Microbial Control and Sterilization Techniques

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Questions and Answers

What is the primary purpose of sterilization?

To reduce the number of microorganisms

To prevent the spread of infections

To kill all microorganisms including spores (correct)

To clean surfaces from visible dirt

What is a common method of sterilization for materials that cannot tolerate moist heat?

Filtration

Ethylene oxide gas exposure (correct)

Autoclaving

Chlorination

How did Aseptic techniques impact surgery in the 1800s?

Reduced nosocomial infections post-surgery (correct)

Increased the risk of infections

Eliminated all types of surgeries

Had no significant effect on mortality rates

Which of the following best defines disinfection?

Killing of many but not all microorganisms Signup and view all the answers

What role do antiseptics play in microbial control?

Kill pathogens on surfaces of skin and mucous membranes Signup and view all the answers

What is the primary use of beta propiolactone (BPL)?

Fumigation for sterilization Signup and view all the answers

Which filter is known for its high adsorbing tendency but also has carcinogenic properties?

Asbestos filter Signup and view all the answers

Which type of filter is prepared by heat fusing powdered glass particles and is known for being brittle and expensive?

Sintered glass filter Signup and view all the answers

What is the function of membrane filters?

For sterilization and sterility testing Signup and view all the answers

Which type of candle filter is specifically mentioned as a Chamberland filter?

Unglazed ceramic filter Signup and view all the answers

What is the purpose of the pressure gauge in an autoclave?

To measure the pressure within the sterilization chamber Signup and view all the answers

What is the required exposure time and temperature for sterilization using an autoclave?

15 minutes at 121 °C Signup and view all the answers

Which type of radiation is used for the rapid mass sterilization of prepacked syringes?

Non-ionising radiation Signup and view all the answers

Tyndallisation is used for media containing sugar and gelatin. What is the exposure condition for this process?

100 °C for 20 minutes for 3 successive days Signup and view all the answers

Who invented the autoclave and in what year?

Charles Chamberland in 1879 Signup and view all the answers

Which group of dyes is effective against Gram positive bacteria?

Aniline dyes Signup and view all the answers

What is one of the important dyes in the acridine dye category?

Proflavine Signup and view all the answers

Which disinfectant is known for being bactericidal and having moderate activity against spores?

Iodine Signup and view all the answers

What is the primary purpose of a hot air oven in sterilization?

To sterilize articles through dry heat Signup and view all the answers

What substance is effective as an antiseptic to clean wounds but is limited by the organism's ability to produce catalase?

Hydrogen peroxide Signup and view all the answers

Which temperature range is typical for the operation of a hot air oven?

50 to 250/300°C Signup and view all the answers

What is the primary use of ethylene oxide?

Sterilization of various equipment Signup and view all the answers

Which of the following is not a characteristic of phenolic compounds?

Commonly found in aqueous solutions Signup and view all the answers

What article is NOT typically sterilized using a hot air oven?

Biological waste Signup and view all the answers

What is a key advantage of double-walled insulation in a hot air oven?

Conserves energy by retaining heat Signup and view all the answers

Which uses hydrogen peroxide as an antiseptic?

Cleaning wounds and disinfecting contact lenses Signup and view all the answers

How does flaming sterilize instruments such as an inoculation loop?

By heating them until they are red hot 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

What does the term 'mechanical removal methods' refer to in microbial control?

Filtration of air and liquids Signup and view all the answers

Which method is primarily used for sterilization of air?

UV radiation exposure Signup and view all the answers

What is the function of a thermostat in a hot air oven?

Maintains the temperature within a set range Signup and view all the answers

What is the purpose of incineration in waste management?

Destroying contaminated materials Signup and view all the answers

Which of the following temperatures is used for pasteurization using the Holder method?

63oC for 30 minutes Signup and view all the answers

What type of materials is sterilized using an inspissator?

Lowenstein-Jensen media Signup and view all the answers

Which of the following methods is effective for killing vegetative bacterial pathogens in liquids?

Boiling at 100oC Signup and view all the answers

What is the main function of the steam generated in a Koch/Arnold's steamer?

To surround materials with steam for sterilization Signup and view all the answers

In a hot water bath, what is the typical temperature used for inactivating non-sporing bacteria for vaccine preparation?

60oC for 1 hour Signup and view all the answers

Which method utilizes steam under pressure for sterilization?

Autoclave Signup and view all the answers

What happens to endospores during boiling at 100oC?

