Control of Microbial Growth Flashcards
Presence of microbial contamination, often leading to infection.
Sepsis
Absence of significant contamination, crucial in medical settings.
Asepsis
Complete elimination of all microbial life, including spores.
Sterilization
Targets Clostridium botulinum spores in food processing.
Commercial Sterilization
Kills vegetative microbes on nonliving surfaces (e.g., using bleach).
Disinfection
Kills vegetative microbes on living tissue (e.g., using alcohol on skin).
Antisepsis
Physically removes microbes from a small area (e.g., handwashing).
Degerming
Chemicals that kill microbes (e.g., disinfectants).
Biocide/Germicide
Inhibits microbial growth without killing them (e.g., refrigeration).
Bacteriostasis
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“Factors Influencing Microbial Death by Antimicrobial Agents”
- Number of Microbes – A higher microbial load takes longer to eliminate.
- Environmental Influences – Organic matter, biofilms, temperature, and pH can protect microbes from antimicrobial agents.
- Biofilms – Microbes in biofilms are more resistant due to their protective matrix.
- Time of Exposure – Longer exposure to antimicrobial agents increases effectiveness.
- Microbial Characteristics – Some microbes (e.g., endospores, mycobacteria) are more resistant.
- Antimicrobial Agent Concentration – Higher concentrations usually enhance effectiveness.
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“Actions of Microbial Control Agents”
- Alteration of Membrane Permeability – Disrupts the cell membrane, causing leakage of essential intracellular substances.
- Damage to Proteins – Denatures enzymes and structural proteins, leading to loss of function.
- Damage to Nucleic Acids – Disrupts DNA and RNA, preventing replication and protein synthesis, ultimately killing the microbe.
What are the 3 Moist Heat Methods for Microbial Control?
- Boiling water
- Autoclave
- Steam contact
Kills most microbes but may not eliminate spores.
Boiling Water
Uses high-pressure steam to sterilize, ensuring complete microbial destruction.
Autoclave
Direct steam exposure is necessary for effective microbial killing.
Steam contact
____________ reduces spoilage organisms and
pathogens via heating.
Pasteurization
Some heat-resistant microbes (like thermophiles) may survive in Pasteurization.
Thermoduric Organisms
What are the 2 Methods of Pasteurization?
- High-Temperature Short-Time (HTST) – 72°C for 15 seconds, commonly used for milk.
- Ultra-High-Temperature (UHT) – 140°C for 3 seconds, sterilizes and extends shelf life.
“What are the 3 Methods of Dry Heat Sterilization?”
- Direct Flaming – Used for sterilizing inoculation loops in labs.
- Incineration – Burns and completely destroys contaminated materials.
- Hot-Air Sterilization – Uses dry heat at 160-170°C for 2-3 hours.
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“Physical Methods of Microbial Control”
- Filtration – Physically removes microbes from air or liquids.
- HEPA Filters (HIGH-EFFICIENCY PARTICULATE AIR) – Remove 99.97% of particles ≥ 0.3 microns, used in hospitals and clean rooms.
- Low Temperature – Slows microbial growth but doesn’t kill all microbes.
- Refrigeration – Slows down metabolism and reproduction.
- Deep Freezing – Preserves microbes but can kill some sensitive species.
- Desiccation – Removes water, preventing metabolism and growth (e.g., dried foods).
- Hypertonicity (Plasmolysis) – High salt or sugar concentrations cause water loss, shrinking the cell and inhibiting growth (e.g., salted meats, jams).
- Radiation – Damages DNA and other organic molecules, preventing microbial growth.
- Ionizing Radiation (X-rays, gamma rays, electron beams) – Produces reactive molecules that break DNA strands, used for sterilizing medical equipment and food.
- Non-ionizing Radiation (UV light) – Causes DNA mutations, effective for surface sterilization.
- Microwaves – Kill microbes indirectly by generating heat but are not highly antimicrobial.
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“Chemical Methods of Microbial Control”
Evaluating a Disinfectant: Use-Dilution Test
1️⃣ Inoculation – Stainless steel cylinders are coated with bacteria (Staphylococcus aureus, Salmonella choleraesuis, and Pseudomonas aeruginosa).
2️⃣ Drying – Cylinders are dried in an incubator to mimic real-world conditions.
3️⃣ Disinfection – Cylinders are placed in a test disinfectant for a set time.
4️⃣ Incubation – Cylinders are transferred to a broth medium to check for bacterial survival, determining the disinfectant’s effectiveness.
It is used to evaluate the effectiveness of antimicrobial agents.
Disk-diffusion method
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“Process of Disk-diffusion method”
1️⃣ Agar Plate Preparation – A petri dish is filled with agar and inoculated with the test microorganism.
2️⃣ Placement of Disks – Small filter paper disks soaked in different antimicrobial agents are placed on the agar surface.
3️⃣ Incubation – The plate is incubated to allow microbial growth and diffusion of the antimicrobial agents.
4️⃣ Zone of Inhibition – Clear zones around the disks indicate the effectiveness of the agents. Larger zones mean greater effectiveness.
Clear zones around the disks indicate the effectiveness of the agents. Larger zones mean greater effectiveness.
Zone of Inhibition
