Microbiology Sterilization Methods Quiz

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Questions and Answers

What is the primary method by which moist heat sterilization kills microorganisms?

By freezing their cellular structure

By coagulating their proteins (correct)

By dehydrating them

By disrupting their DNA

Which process effectively kills pathogens in milk but does not achieve complete sterilization?

Hot water bath at 60oC

Boiling at 100oC

Autoclaving at high pressure

Pasteurization at 63oC for 30 mins (correct)

What temperature is used in the special vaccine bath to inactivate non-sporing bacteria?

100oC for 15 minutes

70oC for 30 minutes

56oC for several days

60oC for 1 hour (correct)

What is the key invention made by Charles Chamberland in 1879 related to sterilization?

The autoclave Signup and view all the answers

What strong characteristic does boiling water have against bacterial pathogens?

It kills vegetative forms of bacterial pathogens Signup and view all the answers

What term describes the process that destroys all viable microorganisms?

Sterilization Signup and view all the answers

Which of the following agents inhibits the growth of bacteria without destroying them?

Bacteriostatic agent Signup and view all the answers

Which method is used to mechanically remove microbes from the skin surface?

Degermation Signup and view all the answers

What is the primary aim of sterilization in a medical context?

Eliminate all microorganisms Signup and view all the answers

Which of the following is NOT a characteristic of antiseptics?

Highly toxic materials Signup and view all the answers

What does the term sepsis refer to in a medical context?

Bacterial contamination Signup and view all the answers

What is the purpose of sanitization?

To cleanse and mechanically remove microbes Signup and view all the answers

Which of the following is true about sporicidal agents?

They kill endospores and not necessarily other pathogens Signup and view all the answers

What does the process of sterilization accomplish?

Removes all microorganisms including spores Signup and view all the answers

Which method is commonly used for sterilizing surgical instruments that cannot be exposed to moist heat?

Ethylene oxide gas Signup and view all the answers

What is a key difference between sterilization and disinfection?

Sterilization kills bacterial spores, disinfection does not Signup and view all the answers

What temperature and pressure is typical for the autoclaving process in sterilization?

121°C at 15 lb/in2 Signup and view all the answers

Which of the following methods is NOT classified under sterilization?

Application of antiseptic solutions Signup and view all the answers

What historical development greatly reduced nosocomial infections in surgeries?

Aseptic techniques developed by Lister Signup and view all the answers

Which statement best defines disinfection?

Kills many but not all microorganisms Signup and view all the answers

Which of the following methods is used for mechanical removal of microorganisms?

Filtration Signup and view all the answers

What is the primary effect of dry heat sterilization?

Kills by oxidation effects Signup and view all the answers

Which of the following is NOT a method of physical microbial control?

Antiseptics Signup and view all the answers

At what temperature and duration is dry heat sterilization most effective?

160°C for 2 hours Signup and view all the answers

What is a key characteristic of mechanical removal methods?

They involve the use of physical forces Signup and view all the answers

Which physical agent is considered non-ionizing radiation?

UV light Signup and view all the answers

What items can be sterilized using dry heat methods?

Metal instruments and oils Signup and view all the answers

What is the correct order of temperature and time for using an oven in dry heat sterilization?

160°C for 2 hours Signup and view all the answers

Which of the following methods is best suited for the destruction of contaminated materials?

Flaming/Incineration Signup and view all the answers

What is the primary action of hydrogen peroxide as an oxidizing agent?

Attacking sulfhydryl groups Signup and view all the answers

Which of the following materials can be sterilized using ethylene oxide?

Glass and metal Signup and view all the answers

What is a characteristic effect of metallic salts on microorganisms?

They act by coagulating proteins Signup and view all the answers

Which type of radiation is specifically used for sterilizing prepacked syringes and catheters?

Non-ionizing radiation Signup and view all the answers

What is the function of filtration in sterilization processes?

To remove bacteria from heat labile liquids Signup and view all the answers

At what temperature and duration is flash sterilization typically carried out?

132ºC for 3 minutes Signup and view all the answers

Which of the following chemical agents is effective against tubercle bacilli, fungi, and viruses?

Glutaraldehyde Signup and view all the answers

What is the primary mechanism of action for chemical agents in disinfection?

Protein coagulation and cell membrane disruption Signup and view all the answers

Which concentration range of alcohol is recommended for disinfection purposes?

60-90% Signup and view all the answers

What is the action of iodine as a disinfectant?

Bactericidal with moderate action against spores Signup and view all the answers

What type of materials can hydrogen peroxide be used to disinfect?

Contact lenses and wounds Signup and view all the answers

Formaldehyde is effective in preserving which of the following?

