Chapter 7. Microbial Genetics

Regulation of Prokaryotic Transcription

Microbial genetics explores how microorganisms inherit and regulate genetic information, with a focus on prokaryotic transcription control mechanisms.

• Inducible and Repressible Operons: Inducible operons (e.g., lac operon) are activated in response to specific substrates, while repressible operons (e.g., trp operon) are inhibited when the end product is abundant.

• Transcriptional Control: The lac operon is regulated by the presence of lactose, which inactivates the repressor and allows transcription. The trp operon is repressed when tryptophan is present.

• Diagram Example: A diagram of the lac operon typically shows the promoter, operator, structural genes, and the repressor protein.

Definition: An operon is a cluster of genes under the control of a single promoter and operator, allowing coordinated regulation.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can affect protein function and microbial traits.

• Types of Mutations: Point mutations (substitution, insertion, deletion), frameshift mutations, and silent mutations.

• Effects: Mutations may result in altered protein function, loss of function, or no effect (silent).

• Repair Mechanisms: Cells possess DNA repair systems such as nucleotide excision repair and mismatch repair.

Horizontal Gene Transfer

Microbes exchange genetic material through horizontal gene transfer, increasing genetic diversity.

• Transformation: Uptake of naked DNA from the environment.

• Transduction: Transfer of DNA via bacteriophages.

• Conjugation: Direct transfer of DNA between cells via a pilus.

• Components: Plasmids, F factor, Hfr cells.

Example: Escherichia coli can acquire antibiotic resistance genes via conjugation.

Chapter 9. Controlling Microbial Growth in the Environment

Definitions and Methods

Controlling microbial growth is essential for preventing infection and maintaining sterile environments.

• Key Terms: Sterilization (complete destruction of all microbes), disinfection (elimination of most pathogens), antisepsis (removal of pathogens from living tissue), sanitation (reducing microbial load to safe levels).

• Physical Methods: Heat (moist and dry), filtration, radiation, and cold.

• Chemical Methods: Use of disinfectants, antiseptics, and sterilants.

Microbial Resistance

• Microbial Resistance: Some microbes are more resistant to antimicrobial agents due to structural or metabolic features.

• Basis for Resistance: Endospores, mycobacteria, and prions are highly resistant.

Classification of Methods

• Microbicidal vs. Microbistatic: Microbicidal methods kill microbes; microbistatic methods inhibit growth.

• Examples: Autoclaving is microbicidal; refrigeration is microbistatic.

Chapter 10. Controlling Microbial Growth in the Body: Antimicrobial Drugs

Antimicrobial Drug Actions

Antimicrobial drugs are used to treat infections by targeting specific microbial processes.

• Mechanisms: Inhibition of cell wall synthesis, protein synthesis, nucleic acid synthesis, metabolic pathways, and cell membrane integrity.

• Broad-spectrum vs. Narrow-spectrum: Broad-spectrum drugs target a wide range of microbes; narrow-spectrum drugs are specific.

• Examples: Penicillins (cell wall synthesis), tetracyclines (protein synthesis).

Drug Resistance

• Mechanisms: Enzymatic degradation, altered targets, efflux pumps.

• Prevention: Appropriate use, combination therapy, and stewardship.

Chapter 14. Infection, Disease, and Epidemiology

Definitions and Types

Understanding infection and disease is crucial for epidemiology and public health.

• Opportunistic Pathogens: Cause disease in immunocompromised hosts.

• Superinfection: Secondary infection by resistant microbes.

• Etiology: Study of disease causation.

Normal Microbiota

• Types: Resident (permanent) and transient (temporary) microbiota.

• Acquisition: Birth, environment, and contact.

Chapter 15. Innate Immunity

Non-Specific Defenses

Innate immunity provides immediate, non-specific defense against pathogens.

• First Line Defenses: Skin, mucous membranes, secretions, and normal microbiota.

• Second Line Defenses: Phagocytes, inflammation, fever, and antimicrobial proteins.

Phagocytosis and Inflammation

• Phagocytosis: Engulfment and destruction of microbes by leukocytes.

• Inflammation: Redness, heat, swelling, pain; involves cytokines and immune cells.

Antimicrobial Proteins

• Interferons: Proteins that inhibit viral replication.

• Complement System: Series of proteins that enhance immune responses.

Chapter 16. Specific Defenses: Adaptive Immunity

Antigens and Immune Response

Adaptive immunity is characterized by specificity and memory, involving lymphocytes and antibodies.

• Antigen: Substance that elicits an immune response.

• B Cells: Produce antibodies; responsible for humoral immunity.

• T Cells: Mediate cellular immunity; include helper, cytotoxic, and regulatory T cells.

Antibody Structure and Function

• Antibody Classes: IgG, IgM, IgA, IgE, IgD.

• Functions: Neutralization, opsonization, complement activation.

Clonal Selection and MHC

• Clonal Selection: Activation and proliferation of specific lymphocytes upon antigen exposure.

• MHC Molecules: Present antigens to T cells; Class I (all nucleated cells), Class II (antigen-presenting cells).

Comparison Table: Innate vs. Adaptive Immunity

Key Equations

• Rate of Microbial Death:

Where = number of surviving microbes at time , = initial number, = death rate constant.

• Antibody-Antigen Binding:

Additional info: Some definitions and examples have been expanded for clarity and completeness. The comparison table and equations are inferred from standard microbiology curriculum.