Biomedical Applications: Vaccines, Diagnostics, Therapeutics, and Antimicrobial Drugs

Chapter 14: Biomedical Applications

Herd Immunity

Herd immunity is a critical concept in public health and microbiology, describing how the resistance of a population to the spread of infectious disease is achieved when a high proportion of individuals are immune, either through previous infection or vaccination.

• Immunity: The state or quality of being resistant to a particular infectious disease or pathogen.

• Herd immunity: Resistance to the spread of an infectious disease within a population, based on pre-existing immunity of a high proportion of individuals.

• Benefit: The fewer disease-susceptible people in a community, the harder it is for a pathogen to be transmitted to a susceptible host.

• Threshold: Most pathogens require approximately 85% immunity rate in the population to achieve herd immunity.

• Example: Widespread vaccination against measles prevents outbreaks even among those who cannot be vaccinated.

Immunization Programs

Immunization programs are designed to increase population immunity and prevent the spread of infectious diseases.

• CDC Recommendations: In the US, the Centers for Disease Control and Prevention (CDC) provides vaccination schedules and recommendations.

• Childhood Vaccination: Children typically receive 58-78 shots during childhood, with many administered within the first 15 months of life.

Vaccines

Vaccines are biological preparations that provide immunity to specific infectious diseases. They can be administered via injection, inhalation, or ingestion.

• Components:

  • Weakened (attenuated) microbe

  • Fragments of the microbe

  • Isolated inactivated toxin

  • Genetically manufactured portion of the microbe

  • Adjuvants (e.g., aluminum), preservatives, dyes, animal material, etc.

• Immunological Memory: Vaccines stimulate the adaptive immune system to create memory B and T cells, providing long-term protection.

• Antibody Peak: It typically takes about two weeks for antibody levels to reach their peak after vaccination.

Vaccine Types

Vaccines are categorized by their formulation and method of production.

• Live Attenuated Vaccines: Contain live pathogens that have been weakened so they do not cause disease but are still infectious.

  • Examples: Varicella-zoster (chickenpox), measles, mumps, rubella (MMR), rotavirus, oral polio (OPV).

  • Benefit: Stimulate potent immunological responses and long-lived memory.

  • Drawbacks: Risk for immunocompromised individuals, possible reversion to infectious form, must be refrigerated.

• Inactivated Vaccines: Consist of whole pathogens that have been killed or inactivated and cannot reproduce.

  • Includes whole-agent and subunit vaccines.

  • Require adjuvants to enhance immune response.

  • Examples: Hepatitis A, influenza, polio, rabies.

  • Drawbacks: Boosters required for full immunity, stable at room temperature.

• Toxoid Vaccines: Contain purified and inactivated toxins.

  • Examples: Tetanus and diphtheria (DTaP, Tdap).

• Viral Vector Vaccines: Use a modified virus to deliver genetic material encoding antigens to host cells.

  • Example: Adenovirus-based COVID-19 vaccines.

  • Concern: Potential for genetic material to enter the nucleus and integrate into host DNA.

• Messenger RNA (mRNA) Vaccines: Provide instructions for cells to produce viral proteins, stimulating an immune response.

  • mRNA remains in the cytoplasm and is degraded after translation.

  • Example: COVID-19 mRNA vaccines.

  • Concerns: Theoretical risks regarding reverse transcription and integration, but mRNA does not enter the nucleus.

Chapter 15: Antimicrobial Drugs

Antimicrobial Drugs: Classification and Mechanisms

Antimicrobial drugs are therapeutic compounds used to kill or inhibit the growth of microbes. They are classified based on the type of pathogen they target and their mechanism of action.

• Types of Antimicrobial Drugs:

  • Antibacterial drugs: Treat bacterial infections.

  • Antiviral drugs: Target viral infections.

  • Antifungal drugs: Work against fungal infections.

  • Antiparasitic drugs: Treat protozoan and helminthic (worm) infections.

• Mechanisms of Action:

  • Bacteriostatic: Prevent bacteria from growing.

  • Bactericidal: Actively kill bacteria.

  • Broad-spectrum: Effective against both Gram-negative and Gram-positive bacteria (e.g., quinolones).

  • Narrow-spectrum: Target a limited range of bacteria (e.g., bacitracin, vancomycin).

Antibacterial Drugs: Cellular Targets

Antibacterial drugs are grouped by their cellular targets within bacterial cells.

Target	Examples of Drugs	Action
Cell wall synthesis	Penicillins, Cephalosporins, Carbapenems, Monobactams, Glycopeptides	Usually bactericidal
Plasma membrane	Polypeptide drugs	Usually bactericidal
Nucleic acid synthesis	Quinolones, Rifamycins	Usually bactericidal
Protein synthesis	Macrolides, Tetracyclines, Aminoglycosides, Lincosamides, Phenicols	Usually bacteriostatic
Folic acid synthesis	Sulfa drugs, Trimethoprim	Usually bacteriostatic

Antiviral Drugs: Mechanisms of Action

Antiviral drugs are classified according to the viral activity they target. They are essential for treating viral infections and often work by interfering with specific stages of the viral life cycle.

• Attachment: Prevents the virus from binding to host cells.

• Penetration: Blocks entry of the virus into the host cell.

• Uncoating: Inhibits the release of viral genetic material inside the host cell.

• Viral replication and assembly: Disrupts the synthesis and assembly of viral components.

• Viral release: Prevents the release of new viral particles from infected cells.

• Interferons: Stimulate immune responses against viruses.

Additional info:

• Optimal immunological memory from vaccines may require booster doses and time for the adaptive immune system to generate effective memory cells.

• Vaccine failure can occur due to improper storage, administration, or individual immune response variability.

• Antimicrobial drugs must be selected based on the pathogen type and the drug's spectrum of activity to minimize resistance and maximize efficacy.