Anatomical specimens Signup and view all the answers

What is a limitation of the effectiveness of hydrogen peroxide as a disinfectant?

The organism's ability to produce catalase Signup and view all the answers

Study Notes

Sterilization, Disinfection, and Antisepsis

Microorganisms are agents of contamination, infection, and decay.
Early civilizations used methods like salting, smoking, pickling, and sunlight exposure to remove microorganisms.
In the mid-1800s, Lister developed aseptic techniques to prevent contamination of surgical wounds.
Nosocomial infections caused death in up to 10% of surgeries before aseptic techniques.
Up to 25% of mothers delivering in hospitals died due to infection before the development of aseptic techniques.

Learning Outcomes

Students should define sterilization, disinfection, and antisepsis.
Students should understand methods of sterilization and disinfection (physical, chemical, and mechanical removal).
Students should explain the role of sterilization and disinfection in disease control.

Introduction

Microorganisms are agents of contamination, infection, and decay.
Removing them from materials and areas is necessary.
Early civilizations used methods like salting, smoking, pickling, and sunlight exposure.

Aseptic Techniques

In the mid-1800s, Lister developed aseptic techniques to prevent contamination of surgical wounds.
Before this development, nosocomial infections caused death in 10% of surgeries, and up to 25% of mothers delivering in hospitals died due to infections.

Methods of Microbial Growth Control

Alteration of membrane permeability.
Damage to proteins.
Damage to nucleic acids.
Prions are the most resistant, followed by endospores of bacteria, mycobacteria, cysts of protozoa, vegetative protozoa, gram-negative bacteria, fungi (including most fungal spore forms), viruses without envelopes, gram-positive bacteria, and viruses with lipid envelopes, which are the least resistant.

Definition of Sterilization

Sterilization is the process of freeing an article from microorganisms, including their spores.

Sterilization

Sterilization is the killing or removal of all microorganisms, including bacterial spores, which are highly resistant.
Autoclaving (exposure to steam at 121°C under 15 lb/in² pressure for 15 minutes) is a common sterilization method.
Surgical instruments that can be damaged by moist heat are often sterilized by exposure to ethylene oxide gas.
Many intravenous solutions are sterilized by filtration.

Methods of Sterilization (Table 3-1)

Physical Sterilants: Steam under pressure (121°C or 132° C for various time intervals); Filtration (0.22–0.45-μm pore size, HEPA filters); Ultraviolet radiation (variable exposure to 254-nm wavelength); Ionizing radiation (variable exposure to microwave or gamma radiation)
Gas Vapor Sterilants: Ethylene oxide (450-1200 mg/L at 29°C to 65°C for 2-5 hr); Hydrogen peroxide vapor (30% at 55°C to 60°C); Plasma gas (highly ionized hydrogen peroxide gas)
Chemical Sterilants: Peracetic acid (0.2%); Glutaraldehyde (2%)

Disinfection

Disinfection is the killing of many, but not all, microorganisms.
For adequate disinfection, pathogens must be killed, but some organisms and bacterial spores may survive.
Disinfectants (corrosive phenol-containing, less toxic materials like ethanol and iodine) are used on non-living surfaces.
Antiseptics (chemicals used to kill microorganisms on the surface of skin and mucous membranes) are used on living surfaces.

Methods of Disinfection (Table 3-2)

Heat: Moist heat (75°C to 100°C for 30 min).
Liquid: Glutaraldehyde (2%–3.2%), Hydrogen peroxide (3%–25%), Chlorine compounds (100–1000 ppm free chlorine), Alcohol (70%–95%), Phenolic compounds (0.4%–5.0%), lodophor compounds (30–50 ppm free iodine/L), Quaternary ammonium compounds (0.4%–1.6%).

Terminology

Degermation: mechanically removing microbes from surfaces like skin.
Sepsis: bacterial contamination.
Asepsis: absence of significant contamination.
Bactericidal (microbicidal): agent that kills microbes.
Bacteriostatic (microbiostatic): agent that inhibits microbial growth but does not necessarily kill them.
Sporicidal: an agent that kills spores.

Sterilization and Asepsis

Asepsis is the practice to reduce or eliminate contaminants from entering an operative field (in surgery or medicine) to prevent infection.

Methods of Sterilization

Physical Agents: Heat (dry and moist), Radiation (non-ionizing and ionizing), Filtration.
Chemical Agents: Gases (ethylene oxide, hydrogen peroxide), Liquids (alcohols, phenols, aldehydes, chlorine, iodine, etc.)
Mechanical Removal Methods: Filtration (air and liquids).

