Moist Heat Sterilization

Moist Heat Sterilization

Q. 1

 

The chamber condition required for autoclaving with respect to the temperature-time is which of the following?

 A

121°C temperature for 20 min

 B

121°C temperature for 15 min

 C

100°C temperature for 60 min

 D

100°C temperature for 90 min

Q. 1

 

The chamber condition required for autoclaving with respect to the temperature-time is which of the following?

 A

121°C temperature for 20 min

 B

121°C temperature for 15 min

 C

100°C temperature for 60 min

 D

100°C temperature for 90 min

Ans. B

Explanation:

Moist heat sterilization, usually autoclaving, is the most frequently used method of sterilization.

Bacterial spores which are resistant to boiling are sterilized using autoclaving.

Autoclaving is done in a chamber in which steam, at a pressure of 15 lb/in2, reaches a temperature of 121°C and is held at that temperature for 15 to 20 minutes. 

  • Sterilization by dry heat requires  temperatures in the range of 180°C for 2 hours. It is used primarily for glassware.
  • Pasteurization involves heating the milk to 62°C for 30 minutes followed by rapid cooling. It is sufficient to kill the vegetative cells of the milk-borne pathogens (e.g., Mycobacterium bovis, Salmonella, Streptococcus, Listeria, and Brucella).

Ref: Review of Medical Microbiology and Immunology, 12e, Chapter 13


Q. 2

The phosphatase test was applied to milk to determine whether pasteurization was done properly after an outbreak of Listeria monocytogenes in pasteurized milk. 

 
Assertion: The thermal resistance of alkaline phosphatase has been considered to be greater than that of any non-spore-forming pathogens that might be found in milk.
 
Reason: Raw milk contains the enzyme lactoperoxidase which is destroyed on heating at a temperature which corresponds closely with the standard time and temperature required for pasteurization.
 
 A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

 B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

 C

Assertion is true, but Reason is false

 D

Assertion is false, but Reason is true

Q. 2

The phosphatase test was applied to milk to determine whether pasteurization was done properly after an outbreak of Listeria monocytogenes in pasteurized milk. 

 
Assertion: The thermal resistance of alkaline phosphatase has been considered to be greater than that of any non-spore-forming pathogens that might be found in milk.
 
Reason: Raw milk contains the enzyme lactoperoxidase which is destroyed on heating at a temperature which corresponds closely with the standard time and temperature required for pasteurization.
 
 A

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion

 B

Both Assertion and Reason are true, and Reason is not the correct explanation for Assertion

 C

Assertion is true, but Reason is false

 D

Assertion is false, but Reason is true

Ans. C

Explanation:

Phosphatase test is widely used to check the efficiency of pasteurization.

Raw milk contains an enzyme called phosphatase which is destroyed on heating at a temperature which corresponds closely with the standard time and temperature required for pasteurization.

At 60 deg C for 30 minutes phosphatase is completely destroyed.

Ref: Park’s Textbook of Preventive and Social Medicine, 20th Edition, Page 569.

 


Q. 3

Bacterial spores are hest destroyed by-

 A

UV rays

 B

Autoclaving at 121°C for 20 mints

 C

Hot air Oven

 D

Infrared rays

Q. 3

Bacterial spores are hest destroyed by-

 A

UV rays

 B

Autoclaving at 121°C for 20 mints

 C

Hot air Oven

 D

Infrared rays

Ans. B

Explanation:

Ans. is ‘b’ i.e., Autoclaving at 121°c for 20 minutes

Autoclaving

.   Autoclaving is a method to sterilize equipment by subjecting them to high pressure at 121°C or more.

.   It is sterilization by steam under pressure.

.   The device which is used for autoclaving is known as autoclave.


Q. 4

Culture media are sterilized by –

 A

Autoclaving

 B

Beta- radiation

 C

Hot air oven

 D

All

Q. 4

Culture media are sterilized by –

 A

Autoclaving

 B

Beta- radiation

 C

Hot air oven

 D

All

Ans. A

Explanation:

Ans. is ‘a’ i.e., Autoclaving


Q. 5

Pasteurization is____________________disinfection

 A

Precurrent

 B

Concurrent

 C

Preconcurrent 

 D

Terminal

Q. 5

Pasteurization is____________________disinfection

 A

Precurrent

 B

Concurrent

 C

Preconcurrent 

 D

Terminal

Ans. A

Explanation:

Ans. is ‘a’ i.e., Precurrent 

1. Types of disinfection

Precurrent (prophylactic) disinfection

o It is done as a preventive method (person is not ill).

o For example –> Chlorination of water, pasteurization of milk, Handwashing.

