.g., bactericidal, fungicidal, virucidal).

• Microbistatic agents: Inhibit the growth of microorganisms without killing them (e.g., bacteriostatic).

Methods of Microbial Control

Physical Methods (6 Main Types)

• Heat: Denatures proteins and destroys membranes. Includes moist heat (autoclaving, boiling, pasteurization) and dry heat (oven, incineration).

• Cold: Slows metabolism and growth (refrigeration, freezing).

• Desiccation: Removal of water inhibits microbial growth.

• Filtration: Physically removes microbes from air or liquids using filters with defined pore sizes.

• Radiation: Damages DNA. Includes ionizing (gamma rays, X-rays) and non-ionizing (UV light) radiation.

• Osmotic Pressure: High concentrations of salt or sugar create hypertonic environments, causing plasmolysis.

Chemical Methods (8 Main Types)

• Alcohols: Denature proteins and disrupt membranes (e.g., ethanol, isopropanol).

• Halogens: Oxidize cell components (e.g., chlorine, iodine).

• Oxidizing Agents: Produce free radicals that damage cellular components (e.g., hydrogen peroxide).

• Phenolics: Disrupt cell membranes and denature proteins (e.g., triclosan, lysol).

• Surfactants: Lower surface tension, aiding in mechanical removal (e.g., soaps, detergents).

• Heavy Metals: Bind to proteins and inactivate them (e.g., silver, mercury).

• Aldehydes: Cross-link proteins and nucleic acids (e.g., formaldehyde, glutaraldehyde).

• Gaseous Agents: Denature proteins and DNA (e.g., ethylene oxide).

Biological Methods

• Enzymes: Biological catalysts that can degrade cell walls or membranes (e.g., lysozyme breaks down peptidoglycan in bacterial cell walls).

Chapter 10: Controlling Microbial Growth in the Body – Antimicrobials

Selective Toxicity

• Definition: The ability of an antimicrobial agent to harm the pathogen without harming the host.

• Example: Penicillin targets bacterial cell wall synthesis, which is absent in human cells.

Mechanisms of Antimicrobial Action (Six Types)

• Inhibition of cell wall synthesis (e.g., beta-lactams such as penicillins, cephalosporins).

• Inhibition of protein synthesis (e.g., tetracyclines, aminoglycosides).

• Disruption of cytoplasmic membrane (e.g., polymyxins, amphotericin B).

• Inhibition of nucleic acid synthesis (e.g., quinolones, rifampin).

• Inhibition of metabolic pathways (e.g., sulfonamides, trimethoprim).

• Inhibition of pathogen attachment or entry (e.g., antiviral drugs that block viral attachment).

Safety and Side Effects

• Toxicity: Some antimicrobials can cause damage to host tissues (e.g., nephrotoxicity, ototoxicity).

• Allergic reactions: Hypersensitivity to drugs (e.g., penicillin allergy).

• Disruption of normal microbiota: May lead to secondary infections (e.g., Clostridioides difficile colitis).

Resistance

• Mechanisms:

  • Enzymatic destruction or inactivation of the drug (e.g., beta-lactamases).

  • Alteration of drug target site.

  • Decreased permeability or increased efflux of the drug.

  • Bypass of the metabolic pathway targeted by the drug.

• Types:

  • Intrinsic resistance: Naturally occurring in certain species.

  • Acquired resistance: Due to mutation or horizontal gene transfer.

Chapter 14: Infection and Infectious Diseases

Types of Symbiosis

• Mutualism: Both organisms benefit (e.g., Escherichia coli in the human gut).

• Commensalism: One benefits, the other is unaffected (e.g., skin microbiota).

• Parasitism: One benefits at the expense of the other (e.g., pathogenic bacteria).

Resident Microbiota

• Definition: Microorganisms that normally reside on or in the human body without causing disease.

• Acquisition: Acquired during birth and from the environment.

• Examples: Skin, oral cavity, gut microbiota.

Opportunistic Pathogens

• Resident microbiota can become pathogenic if the host's immune system is compromised, or if they gain access to normally sterile body sites.

Reservoirs of Infection

• Human reservoirs: Infected individuals (symptomatic or asymptomatic).

• Animal reservoirs (zoonoses): Diseases transmitted from animals to humans.

• Nonliving reservoirs: Soil, water, food.

Contamination, Infection, Disease

• Contamination: Presence of microbes on surfaces or tissues.

• Infection: Invasion and multiplication of pathogens in the body.

• Disease: Damage or impairment of host tissue function due to infection.

Pathogenicity vs. Virulence

• Pathogenicity: The ability of a microorganism to cause disease.

• Virulence: The degree of pathogenicity; how severe the disease is.

Modes of Transmission

• Contact transmission: Direct (person-to-person), indirect (fomites), droplet.

• Vehicle transmission: Through air, water, or food.

• Vector transmission: Biological (e.g., mosquitoes) or mechanical (e.g., flies).

Healthcare-Associated Infections (HAIs)

• Definition: Infections acquired in healthcare settings.

• Types: Exogenous (from environment), endogenous (from patient's own microbiota), iatrogenic (from medical procedures).

