Microbiology: Bacteria, Viruses, and Infections

Posted on Nov 3, 2024 in Biology

Microbiology

Symbiotic Organisms

Symbiotic organisms are associated with other organisms, obtaining organic matter in exchange for benefits. For example, bacteria in the soil can fix atmospheric nitrogen for plants.

Parasitic Organisms

Parasitic organisms obtain organic matter from other organisms, causing disease. Examples include:

  • Bacteria in aerated soils and subsoils
  • Pathogenic microorganisms (disease-producing)

Louis Pasteur and Robert Koch

Louis Pasteur was a scientist who claimed that certain diseases were caused by specific microbes. Robert Koch discovered the causative agent of tuberculosis (Koch’s bacillus).

Infection and Contagion

Infection is the invasion of an organism by parasitic microorganisms. Contagion is the transfer of pathogenic microorganisms from an infected individual to a healthy one.

Pathogenicity, Virulence, and Toxins

  • Pathogenicity: The capacity of a microorganism to produce disease in a host.
  • Virulence: The intensity of the disease caused by an infectious agent.
  • Toxin: Poisonous substances produced by microorganisms.

Immune Response and Prevention

  • Immune: Mechanisms to combat infections.
  • Asepsis: Elimination of microorganisms from objects to prevent infection.
  • Antisepsis: Elimination of microorganisms from the body of patients using antiseptics.
  • Bacteriostatic: Laboratory-synthesized substances that prevent bacterial growth.
  • Antibiotics: Substances produced by microorganisms that inhibit bacterial growth and are harmless to infected organisms (e.g., penicillin).
  • Antivirals: Substances synthesized in the laboratory or extracted from specialized cells that inhibit viral growth (e.g., antivirals for AIDS).

Transmission of Infections

Airway

  • Tuberculosis (Koch’s bacillus invades lungs)
  • Pneumonia (Streptococcus pneumoniae – congested lung lobes)
  • Meningitis (Meningococcus – injury to the nervous system)

Gastrointestinal Tract

  • Gastroenteritis (Salmonella – inflammation of the stomach or intestine)
  • Cholera (Vibrio cholerae – severe gastroenteritis)
  • Poliomyelitis (Poliovirus – affects the central nervous system and bone development in children)

Contact

  • Sexually transmitted diseases (STDs): Syphilis (Treponema pallidum), Gonorrhea (Neisseria gonorrhoeae), AIDS
  • Tetanus and gangrene (Clostridium)
  • Herpes

Vector-borne

  • Rabies
  • Plague (fleas)
  • Malaria (mosquitoes)

Microorganisms and Food

Botulism (Clostridium botulinum) grows in canned foods.

Food Preservation Methods

  • Chilling
  • Freezing
  • Pasteurization (60°C)
  • Sterilization (120°C, 2 atm, 15 min)
  • Irradiation

Viruses

Viruses are acellular biological entities that reproduce within host cells as parasites. They are crystallizable and obligate intracellular parasites.

Virus Structure

  • Protein membrane
  • Capsid (composed of capsomeres)
  • Nucleic acid (viral genetic information)
  • Lipoprotein envelope

Life Cycle of Bacteriophage T4

Bacteriophage T4 is a virus that infects bacteria. It attaches to the bacterial wall and injects its DNA. The DNA can follow two pathways:

  • Lytic pathway: New viruses multiply and destroy the host cell.
  • Lysogenic pathway: Viral DNA integrates into the bacterial chromosome as a prophage.

Bacterial Reproduction

Bacteria reproduce by binary fission, a rapid process under optimal conditions. They can double every 20 minutes.

Genetic Recombination in Bacteria

Bacterial Conjugation

Conjugation involves two bacteria of different types. The F+ bacterium emits a cytoplasmic bridge (pilus) to the F- bacterium. The F factor is transferred from the donor to the recipient, which becomes F+.

Hfr Bacteria

In Hfr bacteria, the F factor fuses with the bacterial DNA. During conjugation, a DNA fragment containing plasmid and donor genes is transferred to the recipient. The recipient bacterium incorporates these genes into its DNA.

Bacterial Transformation

Transformation is a rare phenomenon where a DNA fragment from a dead bacterium enters another bacterium. The DNA escapes digestion and integrates into the recipient’s DNA.

Bacterial Transduction

Transduction is the exchange of genetic material between bacteria through a virus. It is linked to the lysogenic cycle of bacteriophages. The viral DNA (prophage) integrates into the bacterial DNA and is passed on to daughter cells during bacterial reproduction.