Concurrent disinfection

2. It is done when person is ill.

o It is the application of disinfective measures as soon as possible after the discharge of infectious material from the body of patient or after the soiling of articles with such material, i.e., the disease agent is destroyed as soon as it is released from the body, and in this way further spread of the agent is stopped.

o e.g., disinfection of urine, faeces, vomit, contaminated linen, clothes, hands, dressing, aprons, gloves etc.

3. Terminal disinfection

o It is the application of disinfective measures after the patient has taken discharge from hospital or he/she has died. e.g., disinfection of hospital rooms & floor, burning or burial of soiled material.

Before illness                         Precurrent disinfection

Illness                                     Concurrent disinfection

After illness                            Terminal disinfection


Q. 6

Disinfection by autoclaving is NOT recommended for-

 A

Sputum

 B

Linen

 C

Sharp instruments

 D

All

Q. 6

Disinfection by autoclaving is NOT recommended for-

 A

Sputum

 B

Linen

 C

Sharp instruments

 D

All

Ans. C

Explanation:

Ans. is ‘c’ i.e., Sharp instruments 


Q. 7

True about Pasteurization of milk is all except 

 A

Does not kill thermoduric bacteria

 B

Does not kill spores

 C

Cause > 95% decrease in bacterial count

 D

Kills tubercle bacillus

Q. 7

True about Pasteurization of milk is all except 

 A

Does not kill thermoduric bacteria

 B

Does not kill spores

 C

Cause > 95% decrease in bacterial count

 D

Kills tubercle bacillus

Ans. C

Explanation:

Ans. is ‘c’ i.e., “Causes > 95% decrease in bacterial count

Pasteurization

Pasteurization is done to destroy the pathogens that may be present in milk, while causing minimal change in the composition. flovour and nutritive value.

a Pasteurization kills nearly 90% of the bacteria in milk, including the more heat resistant – Tubercle bacilli – Qfever organisms

o It does not kill the thermoduric bacteria.

o It does not kill bacteria spores.

There are 3 w idelv used methods for pasteurization :

a.     Holder method : Milk kept at 63-66°C fur 30 minutes is rapidly cooled to 5°C.

b.  HTST method : ‘High temperature short time’ method (Flash method)

  • I leated to 72°C for 15 sec. and then rapidly cooled to 4°C
  • This is now the most widely used method.

method :

  • Ultra-high temprature method.
  • Rapidly heated in two stages to 125°C for few seconds.
  • The second stage is being under pressure.
  • It is then rapidly cooled.

Q. 8

The following tests are used to check the efficiency of pasteurization of mild except –

 A

Phosphatase test

 B

Standard plate count

 C

Coliform count

 D

Methylene blue test

Q. 8

The following tests are used to check the efficiency of pasteurization of mild except –

 A

Phosphatase test

 B

Standard plate count

 C

Coliform count

 D

Methylene blue test

Ans. D

Explanation:

Ans is ‘d’ i.e., Methylene blue test

`Methylene blue Reduction test’ is an indirect test Jar detection of microorganism in milk. It is carried out on milk prior to the process of pasterurization and is not used to check the efficiency of pasteruization.


Q. 9

Which is not used in pasteurization ‑

 A

Phosphatase test

 B

Methylene blue test

 C

Coliform count

 D

Standard plate count

Q. 9

Which is not used in pasteurization ‑

 A

Phosphatase test

 B

Methylene blue test

 C

Coliform count

 D

Standard plate count

Ans. B

Explanation:

Ans. is ‘b’ i.e., Methylene blue test


Q. 10

Pasteurization of milk is achieved by boiling at –

 A

65°C for 30 min

 B

72° for 10 sec

 C

100°  for 20 sec

 D

136° for 30 sec

Q. 10

Pasteurization of milk is achieved by boiling at –

 A

65°C for 30 min

 B

72° for 10 sec

 C

100°  for 20 sec

 D

136° for 30 sec

Ans. A

Explanation:

Ans. is ‘a’ i.e., 65° C for 30 min 


Q. 11

The autoclave method of sterilization:

September 2004

 A

Is performed under atmospheric pressure

 B

Raising temperature to 120°C

 C

Utilizes dry heat

 D

All of the above

Q. 11

The autoclave method of sterilization:

September 2004

 A

Is performed under atmospheric pressure

 B

Raising temperature to 120°C

 C

Utilizes dry heat

 D

All of the above

Ans. B

Explanation:

Ans. B i.e. Raising temperature to 120°C


Q. 12

Pasteurization of milk is determined by:

September 2005, 2007 & 2009

 A

Methylene blue reduction test

 B

Phosphatase test

 C

Turbidity test

 D

Resazurin test

Q. 12

Pasteurization of milk is determined by:

September 2005, 2007 & 2009

 A

Methylene blue reduction test

 B

Phosphatase test

 C

Turbidity test

 D

Resazurin test

Ans. B

Explanation:

Ans. B: Phosphatase test

Alkaline Phosphatase (ALP) is an enzyme naturally present in all raw milks, which is used as an indicator of proper milk pasteurization. Complete pasteurization will inactivate the enzyme to below levels which are detectable by conventional methods. Because the heat stability of ALP is greater than that of pathogens which may be present in milk, the enzyme serves as an indicator of product safety.

