How Does Microbiology Contribute to Quality Assurance?

Microbial Limit Testing

Tests:

  • Total Aerobic Microbial Count (TAMC)
  • Total Yeast and Mold Count (TYMC)
  • Test for Specified Microorganisms (e.g., E. coli, salmonella spp..)

Acceptance Limits:

As per WHO and USP <61>:

  • TAMC: ≤ 10³ CFU/g or mL.
  • TYMC: ≤ 10² CFU/g or mL.
  • Specified microorganisms: Must be absent (e.g., E. coli, Salmonella spp.).


Sterility Testing

Tests:

  • Membrane filtration (for liquid products).
  • Direct inoculation (for solid or viscous products).

Microorganisms Tested:

  • General sterility testing checks for absence of all viable microorganisms, including Bacillus subtilis, Candida albicans, Aspergillus brasiliensis, etc.

Acceptance Limits:

  • No growth in the test samples.


Endotoxin Testing (Bacterial Pyrogens)

Tests:

  • Limulus Amoebocyte Lysate (LAL) test.

Microorganisms Tested:

  • Escherichia coli (used for endotoxin standards).

Acceptance Limits:

  • Varies depending on the product, expressed as Endotoxin Units (EU/mL).
  • Example: ≤ 0.5 EU/mL for water for injection (WFI).


Environmental Monitoring

Tests:

  • Settle plate method.
  • Active air sampling.
  • Surface sampling (contact plates or swabs).

Microorganisms Tested:

  • Various environmental flora, e.g., Bacillus spp., Cladosporium spp.

Acceptance Limits (as per WHO/GMP):

  • Grade A (sterile): Zero CFU/m³ (air), ZERO CFU/plate (surface).
  • Grade B: 10 CFU/m³ (air), 5 CFU/plate (surface).


Water Testing

Tests:

  • Microbial enumeration test.
  • Test for Pseudomonas aeruginosa.
  • Test for endotoxins.

Microorganisms Tested:

  • Pseudomonas aeruginosa, coliforms, and other Gram-negative bacteria.

Acceptance Limits (WHO):

  • Purified Water: ≤ 100 CFU/mL.
  • WFI: ≤ 10 CFU/100 mL.


Antimicrobial Effectiveness Testing (AET)

Tests:

  • Challenge test: Deliberate inoculation with specific microorganisms.

Microorganisms Used:

  • Escherichia coli.
  • Staphylococcus aureus.
  • Pseudomonas aeruginosa.
  • Candida albicans.
  • Aspergillus brasiliensis.

Acceptance Limits:

  • No increase in microbial counts over the test period; significant reduction within 7 days.


Bioburden Testing

Microorganisms Tested:

  • General bioburden includes all viable organisms.

Acceptance Limits:

  • Depends on product type and stage in production.


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Resource Person: Bettahar Nadir

Categories: Microbiology, Q&A
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