Control of Microorganism and Sterilisation and Disinfection Flashcards by Steven Head

What is the purpose of the control of microorganisms

To remove microorganisms to prevent spoilage and infection

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What are the ways in which we prevent spoilage?

Smoking
Salting
Drying in sunlight
Pickling
Fruit jam/preserves
Pasteurisation

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What is Louis Pasteur known for?

Proposed the germ theory of disease

Discovered that heating food and beverages prevented spoilage

Patented the technique ‘pasteurisation’

Disproved the theory of spontaneous generation

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What is Joseph Lister known for?

Prior to Lister people believed that infection was due to ‘bad air’ or miasma

Surgeons of the day thought there dirty blood stained gowns demonstrated their experience

Inspired by Pasteur he demonstrated treating surgical instruments with 5% carbolic acid reduced infections

Promoted clean gloves and washing hands

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Define cleaning

It is a process which removes visible contamination but does not necessarily destroy microorganisms. It is a necessary prerequisite for effective disinfection or sterilisation

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Define Disinfection

Is a process which reduces the number of viable microorganisms to an acceptable level but may not inactive some viruses, bacterial spores and prions.

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Define Sterilisation

Is the process of destruction or removal of all microorganisms from article, surface or medium, including bacterial spores.

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What is the difference between Physical and chemical?

Physical control includes heat, irradiation, filtration and mechanical removal

Chemical control involves the use of antimicrobial chemicals

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(Factors influence the effectiveness of antimicrobial treatment) How does the number of Microbes effect this?

The more microbes present, the more time it takes to eliminate population

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(Factors influence the effectiveness of antimicrobial treatment) How does the type of Microbes effect this?

Endospores are very difficult to destroy.

Vegetative pathogens vary widely in susceptibility to different methods of microbial control

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(Factors influence the effectiveness of antimicrobial treatment) How do Environmental influences affect this?

Presence of organic material (blood, faeces, saliva, pH etc.)

Tends to inhibit antimicrobials

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(Factors influence the effectiveness of antimicrobial treatment) How does the Time of exposure affect his?

Chemical antimicrobials and radiation treatments are more effective at longer times.

In heat treatments, longer exposure compensates for lower temperatures

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(Rate of Microbial death) Explain Death rate

When bacterial populations are heated or treated with antimicrobial chemicals

They usually die at a constant rate

Kill kinetics

We can then determine the required exposure time

To achieve complete inactivation

This can be confirmed by culture

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(Physical Methods) Explain Heat method

Kills microorganisms by denaturing their enzymes and other proteins. Heat resistance varies widely among microbes.

Fast, reliable, inexpensive

Does not introduce potential toxic substances

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What are the types of heat control?

Dry heat

Moist heat

Pasteurization

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(Dry Heat) Explain Flaming

Inoculation loop

Held in a Bunsen flame till they are red hot

This will kill the microorganisms

The loop can then be used to ‘streak’ out a patients sample to get single colonies

I now use disposable plastic loops

(Dry Heat) What is Hot air Oven used for?

Used to sterilise items that do not become damaged by high temperatures

Lab glassware (Bottles, measuring cylinders and metal tools)

(Dry Heat) How does the Hot Air Oven work?

Operated between 50°C to 300°C.

A holding period of 160°C for 1 hr is desirable.

There is a thermostat controlling the temperature.

Double-walled insulation keeps the heat in and conserves energy

Also used to dry things sterilised by moist heat

(Dry Heat) What are the Advantages and Disadvantages of Hot Air Ovens?

Advantages

Can be used for powders, anhydrous oils

Inexpensive

No corrosive effect on instruments

Disadvantages

High temperature damages some items

Penetration of heat slow, uneven

(Dry Heat) What is Incineration used for?

Used to sterilise and destroy clinical waste

Patient samples

Tissue

Microorganisms

Sharps

Contaminated textiles

Laboratory plasticware

Animal carcasses

Define the role of Moist Heat

Kills microorganisms by coagulating their proteins

(Moist Heat) Explain the process of Boiling

Heat to 100oC or more at sea level

Kills vegetative forms of bacterial pathogens

Most pathogens can be killed within 10 minutes or less

Endospores and some viruses are not destroyed this quickly

What does Moist Heat require?

Reliable sterilisation with moist heat requires temperatures above that of boiling water.

(Moist Heat) How does an AutoClave work?

Chamber which is filled with hot steam under pressure

Preferred method of sterilisation, unless the material is damaged by heat, moisture, or high pressure

The temperature of steam reaches 121oC at twice atmospheric pressure

All organisms and endospores are killed within 15 minutes

What is the Role of Filtration?

Removal of microbes by the passage of a liquid or gas through a screen like material with small pores Used to sterilise heat sensitive materials like vaccines, enzymes, antibiotics, and some culture media

(Filtration) What are Membrane Filters?

Uniform pore size Used in industry and research. Different sizes: 0.22 and 0.45μm Pores Used to filter most bacteria. Don’t retain spirochetes, mycoplasmas and viruses

What is the Role of Chemical cleaning?

The mechanism of action of most of the chemicals are nonspecific and complex but most of them effect microorganisms by one of the following mechanisms Cell membrane injury Coagulation and Denaturation Interactions with functional groups of proteins

What the chemical cleaning method used for in labs?

Sterilise surfaces Clean up spills Inactivate organisms in solutions

Explain Hydrogen Peroxide in the use of Contact lens Hygiene (H2O2)

Strong oxidant Oxidisingproperties allow it to destroy wide range of pathogens Used at 3% in contact lens disinfectants Uses a platinum disk or catalase tablet to neutraliseperoxide Risk of burning eyes Can be used in 30% concentration to clean surfaces

What single-use items are used in a lab?

Petri dishes Centrifuge tubes Tissue culture flask Filters Syringes 96 well plates Pasteur pipettes / Stripettes

Ionising Radiation, how is this involved with cleaning?

Items are prepared in clean room environments Irradiated with gamma rays Gamma rays destroy the DNA of any organism present Excellent penetration Rapid method of cold sterilisation

How is Peroxide used as a chemical disinfectant?

Hydrogen peroxide is a widely used antimicrobial chemical. It is used in both liquid and gas form for preservative, disinfection and sterilization applications. However, overall, the effective and safe use of hydrogen peroxide depends on the way it is used, in particular, the concentration.

How are Biguanides used as a chemical disinfectant?

The in-use solution is stable but is affected by organic soil and, to some extent, by hard water. Most biguanides have equal antibacterial activity against Gram-positive and Gram-negative microorganisms. They are less effective against moulds and yeasts and are ineffective against bacterial spores and viruses.

How is QAT's used as a chemical Disinfectant?

QAT's (or Quats) is the most widely used biocides in food or beverage businesses. Properly formulated products are effective against gram-positive bacteria and against gram-negative bacteria, but less effective against spores, moulds and fungi. QAT based disinfectants are stable and generally taint free