26 Questions
What is the D value in sterilization?
Time to reduce the viable population by a factor of 10
What is the primary mechanism of heat killing in sterilization?
All of the above
What is the term for the time it takes to kill all cells at a given temperature?
Thermal death time
What is the purpose of sterility assurance?
To quantify the probability of item/area remaining unsterile
What is the difference between dry heat and moist heat in sterilization?
Moist heat is more effective, dry heat is less effective
What happens when condensation occurs onto cooler surfaces during heat sterilization?
Latent heat is released
Why is prior evacuation important before autoclaving?
To make the autoclaving process more effective
What is the primary purpose of sterilization and disinfection techniques?
To eliminate all microorganisms
What is the purpose of pasteurisation?
To destroy major pathogens and spoilage organisms
What is the purpose of using ionising radiation for sterilisation?
To sterilize medical equipment
What is the minimum temperature required for pasteurisation using the High Temperature Short Time (HTST) method?
72°C
Which microorganism is most resistant to gamma radiation?
E.Coli O157:H7
What is the purpose of autoclaving?
To destroy all microorganisms
Which of the following is NOT a type of radiation used for sterilisation?
Infrared radiation
What is a characteristic of autoclaving?
It is not suitable for all items
Which of the following microorganisms has the lowest resistance to gamma radiation?
Pseudomonas putida
What is the primary difference between bacteriostatic and bactericidal antibiotics?
Bacteriostatic antibiotics inhibit bacterial growth, while bactericidal antibiotics kill bacteria
What is the primary advantage of using chlorine-releasing agents as disinfectants?
They provide a high level of disinfection and are readily available
Which of the following antiseptics is known for its cationic surfactant properties?
Quaternary ammonium compounds
What is a characteristic of phenolic disinfectants?
They are stabilized by soaps or detergents
What is the primary difference between liquid chemicals and antiseptics?
Liquid chemicals are used for environmental disinfection, while antiseptics are used for skin disinfection
What is a characteristic of quaternary ammonium compounds?
They are cationic surfactants
What is the primary advantage of using chlorhexidine as an antiseptic?
It has a broad spectrum of activity and is well-tolerated by skin
What is the primary disadvantage of using chlorine-releasing agents as disinfectants?
They are corrosive to skin and metal instruments over time
What is the primary characteristic of bacteriolytic antibiotics?
They lyse bacterial cells
What is the primary advantage of using alcohols as antiseptics?
They are effective against a broad spectrum of microorganisms
Study Notes
Killing Kinetics
- D value: time required to reduce the viable population by a factor of 10 (time to kill 90%) under defined conditions
- D value is used to quantify the killing of microorganisms
Sterility Assurance
- Sterility assurance is the quantification of the probability of an item or area remaining unsterile despite undergoing a sterilization process
- Predicted probability of 10^(-6) is used as a sterility assurance standard for surgical instruments
Physical Control
Use of Heat
- Extremes of heat cause loss of structure and function to the fundamental macromolecules of bacterial cells (proteins, DNA, cell membrane)
- Thermal death time: the time it takes to kill all cells at a given temperature
- Optimum growth rate is between minimum and maximum temperatures
- Condensation onto cooler surfaces releases latent heat
- Dry heat vs Moist heat
- Most effective after prior evacuation (autoclave)
Antibiotics
- Major antibiotic families
- Specificity of action: broad spectrum vs narrow spectrum
- Bacteriostatic, bacteriocidal, and bacteriolytic effects
Disinfection Methods
Liquid Chemicals
- Chlorine-releasing agents:
- High level of disinfection (good activity spectrum)
- Examples: hypochlorite solutions, chlorinated isocyanurates
- Cheap and readily available
- Corrodes skin and metal instruments over time
- Reduced potency if organic debris present
- Quaternary ammonium compounds:
- Benzalkonium chloride (alkyl dimethyl benzyl ammonium)
- Cationic surfactant
- Lower toxicity at working concentrations
- Variable antiviral activity
- Applications: work surfaces, food preparation areas, preservations
- Phenolics:
- Solutions of mixed phenol-based compounds stabilized by soaps or detergents
- Synthetic phenolics (e.g. Dettol)
- Antiseptics:
- Alcohols
- Chlorhexidine
- Povidone Iodine
- Hydrogen peroxide
Autoclave
- Moist heat sterilization
- Sealed, evacuated chamber
- Application of steam heat under pressure (e.g. 121°C at 15psi) for 15-20 minutes
- Adequate to kill all microbes
Pasteurisation
- High Temperature Short Time (HTST): 72°C, 15 minutes
- Ultra High Temperature: 138°C, 2 minutes
- Adequate for destruction of major pathogens
- Adequate for destruction of spoilage organisms
- Preservation of flavor
- Does not eliminate ALL micro-organisms
Irradiation
- Non-ionizing: microwaves and UV
- Ionizing: X-rays and Gamma-rays
- UV radiation
- Radiation susceptibilities: D10 values (Grays, fresh food) for various microorganisms (e.g. Pseudomonas putida, Campylobacter jejuni, E. Coli O157:H7, Lactobacillus sp.)
This quiz is based on a microbiology lab experiment that involves counting viable organisms and observing their growth under different treatments. It tests your understanding of microbiological concepts and lab procedures.
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