They can survive for hours Signup and view all the answers

Study Notes

Sterilization, Disinfection, and Antiseptic

Microorganisms cause contamination, infection, and decay.
Early civilizations used methods like salting, smoking, pickling, and sunlight exposure to preserve food.
Aseptic techniques were developed in the mid-1800s to prevent contamination of surgical wounds.
Prior to this, nosocomial infections caused high death rates during surgeries.
Up to 25% of mothers delivering in hospitals died from infections.

Methods of Microbial Growth Control

Microbes vary in resistance to control methods.
Methods alter membrane permeability, damage proteins, and damage nucleic acids.
Prions are most resistant, followed by endospores, mycobacteria, cysts of protozoa, vegetative protozoa, Gram-negative bacteria, fungi, Gram-positive bacteria, viruses without envelopes, and lastly viruses with lipid envelopes.

Definition of Sterilization

Sterilization removes all microorganisms, including spores.
Sterilization is a critical process before surgery.

Methods of Sterilization

Methods include autoclaving (steam at 121°C under pressure for 15 mins), ethylene oxide gas, and filtration.
Surgical instruments that can't withstand moist heat are sterilized by ethylene oxide or sometimes filtration.
Intravenous solutions are often sterilized through filtration.

Disinfection

Disinfection kills many microorganisms, but not all.
Chemicals used to kill microorganisms on skin and mucous membranes are antiseptics.

Terminology

Sterilization destroys all viable microbes, including viruses and endospores.
Disinfection destroys vegetative pathogens, but not endospores, on inanimate objects.
Antiseptics are disinfectants used on exposed body surfaces.
Sanitization is any cleansing method that mechanically removes microbes.
Degermation is the mechanical removal of microbes from surfaces.
Asepsis is the absence of significant contamination.
Bactericidal (microbicidal) means the agent kills.
Bacteriostatic (microbiostatic) means the agent inhibits growth.

Bacteriostatic Agent

An agent that inhibits bacterial growth but does not necessarily kill them.

Bactericide

An agent that kills bacteria.
Most do not kill endospores.

Sporicide

An agent that kills spores.

Aim of Sterilization

Asepsis reduces/eliminates contaminants like bacteria, viruses, fungi, and parasites to prevent infection.
An ideal sterile environment is free of contaminants, but difficult to attain practically.
The goal is to eliminate infection, not complete sterility.

Methods of Sterilization (Chart)

Methods include physical, chemical, and mechanical.

Physical Sterilization Methods (Chart)

Methods include heat (dry and moist), radiation (ionizing and non-ionizing), and incineration.

Physical Sterilization Methods: Methods (Heat)

Sterilization in dry ovens heats and kills the pathogens.
Sterilization using boiling water/hot water/pasteurization.

Chemical Methods

Gasses like ethylene oxide
Liquids like chemotherapy and antiseptics

Mechanical Methods

Methods like filtration

Examples of Methods of Sterilization (Further Detail)

Hot Air Oven: Kills microorganisms by oxidizing effects using dry heat between 50°C to 250/300°C. A holding period of 160°C for 1 hour is desirable. Double walled insulation helps conserve energy.
Flaming: Involves directly exposing articles (e.g., inoculation loop, wire, forceps, spatulas) to a Bunsen burner flame until they are red-hot to kill microorganisms.
Incineration: Excellent method to destroy contaminated materials (e.g., cloth, animal carcasses, pathological materials).
Moist Heat Sterilization: Kills microorganisms by coagulating their proteins.

Moist Heat Sterilization Methods

Methods of sterilization using moist heat include temperature below 100°C like pasteurization/inspissator, and 100°C like boiling.
Moist heat methods also include using steam at atmospheric pressure, as in Koch/Arnold's steamer, and steam under pressure using the autoclave.

Sterilization Using Certain Methods (Further Detail)

Pasteurization: Kills pathogens in milk without sterilizing, using the holder method at 63°C for 30 minutes, or the flash process at 72°C for 15–20 seconds with rapid cooling to 13°C.
Water Baths: Used for the inactivation of non-spore forming bacteria typically with 60°C for one hour.
Inspissator: Sterilization by heating at 80–85°C for half an hour for three successive days. Often used as a sterilizing media that contain substances like sugar and gelatin.

Boiling

Kills vegetative forms of bacterial pathogens, but some viruses can survive up to 30 minutes of boiling. Endospores can withstand up to 20 hours of boiling.

