Microbiology Exam Review: Disinfection, Immunology, and Pathogenic Microorganisms

Disinfectants, Antiseptics, and Sterilization

Definitions and Differences

Disinfectants and antiseptics are chemical agents used to control microbial growth, but they differ in their application and potency.

• Disinfectants: Chemicals used on non-living surfaces to destroy or inhibit microorganisms. Not safe for use on living tissue.

• Antiseptics: Chemicals safe for use on living tissue to reduce or inhibit microbial growth.

• Key Difference: Disinfectants are generally more potent and toxic than antiseptics.

• Concentration Effects: Some agents are less effective at higher concentrations due to protein coagulation or other mechanisms.

Factors Affecting Disinfectant Activity

• Contact time

• Concentration of agent

• Presence of organic matter

• Temperature and pH

AOAC Use-Dilution Test

This is a standardized test to evaluate the efficacy of disinfectants. It involves exposing stainless steel carriers contaminated with bacteria to the disinfectant and assessing microbial survival.

• 3 volumes: Refers to the number of replicate tests performed.

• Computation: The percentage of carriers showing no growth is calculated.

Radiation in Microbial Control

• Ionizing radiation: Includes gamma rays and X-rays; causes DNA damage and is used for sterilization.

• Nonionizing radiation: Includes UV light; causes thymine dimers in DNA, used for surface disinfection.

Anderson Samplers

Used to sample airborne microorganisms, especially in hospital and laboratory settings.

Applications of Disinfection Methods

Best Agents for Specific Applications

• Antimicrobial hand wash: Alcohol-based hand rubs, chlorhexidine

• Semi-critical instrument disinfection: Glutaraldehyde, hydrogen peroxide

• Counter or other small surface disinfection: Quaternary ammonium compounds

• Antimicrobial mop water for large areas: Phenolics, bleach

• Sterilization of heat-labile plastics: Ethylene oxide gas, gamma irradiation

Antimicrobial Drugs and Their Characteristics

Drug Classes and Mechanisms

Antimicrobial drugs are classified based on their targets and mechanisms of action.

• Beta-lactam antibiotics: Inhibit cell wall synthesis (e.g., penicillins, cephalosporins)

• Antituberculosis drugs: Isoniazid, ethambutol, rifampin; often used in combination

• Protein synthesis inhibitors: Aminoglycosides, tetracyclines, macrolides

• DNA synthesis inhibitors: Quinolones (inhibit DNA gyrase), metronidazole

• RNA synthesis inhibitors: Rifampin

• Antiviral agents: Reverse transcriptase inhibitors, protease inhibitors

Examples and Applications

• Streptomycin: Aminoglycoside used for tuberculosis

• Penicillin: Beta-lactam antibiotic, effective against Gram-positive bacteria

• Quinolones: Used for urinary tract infections

Side Effects

• Tetracyclines: Can cause "black hairy tongue" and permanent teeth staining

Immunology: Cells, Tissues, and Functions

Types of Immune Cells

• Phagocytic cells: Neutrophils, macrophages

• Lymphocytes: B cells (produce antibodies), T cells (cell-mediated immunity)

• Plasma cells: Differentiated B cells that secrete antibodies

• Mast cells: Involved in allergic responses

Inflammation and Complement System

• Cardinal signs of inflammation: Redness, heat, swelling, pain

• Complement pathways: Classical, alternative, lectin; all lead to pathogen lysis

Primary and Secondary Lymphoid Tissues

• Primary: Bone marrow, thymus

• Secondary: Lymph nodes, spleen, tonsils

Types of Immunization

• Artificially acquired active: Vaccination

• Artificially acquired passive: Injection of antibodies

• Naturally acquired active: Infection

• Naturally acquired passive: Maternal antibodies

Immunoglobulins and Antigen Recognition

Classes of Immunoglobulins

• IgG: Most abundant, crosses placenta

• IgM: First produced in response

• IgA: Found in mucosal areas

• IgE: Involved in allergies

• IgD: B cell receptor

MHC Molecules

• MHC Class I: Present on all nucleated cells; present antigens to CD8+ T cells

• MHC Class II: Present on antigen-presenting cells; present antigens to CD4+ T cells

Passive Immunity

• Transfer of antibodies from another individual

Serological Tests and Hypersensitivity

Serological Test Types

• Immunoelectrophoresis: Separates proteins based on charge and reaction with antibodies

• Hemagglutination: Clumping of red blood cells

• Ouchterlony: Double diffusion in agar

• ELISA: Enzyme-linked immunosorbent assay

• Western blot: Protein detection

Hypersensitivity Types

• Type I: Immediate (allergy)

• Type II: Cytotoxic

• Type III: Immune complex

• Type IV: Delayed (cell-mediated)

Transplantation Terms

• Autograft: From same individual

• Isograft: From genetically identical individual

• Allograft: From same species

• Xenograft: From different species

Immunosuppressive Drugs

• Corticosteroids

• Cyclosporine

• Azathioprine

Autoimmune Diseases

Examples and Causes

• Type 1 diabetes: Destruction of pancreatic beta cells

• Multiple sclerosis: Demyelination of neurons

• Systemic lupus erythematosus: Autoantibodies against nuclear antigens

• Graves' disease: Hyperthyroidism due to autoantibodies

• Rheumatoid arthritis: Chronic joint inflammation

Immunodeficiency Disorders

Examples

• SCID: Severe combined immunodeficiency

• DiGeorge syndrome: Thymic aplasia

• Bruton-type agammaglobulinemia: Lack of B cells

Lancefield Typing

Purpose and Use

Lancefield typing classifies streptococci based on cell wall carbohydrates. Used to identify pathogenic species.

Pathogenic Microorganisms and Virulence

Key Bacterial Pathogens

Below is a table summarizing important bacteria, their unique properties, and associated diseases.

Bacterium	Unique Properties	Diseases Caused
Clostridium botulinum	Produces botulinum toxin	Botulism
Bacillus anthracis	Spore-forming, capsule	Anthrax
Streptococcus pyogenes	Group A, beta-hemolytic	Pharyngitis, rheumatic fever
Staphylococcus aureus	Coagulase positive	Skin infections, toxic shock
Mycobacterium tuberculosis	Acid-fast, slow-growing	Tuberculosis
Actinomyces	Filamentous, anaerobic	Actinomycosis
Streptomyces	Produces many antibiotics	Non-pathogenic, source of drugs
Nocardia	Partially acid-fast	Nocardiosis
Corynebacterium diphtheriae	Diphtheria toxin	Diphtheria

Importance of Streptomyces

• Major source of antibiotics such as streptomycin, tetracycline, and chloramphenicol

Additional info:

• Some content inferred for completeness, such as specific examples of drugs and pathogens.

• Equations are not directly relevant to this content, but immunology and microbiology may use formulas for dilution and concentration calculations, e.g.:

$C_1V_1 = C_2V_2$ (Dilution equation)