Microbiology Interview Questions and Answers in Pharma Company

1. What is Sterilization?

The process which destroys all the forms of microbial life including Fungus,Viruses & viable cells of micro-organisms along with their spores by using Chemical as well as Physical methods is called sterilization.

There are major 2 methods of sterilizationas:

1. Physical method 

a) Heating

Dry heat sterilization:160°C-180°C for 1.5hrs For glass wares & Heat stable compounds.

Example: Hot air oven.

Moist heat sterilization: 121°C-134°C under 15 lbs (1.1 bar) pressure for 15-20 min.

To achieve sterility, a holding time of at least 15 min at 121°C (250 °F) at 100 kPa (15 psi) or 3 min at 134 °C (273 °F) at 100 kPa (15 psi) is required.

Example: Autoclave.

b) Radiation

  • a process of killing microbes by using UV rays, Gamma rays. 
  • used to destroy bacterial DNA.
  • used for heat sensitive products.

c) Filtration

  • Complete removal of microbes is carried out by filter.
  • 0.22micron diameter cellulose filter is used.

2. Chemical Method

Chemical sterilization involves the utilization of certain chemicals so as to cause microbial termination. For this, the most used materials are chlorine, formaldehyde, glutaraldehyde, quaternary ammonium salts, and ETO.

Related: Major Sources of Contamination in the Sterile Area

2. How LAF Work?

In a laminar flow hood the air is passed through a HEPA (High Efficiency Particulates Air) filter which removes all airborne contamination to maintain sterile conditions.

Now the sterile air flows into the working (flasking) area where you can do all your flasking work without risk of contamination.

3. What is the specification of HEPA and ULPA Filters?

  • HEPA FILTERS (High efficiency particulate air): Removes 99.97% of contaminant particles about of 0.3um diameter size.
  • ULPA FILTERS (Ultra-low particulate air): More efficient than HEPA filter removes 99.999% of contaminants of 0.12um diameter size.

4. Give some examples of Gram +ve & Gram -ve Bacteria.

Gram Positive Bacteria
  • Streptococcus
  • Staphylococcus 
  • Streptomyces
  • Mycobacteriumtb 
  • Clostridiumbotulinm
Gram Negatve Bacteria
  • E.coli
  • Salmonella
  • Pseudomonas
  • Acetobacter
  • Rickttesia

5. Give some examples of Fungus.

  • A. niger
  • A. flavus
  • Candida aureus
  • Penicillium crysogenum
  • Penicillium notatum

6. What is Disinfection?

Disinfection is the process of removing or killing the all the form of microbial life except bacterial spores is called disinfection.

In Pharmaceuticals mostly 70% Isopropyl alcohol (70% IPA) is used as the disinfectant.

7. Why 70% Isopropyl alcohol is used as disinfectant in pharmaceutical industries,why not 100%?

The reason is behind the mode of action of 70% IPA is that -the Bacterial cells have proteins in their cell wall and when this protein comes in contact with the 70% IPA during disinfectant application, coagulation of proteins takes places in which denaturation of proteins occurred and after that IPA penetrate in the interior of the cell which cause lysis or death of the cell. 

Protein coagulation also happens in case of 100% IPA but with very fast rate and because of this very fast protein coagulation process denatured protein forms protective layer outside of the cell.When this happens, 100% can not penetrate inside the cell and not able to kill the microbe. 

Another factor is contact time, 70% IPA takes longer time to evaporate from any surface hence get enough contact time and in this mean time its how its efficacy but in case of 100% IPA, evaporation will be very fast, contact time will be less and it will not be so effective against microbes.That's why 70% IPA solution is used as disinfectant in pharmaceuticals industries.

8. What are antiseptics?

Antiseptics are the chemical substances which are used in destroying disease causing microorganisms (also called pathogens) externally on wounds or applied on skin surface to treat infection.
Example: Sanitizer

9. What is CFU?

A colony-forming unit (CFU) is a unit that is used to estimate the number of viable bacteria or fungal cells in a sample. Colony forming units are used as a measure of the number of micro-organisms present in or on surface of a sample.

To determine the number of colony forming units, a sample is prepared and spread or poured uniformly on a surface of an agar plate and then incubated at some suitable temperature for a number of days.The colonies that  forms are counted.

10. What is Bioburden testing?

Bioburden testing is performed to determine the total number of aerobic viabl microorganisms in or on a medical device, container or component after completion of all in-process steps prior to sterilization.

11. What are Selective, Differential, Enriched, Nutrient and Minimal media?

In microbiology, we use different type of media on routine basis. Different media have different properties and used for different type of microorganisms. Different types of media are mentioned below:

Selective Media

Selective media are those media which are used to support growth of one group of microorganisms but inhibit the growth of other group of microorganisms.

For example incase of Mannitol salt agar media. It contains very high amount of salt (7.5%) which inhibit the growth of gram negative bacteria and it is selective for gram positive bacteria like staphylococcus.

Differential Media

Differential media are those media which are used to distinguish closely related microorganisms based on their morphology on different agar media. 

For example in case of Mannitol salt agar, it contains mannitol and phenol red as pH indicator which support the growth of mannitol fermenting staphylococcus. Acid produced due to mannitol fermentation is detected and due to presence of phenol red indicator dye staphylococcus shows yellow coloured colonies on mannitol salt agar media.

Enriched media

These medi asupport the growth of wide variety of microorganisms and doesn't inhibit the growth of microorganisms.These media contains high amount of nutrients and mainly used to harvest the all types of microorganism which are present in the sample. For example Soyabean casein digest medium isused for enrichment of samples.

Nutrient media

These media are also called general purpose media. These media are nonselective and they contain general nutrients which required for the growth of wide range of microorganisms.

Soyabean casein digest agar and Nutrient agar are the example of this type of media.

Minimal media

Minimal media are those media which contains minimal nutrients for the growth of microorganisms. These media are mainly used for fastidious microorganisms. R2A media is an example of minimal media in which nutrients are present in very small amount.

12. What is BET test?

It is the Microbiological test which carried out to detect the presence of Bacterial endotoxin present in the given sample.

This endotoxin test is als ocalled as LAL Test because in this test the 'Limulus Amebocyte Lysate' isused which is the aqueous extract of blood cells of Horse shoecrab.

13. What is pyrogen testing?

This method is carried out to detect the presence of pyrogen.(Ames test)

14. What are the major method for pharmaceutical environment monitoring?

There are major following methods of environment monitoring in pharmaceutical indusrty as -
1. Settle plate method
2. Contact plate method
3. Swab testing
4. Air sampler
5. Personnel monitoring

Related: Pyrogens and Endotoxin Control in Cleanroom

15. What is the principle of bacterial staining?

The basic principle of gram staining involves the ability of the bacterial cell wall to retain the crystal violet dye during solvent treatment. Gram-positive microorganisms have higher peptidoglycan content, whereas gram-negative organisms have higher lipid content.

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