Applied Microbiology - Control of Microbes

Factors Affecting Effectiveness of Sterilization and Disinfection:

• Concentration of the Agent: Higher concentrations often result in greater effectiveness against microorganisms.

• Exposure Time: Longer exposure times typically enhance the effectiveness of the sterilizing or disinfecting agent.

• Temperature: Increased temperatures can accelerate the activity of disinfectants and sterilants, making them more effective.

• Nature of the Microbial Load: Different microorganisms (bacteria, viruses, fungi) have varying levels of resistance; pathogens with thick cell walls or spore-forming capabilities may require different approaches.

• Organic Matter Presence: Presence of organic materials like blood or biowaste can inhibit the action of certain disinfectants, reducing their effectiveness.

• Surface Material: Porous vs. non-porous surfaces facilitate different levels of microbial survival and disinfectant penetration.

Common Types of Sterilization & Disinfection and Their Mechanisms:

• Heat Sterilization: Utilizes moist heat (autoclaving at 121°C for 15-30 minutes) or dry heat (incineration) to kill all microbial life through protein denaturation.

• Chemical Disinfection: Involves applying chemicals like alcohols (e.g., ethanol) or chlorine compounds which disrupt cellular membranes and denature proteins, effectively killing microorganisms.

• Radiation: UV or gamma radiation damages microbial DNA, rendering the organisms unable to reproduce.

• Filtration: Physically removes microbes from liquids or air by passing them through filters with micro-sized pores.

Sterilization: Complete removal of all viable microorganisms, including spores.

• Example: Autoclaving surgical instruments at high pressure and temperature (121°C) to ensure complete sterility.

Disinfection: Process of eliminating or reducing harmful microorganisms on inanimate objects.

• Example: Using bleach solution (sodium hypochlorite) to disinfect surfaces in a medical setting.

Sanitization: Reducing microbial population to safe levels to meet public health standards.

• Example: Washing dishes in a dishwasher that uses high temperatures to sanitize and eliminate harmful bacteria.

Antisepsis: Prevention of infection by applying antiseptics to living tissues.

• Example: Using iodine-based antiseptics on the skin before surgery to reduce the risk of infection.

Advantages & Disadvantages of Sterilization, Disinfection, Sanitization & Antisepsis:

• Advantages:

  • Sterilization is the most thorough method, ensuring no viable organisms remain.

  • Disinfection is effective for reducing pathogens quickly in non-sterile environments.

  • Antisepsis is crucial for limiting infections during medical procedures.

• Disadvantages:

  • Sterilization can be costly and time-consuming, applying only to surgical tools.

  • Some disinfectants may leave harmful residues or require longer contact times.

  • Antiseptics may cause skin irritation or allergies.

Scenario for Use: Surgical theaters use sterilization for instruments to prevent post-operative infection; classrooms utilize disinfection methods to clean surfaces and minimize the spread of viruses.

Examples of Disinfectants Used to Reduce Microorganisms from Surfaces:

• Phenolics: Triclosan, used in household disinfectants and soaps.

• Alcohols: Isopropyl alcohol, effective for surface disinfection and skin antisepsis.

• Halogens: Iodine and chlorine compounds, commonly used in swimming pool sanitization.

• Heavy Metals: Silver nitrate or copper sulfate, historically used in water purification.

• Quaternary Ammonium Compounds: Benzalkonium chloride, used in surface disinfectants and cleaning wipes.

• Aldehydes: Formaldehyde, used for tissue preservation in laboratories.

Major Mechanisms of Action Used by Antimicrobial Drugs:

• Inhibition of Cell Wall Synthesis: Preventing bacteria from forming a protective wall, leading to cell lysis.

• Disruption of Protein Synthesis: Targeting bacterial ribosomes to obstruct protein production critical for survival.

• Interference in Metabolic Pathways: Blocking essential metabolic processes (e.g., folic acid synthesis).

• Inhibition of Nucleic Acid Synthesis: Preventing replication and transcription of DNA or RNA.

Mechanisms Behind Antimicrobial Resistance:

• Resistance may arise through mutations in microbial DNA or acquisition of resistance genes from other microbes.

• Mechanisms include drug degradation by enzymes, altered binding sites, and active efflux pumps that expel drugs from the cell.

Transmission of Antimicrobial Resistance:

• Resistance genes can be transmitted via horizontal gene transfer mechanisms: transformation (uptake of free DNA), transduction (bacteriophage-mediated gene transfer), or conjugation (transfer through direct contact). This enables rapid dissemination of resistance traits among bacterial populations.