Can pus for culture and sensitivity (C&S) be stored in a freeze for 12 hours in case of a delay?

Proper Storage of Pus Samples for Culture and Sensitivity

Pus samples for culture and sensitivity should NOT be stored in a freezer but should be refrigerated at 4°C if processing will be delayed for up to 12 hours. 1

Recommended Storage Conditions for Pus Samples

• Pus samples should be processed as soon as possible after collection to ensure optimal recovery of microorganisms and accurate sensitivity results 1
• If immediate processing is not possible, samples should be stored at 4°C (refrigerated) for up to 12 hours, not frozen 1
• Freezing can damage bacterial cells and affect the viability of microorganisms, potentially leading to false-negative culture results 1, 2
• Storage at room temperature beyond 1 hour is not recommended as it may allow overgrowth of certain organisms and death of fastidious pathogens 3

Impact of Delayed Processing on Sample Quality

• Delayed processing without proper refrigeration can lead to:
  • Altered microbial counts due to continued bacterial growth or death 4
  • Increased reactive oxygen species (ROS) that can damage bacterial cells 4
  • Development of viable but non-culturable (VBNC) bacteria that won't grow on culture media despite being present 4
  • Changes in the relative proportions of different organisms in polymicrobial infections 5

Proper Collection and Transport Procedures

• Collect pus samples in sterile containers that do not promote cell adherence to container surfaces 1
• If processing will be delayed by 30-60 minutes, transport the sample at 4°C (on ice) 1
• For delays exceeding 1 hour but less than 12 hours, refrigeration at 4°C is essential 1, 3
• Do not freeze pus samples as this can compromise microbial viability 1, 2

Special Considerations

• For superficial soft tissue abscesses, the microbial flora is often predictable, and empiric antibiotics may be started before culture results are available 5
• If sample processing will be delayed beyond 12 hours, consider adding appropriate transport media to preserve bacterial viability, though this is not ideal 1
• Samples stored improperly may yield false-negative results or misrepresent the true microbial composition 4, 2

Common Pitfalls to Avoid

• Never freeze pus samples intended for culture and sensitivity as freezing damages bacterial cell membranes 1, 2
• Avoid storing samples at room temperature for extended periods as this allows for bacterial overgrowth or death 3, 4
• Do not delay processing beyond 12 hours even with refrigeration, as this significantly reduces recovery of fastidious organisms 1
• Avoid repeated freeze-thaw cycles if samples must be stored for other types of analysis, as this causes significant damage to cellular components 2