Microbiology: Sterilization and Disinfection

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Questions and Answers

What method is used to sterilize inoculating loops and needles?

Direct Flaming

What is the purpose of pasteurization?

To prevent the spoilage of beverages

What is the minimum temperature required for hot air sterilization?

170oC

What is the difference between dry heat and moist heat?

Dry heat transfers heat less effectively to a cool body, than moist heat Signup and view all the answers

What is the purpose of incineration?

To sterilize disposable items and biological waste Signup and view all the answers

What is the minimum time required for hot air sterilization?

2 hours Signup and view all the answers

What are the two main categories of methods used to control microbial growth?

Physical methods and Chemical methods Signup and view all the answers

What is the pattern of microbial death when bacterial populations are heated or treated with antimicrobial chemicals?

A constant percentage of the extant population is killed each minute. Signup and view all the answers

What are the ideal characteristics of a sterilization/disinfection process?

Highly efficacious, Fast, Good penetrability, Compatible with all materials, Non-toxic, Effective despite presence of organic material, Difficult to make significant mistakes in process, Easily monitored Signup and view all the answers

What is an example of a physical method used to sterilize materials?

Dry heat or Moist heat Signup and view all the answers

What is the purpose of inoculating wires and loops with red heat?

To sterilize them Signup and view all the answers

What are the two methods of pasteurization mentioned in the text?

The two methods are Classic Method and High Temperature Short Time Pasteurization (HTST). Signup and view all the answers

What is an example of a chemical method used to disinfect surfaces?

Alcohols Signup and view all the answers

What is the purpose of using a fan in dry-heat sterilization?

To obtain uniform temperature by circulation. Signup and view all the answers

What is the temperature and duration required for HTST pasteurization?

72°C for 15 seconds. Signup and view all the answers

What is the purpose of Inspissation in sterilization?

To sterilize serum or egg media. Signup and view all the answers

How does dry heat kill microorganisms?

By denaturation of bacterial proteins, oxidative damage, and toxic effect of elevated levels of electrolytes. Signup and view all the answers

What are the factors that influence the effectiveness of heat in sterilization?

The factors are nature of heat, temperature and duration, characteristic of organism and spores, and type of material. Signup and view all the answers

What is the temperature and duration of steam used in Tyndallisation?

100°C for 20 minutes on three successive days Signup and view all the answers

What is the advantage of using steam above 100°C in an autoclave?

It has a better killing power than dry heat and bacteria are more susceptible to moist heat. Signup and view all the answers

What are the components of an autoclave?

A vertical or horizontal cylinder, lid with screw clamps, asbestos washer, discharge tap, pressure gauge, and safety valve. Signup and view all the answers

What are the standard sterilization conditions in an autoclave?

121°C, 15 lb per square inch, and 15 minutes holding time. Signup and view all the answers

What is the purpose of the discharge tap in an autoclave?

To release air and steam. Signup and view all the answers

Why are instruments packed for sterilization?

To be stored and handled without being contaminated. Signup and view all the answers

What pore size is required for filtration if viruses must also be removed?

around 20 nm Signup and view all the answers

How must filtration equipment and filters be sterilized?

by autoclaving at a temperature that does not damage the fragile filter membranes Signup and view all the answers

Why are prions not removed by filtration?

Not specified in the text, but prions are notoriously difficult to remove or inactivate. Signup and view all the answers

What type of air filtration is used in pharmaceutical sterile filtration?

HEPA (High Efficiency Particulate Air) filtration Signup and view all the answers

What additional method is often used in conjunction with HEPA filtration to kill trapped bacteria and viruses?

high-energy ultraviolet light units Signup and view all the answers

What is the purpose of testing the filtration system?

to ensure that the membranes have not been punctured prior to or during use Signup and view all the answers

Study Notes

Methods of Microbial Control

Various methods employed for microbial control include physical and chemical methods.

Physical Methods

Dry Heat Sterilization:
- Direct Flaming sterilizes inoculating loops and needles until they glow red.
- Incineration is used for sterilizing disposable items and biological waste.
- Hot Air Sterilization requires 2 hours at 170°C for effective sterilization, as dry heat transfers heat less effectively than moist heat.
Moist Heat:
- Pasteurization, developed by Louis Pasteur, prevents the spoilage of beverages like milk, yogurt, and juices by reducing microbes but does not eliminate all (heat-tolerant organisms may survive).
- Batch, flash, and ultrahigh-temperature methods are used for milk pasteurization.
Tyndallisation involves heating media (like serum and sugar) by exposing it to steam at 100°C for 20 minutes over three consecutive days.
Physical Filtration and Radiation:
- Filtration uses specialized filters (such as membrane filters) to separate microbes from liquids or gases.
Sunlight acts as a natural sterilization method due to its ultraviolet rays, effectively purifying water in natural sources.

Ideal Sterilization Process

Effective sterilization methods are characterized by rapid action, good penetrability, compatibility with materials, non-toxicity, resilience to organic material interference, and ease of monitoring.

Rate of Microbial Death

Bacterial populations die at a constant rate when subjected to heat or antimicrobial treatment; a constant percentage of microbes is killed over time.

Components of Autoclave

An autoclave consists of a steel cylinder that maintains high temperature and pressure—typically 121°C and 15 psi for 15 minutes, with variations such as 126°C for 10 minutes and 133°C for 3 minutes.

Packing for Sterilization

Instruments are packed to prevent contamination post-sterilization; filtration systems must ensure that membranes are intact to maintain sterility and prevent pathogenic spread.

Heat as a Microbial Killer

Heat effectively kills a majority of microbes; dry heat destroys organisms through denaturation of proteins and oxidative damage.

Sterilization Methods Summary

Common sterilization methods include:
- Red heat for inoculating wires and loops.
- Classic pasteurization involves heating milk to 65°C for 30 minutes.
- High-Temperature Short Time (HTST) pasteurization heats milk to 72°C for 15 seconds.

Factors Influencing Heat Efficacy

Parameters affecting heat’s effectiveness include:
- Nature and type of heat applied.
- Duration and temperature of exposure.
- Characteristics of the target organisms and materials involved.

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Description

Learn about the ideal sterilization and disinfection process, its characteristics, and the rate of microbial death. Understand the importance of sterilization and disinfection in controlling microbial growth.