The classic test for the determination of alkaline phosphatase activity is the Scharer Rapid Phosphatase Test. Turbidity test checks sterilisation of milk and distinguishes between pasteurized and sterilised milk. Methylene blue reduction test is done for determining viable bacterial count in the milk.

Resazurin test is similar to Methylene blue reduction test but employs dye Resazurin in place of methylene blue.


Q. 13

True about autoclaving is:      

March 2007

 A

115 degree C at for 20 min

 B

121 degree C at for 15 min

 C

118 degree C at for 15 min

 D

124 degree C at for 15 min

Q. 13

True about autoclaving is:      

March 2007

 A

115 degree C at for 20 min

 B

121 degree C at for 15 min

 C

118 degree C at for 15 min

 D

124 degree C at for 15 min

Ans. B

Explanation:

Ans. B: 121 degree C at for 15 min

Sterilization refers to any process that effectively kills or eliminates transmissible agents (such as fungi, bacteria, viruses, prions and spore forms etc.) from a surface, equipment, foods, medications, or biological culture medium.

Sterilization can be achieved through application of heat, chemicals, irradiation, high pressure or filtration. It may be defined as:

Physical sterilization includes:

  • Heat sterilization
  • Radiation sterilization

Chemical sterilization includes:

  • Ethylene oxide
  • Ozone
  • Chlorine bleach
  • Glutaraldehyde
  • Formaldehyde
  • Hydrogen peroxide
  • Peracetic acid

Heat Sterilization

A widely-used method for heat sterilization is the autoclave

Autoclaves commonly use steam heated to 121 °C or 134 °C.

To achieve sterility, a holding time of at least 15 minutes at 121 °C or 3 minutes at 134 °C is required.

Additional sterilizing time is usually required for liquids and instruments packed in layers of cloth, as they may take longer to reach the required temperature.

After sterilization, autoclaved liquids must be cooled slowly to avoid boiling over when the pressure is released.

Proper autoclave treatment will inactivate all fungi, bacteria, viruses and also bacterial spores, which can be quite resistant. Indicator tape is often placed on packages of products prior to autoclaving. A chemical in the tape will change color when the appropriate conditions have been met.

Biological indicators (“bioindicators”) can also be used to independently confirm autoclave performance. Most contain spores of the heat resistant microbe Bacillus stearotliermophilus, among the toughest organisms for an autoclave to destroy. If the autoclave destroyed the spores, the medium will remain its original color. If autoclaving was unsuccessful the B. sterothermophilus will metabolize during incubation, causing a color change during the incubation.


Q. 14

Biological indicator for determining efficacy of autoclaving is:    

September 2009

 A

Pseudomonas aeruginosa

 B

Clostridium Perfringenes

 C

Bacillus stearothermophilus

 D

Salmonella typhi

Q. 14

Biological indicator for determining efficacy of autoclaving is:    

September 2009

 A

Pseudomonas aeruginosa

 B

Clostridium Perfringenes

 C

Bacillus stearothermophilus

 D

Salmonella typhi

Ans. C

Explanation:

Ans. C: Bacillus stearothermophilus


Q. 15

Autoclaving is done at what temperature for 15 minutes:

March 2010

 A

118 degree C

 B

121 degree C

 C

126 degree C

 D

134 degree C

Q. 15

Autoclaving is done at what temperature for 15 minutes:

March 2010

 A

118 degree C

 B

121 degree C

 C

126 degree C

 D

134 degree C

Ans. B

Explanation:

Ans. B: 121 degree C


Q. 16

Best indicator for sterilization by autoclaving ‑

 A

Bacillus subtilis

 B

Geobacillus

 C

Bacillus pumilis

 D

Clostridium

Q. 16

Best indicator for sterilization by autoclaving ‑

 A

Bacillus subtilis

 B

Geobacillus

 C

Bacillus pumilis

 D

Clostridium

Ans. B

Explanation:

Ans. is ‘b’ i.e., Geobacillus

Biological indicators

  • Biological indicators are standardised preparations of microorganisms used to assess the effectiveness of a sterilization process.
  • They usually consist of a population of bacterial spores placed on an inert carrier, for example a strip of filter paper, a glass slide or a plastic tube.
  • Most commonly, spores of Bacillus stereothermophilus (Geobacillus stearothermophilus) are used. Spores of Bacillus subtilis and Bacillus pumilis are alse used.


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