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Microbiology and immunology > Control of Microorganism and Sterilisation and Disinfection > Flashcards

Control of Microorganism and Sterilisation and Disinfection Flashcards

1
Q

What is the purpose of the control of microorganisms

A

To remove microorganisms to prevent spoilage and infection

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2
Q

What are the ways in which we prevent spoilage?

A 
Smoking
Salting
Drying in sunlight
Pickling
Fruit jam/preserves
Pasteurisation
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3
Q

What is Louis Pasteur known for?

A

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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4
Q

What is Joseph Lister known for?

A

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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5
Q

Define cleaning

A

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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6
Q

Define Disinfection

A

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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7
Q

Define Sterilisation

A

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

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8
Q

What is the difference between Physical and chemical?

A

Physical control includes heat, irradiation, filtration and mechanical removal

Chemical control involves the use of antimicrobial chemicals

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9
Q

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

A

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

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10
Q

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

A

Endospores are very difficult to destroy.

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

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11
Q

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

A

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

Tends to inhibit antimicrobials

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12
Q

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

A

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

In heat treatments, longer exposure compensates for lower temperatures

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13
Q

(Rate of Microbial death) Explain Death rate

A

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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14
Q

(Physical Methods) Explain Heat method

A

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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15
Q

What are the types of heat control?

A

Dry heat

Moist heat

Pasteurization

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16
Q

(Dry Heat) Explain Flaming

A

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

17
Q

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

A

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

Lab glassware (Bottles, measuring cylinders and metal tools)

18
Q

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

A

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

19
Q

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

A

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

20
Q

(Dry Heat) What is Incineration used for?

A

Used to sterilise and destroy clinical waste

Patient samples

Tissue

Microorganisms

Sharps

Contaminated textiles

Laboratory plasticware

Animal carcasses

21
Q

Define the role of Moist Heat

A

Kills microorganisms by coagulating their proteins

22
Q

(Moist Heat) Explain the process of Boiling

A

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

23
Q

What does Moist Heat require?

A

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

24
Q

(Moist Heat) How does an AutoClave work?

A

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

25
Q

What is the Role of Filtration?

A

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

26
Q

(Filtration) What are Membrane Filters?

A

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

27
Q

What is the Role of Chemical cleaning?

A

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

28
Q

What the chemical cleaning method used for in labs?

A

Sterilise surfaces

Clean up spills

Inactivate organisms in solutions

29
Q

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

A

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

30
Q

What single-use items are used in a lab?

A

Petri dishes

Centrifuge tubes

Tissue culture flask

Filters

Syringes

96 well plates

Pasteur pipettes / Stripettes

31
Q

Ionising Radiation, how is this involved with cleaning?

A

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

32
Q

How is Peroxide used as a chemical disinfectant?

A

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.

33
Q

How are Biguanides used as a chemical disinfectant?

A

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.

34
Q

How is QAT’s used as a chemical Disinfectant?

A

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

Microbiology and immunology (17 decks)

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