Bacteria and Disease

Bacteria and the Rest of Life

• Two types of life: Eukaryotic and prokaryotic.
• All bacteria are prokaryotes.
• Eukaryotes (all other living organisms) have a more complex cellular structure.

Prokaryotic vs. Eukaryotic

• Bacteria (Prokaryotes):
  • Unicellular (always one cell).
  • Simpler structure.
  • No nuclear membrane enclosing the nuclear material (no distinct nucleus).
  • No discrete organelles in the cytoplasm (except ribosomes).
  • Reproduce by binary fission (splitting into daughter cells, creating clones).

Importance of Microscopes in Nursing

• Microscopes allow identification of invisible pathogens causing disease.
• Lack of visibility can lead to underestimation of the problem.
• Asymptomatic infections are possible.
• Infection control mechanisms (masks, gloves, hand washing) have saved lives.
• New infections continually emerge, often due to genetic changes in bacteria.
  • Example: Vancomycin-resistant Enterococcus (VRE).
  • Example: Methicillin-resistant Staphylococcus aureus (MRSA).

Germ Theory of Disease - Koch's Postulates

• Important concept for understanding how bacteria and viruses cause disease.
• Developed by German microbiologist Robert Koch.
• Experiment with Bacillus anthracis (causes anthrax):
  1. Bacteria taken from a diseased animal.
  2. Bacteria grown in a pure culture.
  3. Culture injected into a different animal.
  4. The animal develops the same symptoms and dies.
  5. The same bacteria is found in the dead animal.
• Koch's postulates don't always hold true due to impediments.

Clinical Practice

• Taking cultures from patients (wounds, blood, fluids).

Steps in Koch's Postulates (Expanded)

1. Cow shows signs of a disease.
2. Blood is extracted from the diseased cow.
3. A sample of extracted blood is placed on a microscope slide and examined to isolate bacteria.
4. The blood is examined under a microscope to observe and classify the bacteria based on its features.
5. The bacteria is extracted from the blood sample:
6. The specific type of bacterium is isolated and cultured in a controlled environment to ensure that it grows without contamination.
7. The daughter cells from the pure culture are injected into a suitable animal.
8. The injected animal develops the same disease symptoms as the original cow.
9. Again, blood is taken from the infected animal after it either dies or shows symptoms.
10. The process is repeated: the microorganism found during the experiment from the newly infected animal allows researchers to confirm that this microorganism is the etiological cause of the specific disease.

Significance

• Demonstrates the link between symptoms and bacteria causing the disease.

Naming of Bacteria

• All bacteria have two names: genus and species.
  • Analogy: Canis (genus) for dog-like animals (foxes, wolves, dogs).
  • Canis domesticus (species) for domestic dogs.
• Example: Escherichia coli (E. coli).
  • Genus: Escherichia.
  • Species: coli.
• Strains or subspecies can be added (e.g., enterotoxigenic E. coli).
• Naming convention: Genus (capitalized), species (lowercase).

Historical Context of Naming

• Bacteria were named before standardized rules were developed.
• Genus names can have various origins:
  • Named after a person (e.g., Escherichia after Theodor Escherich)
  • Based on shape (e.g., Bacillus).
  • Based on location (e.g., E. coli found in the colon).
  • Based on the disease it causes (e.g., Clostridium tetani causes tetanus).
• Lack of standardization makes understanding names difficult.

Diseases and Causation

• A disease can be caused by multiple organisms or factors.
  • Example: Pneumonia can be caused by bacteria (Streptococcus, Pseudomonas), viruses (influenza, H5N1, SARS), fungi, or chemicals.
• Need to be careful about associating diseases with single organisms.
  • Example: Hepatitis can be caused by poisons, fungi, or viruses.
• Pneumonia = inflammation of the lungs.
  • Involves smaller functional units (alveoli) and bronchioles.
  • Alveoli become plugged with thick fluid.
• Diagrammatic representation:
  • Normal alveoli vs. alveoli filled with fluid and inflamed.