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Microbial Sterilization and Disinfection
10
Transcript
Microbial Sterilization and Disinfection
Introduction
About
- The scientific concept of microbial growth began 100 years ago when Ignatz Semmelweis and Joseph Lister introduced methods such as:
- - handwashing with disinfectants
- - boiling instruments
- This lowered the infection rate in hospitals
Definitions
Mission
- Sterilization
- - Killing/ removal of all microbes (including endospores)
- - Is absolute
- - EG: Heat, radiation, chemical agents
- Disinfection
- - Killing of many but not all micro-organisms
- - For adequate disinfection, pathogens must be killed
- - Disinfection refers to chemical applied to an object
Person Profiles
Action of Anti-Microbials Agents
- Anti - microbial agents vary in their ability to kill microbes.
- - Some have more than 1 mechanism of action but few can achieve complete sterility
- Anti - microbial agents act by:
- - Alteration of Membrane Permeability
- > Attack the cell wall: Increases cell permeability
- - Damage to Proteins, Nucleic Acids
Anti-Microbial Agents
Chemical Agents
- Chemical agents are used to control the growth of microbes on living tissues and inanimate objects.
- There is no one disinfectant that will be appropriate for all circumstances
Phenol
- Originally used by Joseph Lister in the operating theatre
- Rarely used nowadays as it has a disagreeable odor and it irritates the skin
- - Causes skin ulcers
- Mechanism of action is through damaging the microbe's cell membrane as well as denaturing proteins
- Not sporicidal
Phenolic Derivatives
- Not sporicidal
1. Cresol
- Good surface disinfectant: floors
- Used in Lysol
2. Hexachlorophene
- Soaps, lotions (pHisohex)
- Effective against Staph, Strep
- Excessive use can cause neurological damage
Chlorhexidine
Chlorhexidine
- Combined with a detergent or alcohol for surgical scrubs and preoperative skin preparations
- More rapid onset of action compared to hexachlorophene
- Killing effect is related to its damage to the plasma membrane
- Effective against most bacteria but is not sporicidal
- - No toxic effect
Alcohol
Key
Projects
- Widely used to clean skin
- Acts and evaporates rapidly; leaves no residue
- Kills bacteria, fungi but not naked viruses
- Disrupts cell membrane by dissolving lipid component, denatures proteins
- Unsatisfactory when applied to wounds as they cause coagulation of a layer of protein under which bacteria continue to grow
- EG: Ethanol, isopropanol
Surface-Active Agents
- Divided into:
- - Soaps
- - Quartenary Ammonian Compounds
Project 1
Quaternary Ammonium Compounds
Quaternary Ammonium Compounds
- Have a positive portion which interacts with the cell membrane
- Affect permeability and cause loss of electrolytes
- Bactericidal against Gram positive bacteria
- Do not kill endospores
- Certain bacteria can survive and grow in them
- - EG: Pseudomonas
- Examples: Cepacol
Halogens
Project 2
Are effective against microbes
1. Chlorine
- Used to purify water, treat swimming pools
- Strong oxidising agent that inactivates enzymes: very irritant
- EG: Hypochlorite in Chlorox
2. Iodine
- One of the oldest and most effective antiseptic
- Inactivates enzymes, proteins
Compounds of Iodine
Compounds of Iodine
- Tincture
- - Solution of iodine with alcohol
- - Used to prepare skin before blood culture
- - Disadvantage is that it stains, irritates the skin
- Iodophor
- - Complex of iodine with detergents
- - Less irritating and do not stain
- - Pseudomonas can survive in it
- - EG: Betadine, Isodine
Aldehydes
Project 3
- Among the most effective anti-microbial
Formaldehyde
Formaldehyde
- Available as formalin
- Carcinogenic
- Used to preserve tissue specimens
- Strong irritant to eye and skin
Glutaraldehyde
Glutaraldehyde
- 10times more effective than formaldehyde
- Less toxic
- Example: Cidex
- - Used to sterilize respiratory theraphy equipment
Physical Agents
Heat, Filtration and Radiation
Stats
Heat
- Most common method by which microbes are killed
- EG: Canning of food
- Economical and easy to control
- Kills microbes by denaturing their enzymes
a. Moist Heat
a. Moist Heat
Boiling
- 100 degree Celcius kills most pathogens in 10mins
- Steam also effective
- Some viruses, endospores not destroyed
Autoclaving
- Most frequently used method in clinics
- Steam under pressure
- - 121 degree Celcius for 15mins
- Most effective when microbes in direct contact with steam
- Kills all organism and endospores
b. Dry Heat
b. Dry Heat
Direct Flaming
- Simplest method
Hot Air Sterilization in Oven
- Requires temperature of 180 degree Celcius for 2h
- Used to sterilize glassware
c. Pasteurization
c. Pasteurization
- Used mainly for milk
- Heating milk to 62 degree Celcius for 30mins, followed by rapid cooling
- Kills most milk-borne pathogens
- Keeps refrigerated for serveral days
Filtration
Filtration
- Is the passage of a liquid or gas through porous material to trap particles larger than the pore size
- Used to sterilize heat-sensitive materials
- EG: Culture media, enzymes, vaccine
- Latest filters can retain viruses
- - 0.01 micrometres pore
Radiation
Radiation
- EG: X-ray, Gamma ray, UV ray
- Used to sterilize heat-sensitive materials
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