Sterilization By Dry Heat

Kills by oxidation effects.
Uses dry heat to sterilize articles.
Operates between 50°C and 250/300°C.
Holding period of 160°C for 2 hrs is desirable.
Thermostat controls temperature.
Double-walled insulation keeps heat in and conserves energy.
Uses: sterilize forceps, scissors, scalpels, swabs, and pharmaceuticals.

Flaming/Incineration

An excellent method for destroying contaminated cloth, animal carcasses, and pathological materials.
For sterilizing inoculating loops, wires, tips of forceps, or spatulas.

Moist Heat Sterilization

Kills microorganisms by coagulating their proteins.
Methods:
- Temp below 100°C: “Pasteurization”, Inspissator.
- Temp at 100°C: Boiling.
- Steam at atmospheric pressure: Koch/Arnold’s steamer.
- Steam under pressure: Autoclave.

Pasteurization

Process of killing pathogens in milk without sterilizing it.
Milk is heated at 63°C for 30 minutes (Holder Method).
Or at 72°C for 15–20 seconds, rapidly cooled to 13°C (Flash Process).

Hot Water Bath

To inactivate non-sporing bacteria for vaccine preparation.
Special vaccine bath at 60°C for 1 hour.
Serum or body fluids with coagulable proteins can be sterilized by heating at 56°C for 1 hour in a water bath.

Temperature at 100°C

Boiling kills vegetative forms of bacterial pathogens.
Hepatitis virus survives up to 30 minutes of boiling.
Endospores can survive up to 20 hours or more of boiling.

Steam Under Pressure – Autoclave

Based on steam under pressure.
Invented by Charles Chamberland in 1879.

Autoclave

Consists of a vertical or horizontal cylinder.
One end is for placing materials to be sterilized.
Lid has a pressure gauge to measure pressure.
Safety valve allows for steam escape.
Sterilization is done at 121°C for 15 minutes, or 132°C for 3 minutes (flash sterilization).

Principles of Effective Disinfection (page 36)

Concentration of disinfectant
Organic matter
pH
Time

Alcohols

Ethanol/isopropyl alcohol are frequently used disinfectants.
Have no action on spores.
60-90% in water is commonly used concentration.
Uses include disinfection of clinical thermometers and skin (venipuncture).

Aldehydes

Formaldehyde and glutaraldehyde are frequently used.
Formaldehyde is bactericidal, sporicidal, and has a lethal effect on viruses.
Glutaraldehyde is effective against tubercle bacilli, fungi, and viruses.

Halogens

Iodine in aqueous and alcoholic solutions is widely used for skin disinfection.
Active, bactericidal, but moderate against spores.
Chlorine and its compounds are disinfectants in water supplies and swimming pools.

Phenols

Obtained by coal tar distillation.
Powerful microbicidal substances.
Derivatives like Lysol and cresol are widely used disinfectants in hospitals.

Hydrogen Peroxide

Used as an antiseptic to clean wounds and disinfect contact lenses, but its effectiveness is limited due to catalase enzyme.
An oxidizing agent that attacks sulfhydryl groups, inhibiting enzymatic activity.

Gases

Ethylene oxide is a colorless, sweet-smelling gas.
Effective against all microorganisms, including viruses and spores.
Used to sterilize heart-lung machines, respirators, sutures, dental equipment, books, clothing, and other surfaces.

Metallic Salts

Salts of silver, copper, and mercury are used as disinfectants.
Act by coagulating proteins, producing a bacteriostatic or bactericidal effect.
Have limited fungicidal activity.

Sterilization by filtration

Helps remove bacteria from heat-labile liquids (sera and antibiotic solutions).
Uses candle filters, asbestos filters, sintered glass filters, and membrane filters.

Radiation

Non-ionizing radiation (e.g., UV rays): Absorbed as heat; used for rapid mass sterilization of pre-packed syringes and catheters.
Ionizing radiation (e.g., X-rays, gamma rays): High penetrating power, no appreciable increase in temperature ("cold sterilization"); used to sterilize plastics, syringes, catheters, fabrics, and metal foils.

Ultrasonic and Sonic Vibration

Bactericidal but microorganisms vary in sensitivity.
Hence no practical value in sterilization and disinfection.

Germicidal Properties of Disinfectants and Antiseptics

A table that shows which disinfectants and antiseptics are effective against specific germicidal agents (bacteria, mycobacteria, bacterial spores, fungi, and viruses).

References

Various Microbiology books and websites are cited/referenced.

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Description

Test your knowledge on microbiology sterilization methods with this quiz. Explore various techniques, terms, and historical inventions related to microbial control. Understand key concepts such as hygienic practices and the differences between antiseptics and disinfectants.