Microbiology Exam 3 Review: Biotechnology, Immunity, and Host-Pathogen Interactions

CH12 Biotechnology/Genetic Engineering

Overview of Genetic Engineering

Genetic engineering involves the manipulation of an organism's DNA to alter its characteristics or produce useful products. This is a foundational technique in modern microbiology and biotechnology.

• GMOs (Genetically Modified Organisms): Organisms whose genetic material has been artificially altered.

• Gene editing techniques: Methods such as CRISPR, restriction enzymes, and ligases are used to cut and modify DNA.

• Drug resistance markers: Genes that confer resistance to antibiotics, used for selection in cloning experiments.

• Electroporation and Hybridization: Techniques for introducing DNA into cells and detecting specific DNA sequences, respectively.

• FISH (Fluorescence In Situ Hybridization): A method for detecting and localizing specific DNA sequences on chromosomes.

• Insulin production: Example of recombinant protein production using genetically engineered bacteria.

• PCR (Polymerase Chain Reaction): Technique to amplify DNA segments for analysis.

• Cloning vectors: Plasmids and phage vectors used to carry foreign DNA into host cells.

Example: Production of human insulin by inserting the human insulin gene into Escherichia coli bacteria.

Equation:

$\text{PCR amplification:}~N = N_0 \times 2^n$

where $N$ is the number of DNA copies after $n$ cycles, and $N_0$ is the initial number of DNA molecules.

Microbiome

Definition and Functions

The microbiome refers to the collective genomes of microorganisms living in a particular environment, such as the human gut. These microbes play essential roles in health and disease.

• Functions: Digestion, synthesis of vitamins, immune modulation, and protection against pathogens.

• GALT (Gut-Associated Lymphoid Tissue): Immune tissue in the gut that interacts with the microbiome.

• Keystone species: Microbes that have a disproportionately large effect on their environment.

• Dysbiosis: Imbalance in the microbial community, associated with diseases such as obesity, autism, and cancer.

Example: Akkermansia muciniphila is a keystone species associated with gut health.

Host-Pathogen Interactions

Mechanisms and Outcomes

Not all bacteria are pathogens. Host-pathogen interactions determine the outcome of infection, including disease severity and immune response.

• Pathogenicity: Ability of a microbe to cause disease.

• Virulence factors: Molecules produced by pathogens that contribute to disease (e.g., toxins, adhesins).

• Exotoxins vs. Endotoxins: Exotoxins are secreted proteins; endotoxins are components of the bacterial cell wall (e.g., LPS).

• LD50: Dose required to kill 50% of a test population; measure of virulence.

• Immune evasion: Strategies used by pathogens to avoid host defenses.

Example: Staphylococcus aureus produces toxins that damage host tissues.

Innate Immunity

Physical and Chemical Barriers

Innate immunity provides the first line of defense against pathogens through non-specific mechanisms.

• Physical barriers: Skin, mucous membranes, and cilia.

• Cell types: Phagocytes (macrophages, neutrophils), dendritic cells, NK cells.

• Toll-like receptors (TLRs): Recognize pathogen-associated molecular patterns (PAMPs).

• Inflammation: Response to infection or injury, characterized by redness, heat, swelling, and pain.

Example: TLR4 recognizes bacterial lipopolysaccharide (LPS).

Adaptive Immunity, Immunotherapies, and Diagnostics

Specific Immune Responses and Clinical Applications

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

• Cell types: T cells (helper, cytotoxic), B cells (antibody production).

• MHC molecules: Present antigens to T cells; MHC I for cytotoxic T cells, MHC II for helper T cells.

• Antibody structure: Y-shaped proteins with variable and constant regions.

• Immunotherapies: Treatments that harness the immune system, such as CAR-T therapy and monoclonal antibodies.

• Diagnostics: ELISA, flow cytometry, and PCR-based methods for detecting pathogens and immune responses.

Example: Monoclonal antibodies are used to treat cancers and autoimmune diseases.

Equation:

$\text{Antibody-antigen binding:}~K_a = \frac{[AgAb]}{[Ag][Ab]}$

where $K_a$ is the association constant, $[AgAb]$ is the concentration of antigen-antibody complex, $[Ag]$ is antigen concentration, and $[Ab]$ is antibody concentration.

Table: Comparison of Innate and Adaptive Immunity

Feature	Innate Immunity	Adaptive Immunity
Specificity	Non-specific	Highly specific
Memory	None	Long-lasting
Cell Types	Phagocytes, NK cells	T cells, B cells
Response Time	Immediate	Delayed (days)
Major Molecules	Cytokines, complement	Antibodies, T cell receptors

Additional info:

• CAR-T therapy is a form of immunotherapy where T cells are engineered to target cancer cells.

• Spontaneous cancer remission may be linked to immune system activation.

• ELISA (Enzyme-Linked Immunosorbent Assay) is a common diagnostic tool for detecting antigens or antibodies.