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SOP-025: Detection of Cell Culture Contamination

Purpose​

To provide a standardized procedure for the routine detection, documentation, and reporting of contamination in mammalian cell cultures.

Scope​

This SOP applies to the routine examination of adherent and suspension mammalian cell cultures for bacterial, fungal, yeast, and suspected mycoplasma contamination.

Responsibilities​

The operator is responsible for:

  • Inspecting cultures before every manipulation.
  • Recognizing signs of contamination.
  • Isolating suspected contaminated cultures.
  • Recording observations and notifying the laboratory supervisor.

Required Materials​

Equipment​

  • Inverted microscope
  • Class II Biosafety Cabinet
  • Cell culture vessels
  • Laboratory notebook or electronic record system
  • Personal protective equipment (PPE)

Procedure​

1. Inspect the Culture Vessel​

Before opening the culture vessel, examine:

  • Medium clarity
  • Medium color
  • Presence of floating particles
  • Integrity of the culture vessel

2. Microscopic Examination​

Using an inverted microscope, assess the culture for:

  • Cell morphology
  • Cell attachment
  • Cellular debris
  • Unusual particulate movement
  • Fungal hyphae or yeast-like structures
  • Abnormal cell behavior

3. Assess the Culture​

Compare observations with the expected appearance of the cell line.

If contamination is suspected:

  • Do not use the culture for experiments.
  • Clearly label the culture as Suspected Contamination.
  • Separate it from uncontaminated cultures pending further investigation.

4. Document Findings​

Record:

  • Type of abnormality observed
  • Culture identification
  • Date and time
  • Operator initials

5. Report the Incident​

Report suspected contamination according to laboratory procedures.

Proceed with confirmatory testing when required.

Acceptance Criteria​

ParameterAcceptance Criterion
Medium appearanceClear and free of visible particles
Cell morphologyTypical for the cell line
Culture vesselNo visible contamination
Microscopic examinationNo evidence of microorganisms

Critical Control Points​

  • Inspect cultures before every medium change or passage.
  • Compare cultures with previous observations whenever possible.
  • Examine multiple microscopic fields.
  • Do not ignore subtle morphological changes.
  • Isolate suspected contaminated cultures immediately.

Documentation​

Record the following:

  • Date
  • Cell line
  • Passage number
  • Culture vessel
  • Observations
  • Suspected contamination type (if applicable)
  • Operator initials

Quality Control​

Verify:

  • Routine inspections are performed.
  • Observations are documented consistently.
  • Suspected cultures are isolated promptly.
  • Laboratory records are complete.

Troubleshooting​

ObservationPossible CauseCorrective Action
Medium becomes cloudyPossible bacterial contaminationIsolate the culture and investigate immediately
Filamentous structures observedPossible fungal contaminationRemove the culture from routine use and report the finding
Small refractile particles showing rapid movementPossible bacterial contaminationConfirm by further examination and discontinue use if contamination is verified
Gradual decline in cell growth without obvious contaminationPossible mycoplasma contaminationPerform routine mycoplasma testing

Safety Considerations​

  • Handle all cultures as potentially biohazardous.
  • Wear appropriate personal protective equipment (PPE).
  • Perform all manipulations in a certified Class II Biosafety Cabinet.
  • Minimize handling of suspected contaminated cultures.
  • Dispose of confirmed contaminated cultures according to institutional biosafety procedures.