Sterilization And Disinfection In Microbiology Multiple Choice Question And Answer

Question 1. Pasteurization Of Milk Is Done At

1. 73°C for 20 min
2. 63°C for 20 min
3. 73°C for 30 sec
4. 63°C for 30 sec

Answer. (2) (63°C FOR 20 MIN)

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Question 2. Biological indicator for determining efficacy of autoclaving is:

1. Pseudomonas aeruginosa
2. Clostridium perfingens
3. Bacillus stearothermophilus
4. Salmonella typhi

Answer. (3) (Bacillus stearothermophilus)

• Geobacillus stearothermophilus is used for autoclave, hydrogen peroxide gas plasma and liquid acetic acid sterilizer
• Bacillus atrophaeus is used for ethylene oxide sterilizer and dry heat

Question 3. Best chemical disinfectant to disinfect stethoscope is:

1. Isopropyl alcohol
2. Ethylene oxides
3. Halogenated compound
4. Steam plasma sterilization

Answer. (1) (Isopropyl alcohol)

Low-level disinfectant such as Isopropyl alcohol should be enough as stethoscope is a noncritical item according to Spaulding’s classification.

Question 4. Inspissation is heating:

1. At 85 deg C for half an hour on 3 consecutive days
2. 85 deg C for an hour
3. At 100 deg C for half an hour on 3 consecutive days

Answer. (1) (At 85 deg C for half…)30

Question 5. Pasteurization of milk is done at:

1. 63°C for 30 min
2. 72°C for 30 min
3. 63°C for 20 min
4. 72°C for 20 min

Answer. (1) (63°C for 30 min)

• Pasteurization of milk is done by – Holder’s method (63°C for 30 min) or Flash method(72°C for 20 sec) followed by rapid cooling to 13°C.
• All non-spring pathogens are killed except Coxiella which survives Holder’s method.

Question 6. Sterilization accuracy is assessed by using:

1. Clostridium perfringenes
2. Geobacillus stearothermophilus
3. Staphylococcus aureus
4. Clostridium botulinum

Answer. (2) (Geobacillus stearothermophilus)

• Geobacillus stereothermophilus is used as biological sterilization control for autoclave,hydrogen peroxide gas plasma and liquid acetic acid sterilizer.

Question 7. Best method of sera sterilization is:

1. Filtration
2. Autoclaving
3. Radiation
4. Heating

Answer. (1) (Filtration)

Filtration is the best method of sterilization of heat labile liquids such as sera and solutions of sugars or antibiotics, toxins and vaccines. It helps to remove bacteria.

Question 8. Which of the following is used to test the efficiency of sterilization in an autoclave?

1. Clostridium tetani
2. Bacillus stearothermophilus
3. Bacillus pumilus
4. Bacillus cereus

Answer. (2) (Bacillus stearothermophilus)

• Biological Sterilization Indicator: (Detail list— Refer text)
• Autoclave: B. stearothermophillus
• Hot air oven: Clostridium tetani nontoxigenic strain

Question 9. Spore of which bacteria is used as sterilization control of Plasma sterilization:

1. B. subtilis
2. B. pumilis
3. Cl. tetani
4. B. stearothermophilus

Answer. (4) (B. stearothermophilus)

Biological Sterilization Indicator of plasma sterilization: B. stearothermophillus, B. subtilis subspecies niger (Detail list— Refer text)

Question 10. Condition required for autoclave is?

1. 121°C temperature for 20 min
2. 121°C temperature for 15 min
3. 100°C temperature for 60 min
4. 100°C temperature for 90 min

Answer. (2) (121°C temperature….)

• Autoclave: Recommended condition- 121–124°C temperature for 15 min at 1.1 bar pressure
• Alternate: 126°C for 10 minutes at pressure of 20 psi or 133°C for 3 minutes at pressure of 30 psi.
• Hot air oven: 160°C temperature for 120 min or 180°C temperature for 30 min

Question 11. Which of the following is most resistant to sterilization?

1. Cysts
2. Prions
3. Spores
4. Viruses

Answer. (2) (Prions)

• Prions are the highest resistance structure

Question 12. Choose the correct ones for the decreasing order of resistance to sterilization:

1. Prions, Bacterial spores, Bacteria
2. Bacterial spores, Bacteria, Prions
3. Bacteria, Prions, Bacterial spores
4. Bacterial spores, Prions, Bacteria

Answer. (1) (Prions, Bacterial spores, Bacteria)

Question 13. STERRAD is a gas plasma sterilizer used in operation theatres for disinfecting OT articles. Which of the following is the active agent used in it?

1. H2O2
2. N2O
3. Ozone
4. EtO

Answer. (1) (H2O2)

• The active agent used for gas plasma sterilizer is hydrogen peroxide

Question 14. Which of the following disinfectants is used to clean blood spill in OT?

1. Chlorine-based
2. Phenol based
3. Alcohol-based
4. Quaternary ammonium compound

Answer. (1) (Chlorine based)

• Spill management should be carried out by hypochlorite- 1% for small spill and 10% for large spill

Question 15. Chlorine disinfection of water is due to which ion?

1. Hypochlorous acid
2. Hypochlorite ion
3. Hydrogen ion
4. Hydrochloric acid

Answer. (1) (Hypochlorous acid)

Question 16. Bacterium that often contaminates disinfectant solutions is:

1. Staphylococcus aureus
2. Streptococcus
3. E. coli
4. Pseudomonas

Answer. (4) (Pseudomonas)

• Pseudomonas is resistant to no. of disinfectant solutions such as savlon or Dettol.