Steam Sterilizer

Steam is generated to sterilize materials through the use of a steamer (Koch/Arnold), having a tin cabinet and conical lid to drain condensed steam.
Perforated tray allows for the steam to surround the materials for 90 mins. A typical usage time.
Tyndallisation /Intermittent Sterilization: Used for materials that contain sugar and gelatin with 100°C exposure for 20 mins for three successive days.

Steam Under Pressure - Autoclave

Works on the principle of steam under pressure.
Invented by Charles Chamberland in 1879.
Autoclave consists of a vertical/horizontal cylinder and an opening for material insertion.
Lid provided with pressure gauge to measure pressure,
Safety valve present for steam escape.

Radiation

Two types: ionizing and non-ionizing.

Non-Ionizing Radiation

Electromagnetic rays with longer wavelengths, absorbed as heat.
Used in rapid mass sterilization (e.g., UV rays) of syringes and catheters; sometimes hot air sterilization.

Ionizing Radiation

X-rays, gamma rays, cosmic rays.
High penetrative power without considerable temperature increase.
Used to sterilize plastics, syringes, catheters, or grease fabrics, metal foils.

Ultrasonic and Sonic Vibration

Bactericidal, but microbes vary in sensitivity.
Not a practical sterilization/disinfection method due to varied microbe sensitivity.

Chemical Agents

Act by proteins coagulation, disrupting cell membranes, removing sulfhydryl groups, or by substrate competition.

Principles of Effective Disinfection

Concentration of disinfectant, organic matter removal, pH, and time are key factors.
70-90% concentration of commonly used sanitizers, organic matter that needs to be removed.

Alcohols

Ethanol/Isopropyl alcohol frequently used as disinfectants (not for spores).
60-90% concentration in water is recommended.
用于消毒体温计及皮肤（如静脉穿刺前）。

Aldehydes

Formaldehyde & Glutaraldehyde used; formaldehyde is bactericidal, sporicidal, and lethal to viruses.
Glutaraldehyde is effective against tuberculosis bacilli, fungi, and viruses.

Dyes

Two groups: aniline dyes (brilliant green, malachite green, crystal violet) - often effective against Gram-positive bacteria; acridine dyes (orange-coloured dyes like proflavine, acriflavine, euflavine) - often more effective against Gram-positive than Gram-negative bacteria.

Halogens

Iodine in aqueous/alcoholic solutions is used as a skin disinfectant; moderately effective against spores.
Chlorine compounds are used as disinfectants in water supplies and swimming pools.

Phenols

Obtained by coal tar distillation.
Phenols/phenolic derivatives widely used as disinfectants in hospitals (e.g., lysol, cresol, Detol).
Various combinations used in surgical/neonatal units and wound treatment.

Hydrogen Peroxide

Used as an antiseptic to clean wounds and disinfect contact lenses.
Effectiveness limited by the presence of catalase, an enzyme that degrades H₂O₂ by releasing oxygen.

Gases

Ethylene Oxide: Colorless gas with a sweet ethereal smell; effective against all microbes (including viruses and spores).
Used in sterilizing heart-lung machines, respirators, sutures, dental instruments, books, clothing, glass, metal, paper, plastics, oil, some foods, and tobacco.
Formaldehyde gas is frequently employed in fumigation of operating rooms and other spaces.
Beta Propiolactone: Used in fumigation for sterilization. Rapidly biocidal, very effective against viruses.

Sterilization by Filtration

Removes bacteria from heat-labile liquids (e.g., serum, antibiotics).
Utilizes filters like candle filters, asbestos filters, sintered glass filters, and membrane filters.

Candle Filters

Unglazed ceramic filters (Chamberland) or diatomaceous earth filters (Berkefeld).

Asbestos Filters

Disposable single-use discs with high adsorbing tendency; potential carcinogen (e.g., Seitz filter).

Sintered Glass Filters

Prepared by fusing powdered glass particles of graded sizes. Cleaned easily; brittle and expensive.

Membrane Filters

Made from cellulose esters or other polymers; used for water purification, sterilization, and sterility testing in preparing solutions for parenteral use.

References

Principles and Methods of Sterilization in Health Sciences (2nd ed. by John J. Perkins).
Jawetz Melnick & Adelbergs Medical Microbiology.
Review of Medical Microbiology and Immunology (14th ed. by Warren Levinson, MD, PhD).

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Test your knowledge on sterilization methods and microbial control techniques with this quiz. Explore the historical impact of aseptic techniques, the function of various filters, and the role of heat and radiation in sterilization processes. Perfect for students in microbiology and related fields.