Microbial Control and Antibiotic Mechanisms

Microbial Growth Control
  • Focus on controlling the spread and growth of various microbes (bacteria, fungi, protozoa, viruses).
Historical Context
  • Early attempts to control microbes were made without understanding their existence.
  • Doctor Semmelweis (mid-1800s): Pioneered handwashing in hospitals to reduce postpartum infections (previously known as "peripheral fever").
    • Found higher infection rates in hospital births than home births, linked to lack of hand hygiene among doctors.
    • Suggested the link between medical practitioners and the spread of childbirth infections.
Methods of Microbial Control

  • Sterilization:

    • The highest level of microbial control, destroying all forms of life, including bacteria, fungi, protozoa, viruses, and their spores.
    • Cannot be applied to living tissues.
    • Used for lab and surgical equipment, often results in food quality degradation.

  • Disinfection:

    • Destroys vegetative cells but does not eliminate spores.
    • Suitable for surfaces but too harsh for living tissues.

  • Antisepsis:

    • Similar to disinfection but safe for living tissues (humans).
    • Destroys vegetative cells, but not spores.

  • Degermation:

    • Mechanical removal of microbes without killing them.
    • Example: Alcohol swab before injections.

  • Sanitation:

    • Reduces microbial load to safe levels as defined by health agencies.
Mechanism of Actions

  • Bacteriostatic:

    • Inhibits bacterial growth.

  • Bactericidal:

    • Kills bacteria but may leave intact cellular debris.

  • Bacteriolytic:

    • Kills bacteria and causes cell lysis, releasing cellular contents.
Exponential Death of Microbes
  • Microbial death rates are also exponential. The D-value represents the time to kill 90% of the population at a certain temperature or condition.
    • Example: In one minute, 90% of cells die; another minute kills 90% of the remaining cells.
Physical Methods of Control

  • Heat Treatment (Moist & Dry):

    • Moist Heat: Autoclaves use steam and high temperature for sterilization (121°C/20min).
    • Dry Heat: Incineration or hot air ovens can sterilize but are less efficient than moist heat.

  • Cold Temperature:

    • Slows metabolism (refrigeration); may kill pathogens during slow freezing.

  • Filtration:

    • Removes microbes from liquids or gases; can achieve sterilization depending on filter size.

  • Radiation:

    • Violet light or ionizing radiation damages DNA, sterilizing surfaces and equipment.
Chemical Methods of Control

  • Few achieve sterilization; mostly function as disinfectants or antiseptics.

  • Phenols: Effective disinfectants, disrupt cell membranes but can irritate skin.

  • Halogens (e.g., Chlorine, Iodine): Effective disinfectants, act by oxidizing cellular components.

  • Alcohols: Effective against vegetative bacteria; less effective against non-enveloped viruses and bacterial spores.

    • Requires water for effective action.

  • Oxidizing Agents (e.g., Hydrogen Peroxide): Effective antiseptics and disinfectants.

  • Antiseptics: Are broad and target pathogens while sparing host cells.

Antibiotics and Resistance

  • Antibiotics target specific bacterial functions (e.g., cell wall synthesis, protein synthesis).

    • Selective Toxicity: Ability to harm bacteria without harming human cells.
    • Categories include Factors such as cell wall inhibitors, protein synthesis inhibitors, DNA synthesis inhibitors, etc.

  • Resistance Mechanisms:

    • Bacteria can develop resistance through genetic mutations or acquisition of resistance genes.
    • Resistant strains can render treatment ineffective.

  • Therapeutic Index: Ratio indicating the safety of a drug; must be weighed during prescriptions to avoid toxicity to the patient.