Question 17. Bleaching powder, the active component is:

1. Hypochlorous acid
2. Chloroxylenol
3. Cetrimide
4. Chlorhexidine

Answer. (1) (Hypochlorous acid)

• Hypochlorous acid is the active component of Bleaching powder.

Question 18. Low-Level disinfectant is:

1. Benzalkonium chloride
2. Isopropyl alcohol
3. Glutaraldehyde
4. Hydrogen peroxide

Answer. (1) (Benzalkonium chloride)

• Isopropyl alcohol, Phenol: Intermediate level disinfectant
• Quaternary ammonium compounds like Benzalkonium chloride: Low level disinfectant
• Glutaraldehyde, formaldehyde, Hydrogen peroxide, Chlorine: High level disinfectant.

Question 19. Heart-lung machine is best sterilized by:

1. Cidex
2. Ethylene oxide
3. Isoprophyl alcohol
4. Formaldehyde

Answer. (2) (Ethylene oxide)

• Heart lung machines, respirators and dental equipments are best sterilized by Ethylene oxide.

Question 20. Best disinfectant for endoscopes is:

1. Hypochlorite
2. Formaldehyde
3. Glutaraldehyde
4. Chlorhexidine

Answer. (3) (Glutaraldehyde)

2% Glutaraldehyde and Ortho-phthalaldehyde (0.55%) are recommended disinfectants for endoscopes.

Question 21. Prions are best killed by:

1. Autoclaving at 121°C
2. 5% formalin
3. Sodium hydroxide for 1 hr
4. Sodium hypochloride for 10 min

Answer. (3) (Sodium hydroxide for 1 hour)

Prions are sterilized by: 0.5% Sodium hypochlorite for 2 hr or 1N NaOH for 1 hour or Autoclave for 134°C for 1–1.5 hour

Question 22. Sterilization of fiberoptic is done by:

1. Glutaraldehyde
2. Chlorine
3. Autoclave
4. Phenol

 Answer. (1) (Glutaraldehyde)

• A fiber optic is a flexible, transparent fiber made of high quality extruded glass (silica) or plastic used for laryngoscopes.
• Fiberoptic laryngoscopes are best sterilized by Glutaraldehyde or ortho-ophthaldehyde.

Question 23. According to Spaulding classification, laparoscope and arthroscopic instruments are under:

1. Critical item
2. Semi critical item
3. Noncritical item

Answer. (1) (Critical item)

Question 24. Which is false about spaulding classification?

1. Noncritical items also included in classification
2. Semicritical items— contact with mucus membrane
3. Semicritical items— needs low disinfectant
4. Cardiac catheter, e.g. of critical items

Answer. (3) (Semicritical items— needs low disinfectant)

• Semicritical items are those that come in contact with mucous membranes or minor skin breaches and they need high level disinfectant for sterilization.

Question 25. Phenol coefficient indicates:

1. Efficacy of a disinfectant
2. Dilution of a disinfectant
3. Quantity of a disinfectant
4. Purity of a disinfectant

Answer. (1) (Efficacy of a disinfectant)

• Testing efficacy of disinfectants by Phenol coefficient (Rideal Walker ) test – Phenol coefficient is determined by the dilution of the disinfectant in question which sterilizes the suspension of S. typhi in a given time divided by the dilution of phenol which sterilizes the suspension in the same time.

Question 26. Sputum can be disinfected by all except:

1. Autoclaving
2. Boiling
3. Cresol
4. Chlorhexidine

Answer. (4) (Chlorhexidine)

• The commonest pathogen suspected to be present in sputum— Tubercle bacilli. So it has to be disinfected by an appropriate technique.
• Chlorhexidine (2-4%) is a skin antiseptic, used for burns or hand disinfection. It is not mycobactericidal.
• Sputum can be disinfected by:
  • Autoclaving: Ideal method
  • Other methods include: Burning of the material, Cresol 5% or Phenol or Boiling

Question 27. Surgical blade is sterilized by:

1. Gamma radiation
2. Hot air oven
3. Steaming

Answer. (1) (Autoclave)

• Steam is the preferred method for sterilizing critical medical and surgical instruments that are not damaged by heat, steam, pressure, or moisture………… CDC Guideline, 2008
• Metal instruments and surgical blades are better sterilized by autoclave.

Question 28. Sporicidal agents are:

1. Glutaraldehyde
2. Ethylene oxide
3. Formaldehyde
4. Benzalkonium chloride
5. Chlorine

Answer. (1, 2, 3) (Glutaraldehyde, Ethylene oxide, Formaldehyde)

• Benzalkonium chloride is a surface active agent, widely used as wetting agents,detergents, and emulsifiers.

Question 29. Savlon contains:

1. Cetrimide + Chlorhexidine
2. Cetrimide + Butyl alcohol
3. Cetrimide + Chlorhexidine + Butyl alcohol
4. Cetrimide + Cetavlon

Answer. (1) (Cetrimide + Chlorhexidine)

• Savlon contains— Cetrimide 3% (Cetavlon) + Chlorhexidine 0.3% (Hibitane)

Question 30. All of the following are the tests to check the efficiency of disinfectant except:

1. Chick Martin test
2. Riedel Walker test
3. Hugh Leifson test d. Kelsey Sykes test

Answer. (3) (Hugh Leifson test)

• Hugh Leifson test is used to differentiate micrococci (oxidizer) from staphylococci (fermenter).