Chapter 15: Innate Immunity

Overview

• Innate immunity is called 'innate' because it is present at birth and 'non-specific' because it does not target specific pathogens.

First Line of Defense

• Skin: Physical barrier, secretes antimicrobial peptides and sebum.

• Mucous membranes: Trap and remove microbes.

• Microbiome: Competes with pathogens for nutrients and space.

Second Line of Defense: Blood Components

• Blood cells:

  • Neutrophils: Phagocytosis and killing of microbes.

  • Eosinophils: Defense against parasites.

  • Basophils: Release histamine in inflammation.

  • Monocytes/Macrophages: Phagocytosis and antigen presentation.

  • Lymphocytes: Involved in adaptive immunity.

Phagocytosis

• Cells: Neutrophils, macrophages, dendritic cells.

• Six Steps:

  1. Chemotaxis

  2. Adherence

  3. Ingestion

  4. Maturation

  5. Killing

  6. Elimination (exocytosis)

Diapedesis

• Definition: Movement of leukocytes out of blood vessels into tissues.

• Conditions: Occurs during inflammation.

• Cells: Neutrophils, monocytes.

Non-Phagocytic Killing

• Cells: Eosinophils, natural killer (NK) cells, neutrophils.

• Mechanisms: Release of toxic granules, enzymes, or reactive oxygen species.

Interferons

• Definition: Proteins produced by cells in response to viral infection.

• Alpha and Beta Interferons: Induce antiviral states in neighboring cells.

Complement System

• Definition: A group of serum proteins that enhance immune responses (e.g., opsonization, lysis of pathogens).

Pyrogens

• Definition: Substances that induce fever.

• Producers: Can be produced by bacteria (e.g., endotoxins) or by the human host (e.g., interleukin-1).

• Pyrogenic Substances: Bacterial toxins, host cytokines.

Chapter 16: Adaptive Immunity

Overview

• Adaptive immunity is called 'adaptive' because it develops in response to specific antigens and 'specific' because it targets particular pathogens.

Five Attributes of Adaptive Immunity

• Specificity: Targets unique antigens.

• Inducibility: Activated by exposure to antigens.

• Clonality: Generates clones of specific lymphocytes.

• Unresponsiveness to self: Does not attack host tissues.

• Memory: Remembers previous encounters for faster response.

Cells of Adaptive Immunity

• B lymphocytes (B cells): Mature in bone marrow; produce antibodies.

• T lymphocytes (T cells): Mature in thymus; mediate cellular immunity.

Differences Between B and T Lymphocytes

• B cells: Humoral immunity, produce antibodies, mature in bone marrow.

• T cells: Cell-mediated immunity, do not produce antibodies, mature in thymus.

Organs of Operation

• B cells: Bone marrow, spleen, lymph nodes.

• T cells: Thymus, spleen, lymph nodes.

Antigens

• Definition: Molecules that elicit an immune response.

• Good antigens: Large, complex, foreign molecules (e.g., proteins, polysaccharides).

• Epitopes: Specific regions of antigens recognized by immune cells.

• Types:

  • Exogenous: Enter from outside the cell.

  • Endogenous: Generated within infected cells.

  • Autoantigens: Normal self-molecules.

Major Histocompatibility Complex (MHC)

• Definition: Cell surface proteins important for antigen presentation.

• MHC I: Found on all nucleated cells (except red blood cells).

• MHC II: Found on antigen-presenting cells (APCs) such as dendritic cells, macrophages, B cells.

T-Lymphocytes

• Types:

  • Helper T cells (CD4+): Activate B cells and other immune cells.

  • Cytotoxic T cells (CD8+): Kill infected or abnormal cells.

  • Regulatory T cells: Suppress immune responses to prevent autoimmunity.

• TCR (T cell receptor): Recognizes antigens presented by MHC molecules.

• Activation: Leads to proliferation and differentiation into effector cells.

• Clonal deletion: Removal of self-reactive T cells during development.

B-Lymphocytes

• BCR (B cell receptor): Recognizes specific antigens.

• Activation: Leads to proliferation and differentiation into plasma cells and memory B cells.

• Plasma cells: Secrete antibodies.

Antibodies

• Function: Neutralize pathogens, opsonize for phagocytosis, activate complement.

• Specificity: Each antibody binds a specific epitope.

• Classes:

  • IgM: First produced, short-lived.

  • IgG: Most abundant, long-lived, crosses placenta.

  • IgA: Found in mucosal areas and secretions.

  • IgE: Involved in allergic responses and defense against parasites.

  • IgD: Function not well understood, present on B cells.

Chapter 17: Immunity and Immunoassays

Types of Acquired Immunity

Immunization

• Definition: The process of inducing immunity by exposure to antigens (natural or artificial).

Herd Immunity

• Definition: Protection of susceptible individuals when a sufficient proportion of the population is immune.

• Needed percentage: Typically 85-95% depending on the disease.

Types of Vaccines

Immunotherapy

• Definition: Treatment using immune components (e.g., monoclonal antibodies) to enhance or suppress immune responses.

Serology and Serological Tests

• Serology: The study of antigen-antibody reactions in vitro.

• Principle: All serological tests are based on the specific binding between antigens and antibodies.