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Microbiology

Time & Temperature

Time and temperature are critical factors in maintaining the viability and integrity of microorganisms during transport from the point of collection to the laboratory. Different organisms have different requirements, and adhering to recommended time and temperature guidelines is crucial for accurate and reliable laboratory results

Importance

  • Maintaining Viability: Proper time and temperature conditions prevent the death of microorganisms during transport
  • Preventing Overgrowth: Controlling time and temperature can prevent the overgrowth of certain organisms, ensuring that the pathogens of interest can be detected
  • Preserving Specimen Integrity: Appropriate time and temperature conditions help maintain the integrity of the specimen, preventing degradation or alteration of the microorganisms
  • Ensuring Accurate Results: Proper time and temperature conditions during transport are essential for obtaining accurate and reliable test results, which are critical for patient care

General Guidelines

  • Minimize Transport Time: Transport specimens to the laboratory as soon as possible after collection
  • Maintain Appropriate Temperature: Store and transport specimens at the recommended temperature range
  • Follow Laboratory Guidelines: Adhere to the laboratory’s specific guidelines for specimen transport time and temperature
  • Document Deviations: Document any deviations from recommended time and temperature guidelines

Temperature Ranges

  • Refrigerated (2-8°C): Used for many bacterial, viral, and fungal specimens to slow down metabolic activity and prevent overgrowth
  • Room Temperature (20-25°C): Suitable for some bacterial specimens and for specimens where refrigeration may be detrimental
  • Frozen (-20°C or -70°C): Used for long-term storage of certain viral and molecular specimens
  • Body Temperature (35-37°C): Required for some fastidious organisms and for blood cultures

Specific Recommendations for Different Organisms and Specimen Types

Bacterial Specimens

  • General Recommendations
    • Transport most bacterial specimens at refrigerated temperatures (2-8°C) within 24-72 hours
    • Use appropriate transport media to maintain viability during transport
  • Specific Organisms
    • Neisseria gonorrhoeae: Transport at room temperature (20-25°C) or body temperature (35-37°C) within 6 hours. Use appropriate transport media (e.g., Amies with charcoal)
    • Campylobacter: Transport at refrigerated temperatures (2-8°C) within 24 hours. Use appropriate transport media (e.g., Cary-Blair)
    • Streptococcus pneumoniae: Transport at refrigerated temperatures (2-8°C) within 24 hours
    • Haemophilus influenzae: Transport at refrigerated temperatures (2-8°C) within 24 hours
    • Clostridium difficile: Transport stool specimens at refrigerated temperatures (2-8°C) within 48 hours

Viral Specimens

  • General Recommendations
    • Transport most viral specimens at refrigerated temperatures (2-8°C) within 48 hours
    • Use viral transport medium (VTM) to maintain viability during transport
    • For long-term storage, freeze specimens at -70°C
  • Specific Viruses
    • Respiratory viruses (influenza, RSV): Transport at refrigerated temperatures (2-8°C) within 48 hours
    • Herpes simplex virus (HSV): Transport at refrigerated temperatures (2-8°C) within 48 hours
    • Varicella-zoster virus (VZV): Transport at refrigerated temperatures (2-8°C) within 48 hours

Fungal Specimens

  • General Recommendations
    • Transport most fungal specimens at room temperature (20-25°C) or refrigerated temperatures (2-8°C) within 24-72 hours
    • Use appropriate transport media (e.g., Mycosel agar, Sabouraud dextrose agar)
  • Specific Fungi
    • Dermatophytes: Transport at room temperature (20-25°C) within 72 hours
    • Yeasts (Candida): Transport at room temperature (20-25°C) or refrigerated temperatures (2-8°C) within 72 hours
    • Molds: Transport at room temperature (20-25°C) within 72 hours

Mycobacterial Specimens

  • General Recommendations
    • Transport mycobacterial specimens at refrigerated temperatures (2-8°C) within 24 hours
    • Use appropriate transport media (e.g., Middlebrook 7H9 broth, Dubos broth)
  • Specific Mycobacteria
    • Mycobacterium tuberculosis: Transport at refrigerated temperatures (2-8°C) within 24 hours

Blood Cultures

  • General Recommendations
    • Transport blood culture bottles at body temperature (35-37°C) or room temperature (20-25°C) as soon as possible
    • Do not refrigerate blood culture bottles
    • Follow the blood culture system manufacturer’s instructions

Urine Specimens

  • General Recommendations
    • Transport urine specimens at refrigerated temperatures (2-8°C) within 24 hours
    • Use urine transport tubes with preservatives to maintain bacterial counts during transport
  • Unpreserved urine: Transport at refrigerated temperatures (2-8°C) within 2 hours

Common Errors and How to Avoid Them

  • Delay in Transport: Transport specimens to the laboratory as soon as possible
  • Improper Temperature Storage: Store and transport specimens at the recommended temperature range
  • Failure to Use Appropriate Transport Media: Select transport media that are appropriate for the organisms being tested for
  • Refrigerating Blood Cultures: Do not refrigerate blood culture bottles
  • Failure to Document Deviations: Document any deviations from recommended time and temperature guidelines

Key Terms

  • Viability: The ability of microorganisms to survive and reproduce
  • Transport Medium: A liquid or gel that is used to maintain the viability of microorganisms during transport
  • Refrigerated: Stored at 2-8°C
  • Room Temperature: Stored at 20-25°C
  • Frozen: Stored at -20°C or -70°C
  • Body Temperature: Stored at 35-37°C
  • Fastidious Organisms: Organisms with complex nutritional requirements