Microbiology Lab Experiment

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Questions and Answers

What is the D value in sterilization?

Time to kill 99% of the viable population

Time to reduce the viable population by a factor of 10 (correct)

Time to kill 10% of the viable population

Time to kill 90% of the viable population

What is the primary mechanism of heat killing in sterilization?

Denaturation of proteins

Breakage of cell membrane

Disruption of DNA structure

All of the above (correct)

What is the term for the time it takes to kill all cells at a given temperature?

Thermal death rate

Sterilization time

Thermal death time (correct)

Killing kinetics

What is the purpose of sterility assurance?

To quantify the probability of item/area remaining unsterile Signup and view all the answers

What is the difference between dry heat and moist heat in sterilization?

Moist heat is more effective, dry heat is less effective Signup and view all the answers

What happens when condensation occurs onto cooler surfaces during heat sterilization?

Latent heat is released Signup and view all the answers

Why is prior evacuation important before autoclaving?

To make the autoclaving process more effective Signup and view all the answers

What is the primary purpose of sterilization and disinfection techniques?

To eliminate all microorganisms Signup and view all the answers

What is the purpose of pasteurisation?

To destroy major pathogens and spoilage organisms Signup and view all the answers

What is the purpose of using ionising radiation for sterilisation?

To sterilize medical equipment Signup and view all the answers

What is the minimum temperature required for pasteurisation using the High Temperature Short Time (HTST) method?

72°C Signup and view all the answers

Which microorganism is most resistant to gamma radiation?

E.Coli O157:H7 Signup and view all the answers

What is the purpose of autoclaving?

To destroy all microorganisms Signup and view all the answers

Which of the following is NOT a type of radiation used for sterilisation?

Infrared radiation Signup and view all the answers

What is a characteristic of autoclaving?

It is not suitable for all items Signup and view all the answers

Which of the following microorganisms has the lowest resistance to gamma radiation?

Pseudomonas putida Signup and view all the answers

What is the primary difference between bacteriostatic and bactericidal antibiotics?

Bacteriostatic antibiotics inhibit bacterial growth, while bactericidal antibiotics kill bacteria Signup and view all the answers

What is the primary advantage of using chlorine-releasing agents as disinfectants?

They provide a high level of disinfection and are readily available Signup and view all the answers

Which of the following antiseptics is known for its cationic surfactant properties?

Quaternary ammonium compounds Signup and view all the answers

What is a characteristic of phenolic disinfectants?

They are stabilized by soaps or detergents Signup and view all the answers

What is the primary difference between liquid chemicals and antiseptics?

Liquid chemicals are used for environmental disinfection, while antiseptics are used for skin disinfection Signup and view all the answers

What is a characteristic of quaternary ammonium compounds?

They are cationic surfactants Signup and view all the answers

What is the primary advantage of using chlorhexidine as an antiseptic?

It has a broad spectrum of activity and is well-tolerated by skin Signup and view all the answers

What is the primary disadvantage of using chlorine-releasing agents as disinfectants?

They are corrosive to skin and metal instruments over time Signup and view all the answers

What is the primary characteristic of bacteriolytic antibiotics?

They lyse bacterial cells Signup and view all the answers

What is the primary advantage of using alcohols as antiseptics?

They are effective against a broad spectrum of microorganisms Signup and view all the answers

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.)

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Description

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.