Skip to main content

Microbiology

Atmosphere

The atmosphere in which a specimen is transported is a critical factor influencing the viability and recovery of microorganisms. Different organisms have different atmospheric requirements for survival and growth. Providing the appropriate atmosphere during transport is essential for accurate and reliable laboratory results

Importance

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

Types of Atmospheric Requirements

  • Aerobic: Requires the presence of oxygen for growth and survival
  • Anaerobic: Requires the absence of oxygen for growth and survival
  • Facultative Anaerobic: Can grow in the presence or absence of oxygen
  • Microaerophilic: Requires a reduced level of oxygen (typically 5-10%) for growth
  • Capnophilic: Requires an elevated level of carbon dioxide (typically 5-10%) for growth

Methods for Controlling Atmosphere During Transport

Aerobic Transport

  • General Considerations: Most aerobic organisms are relatively hardy and can survive in ambient air during transport
  • Swabs: Swabs in transport media (e.g., Amies medium) are typically sufficient for maintaining aerobic conditions
  • Containers: Sterile containers with tight-fitting lids are suitable for transporting specimens for aerobic culture

Anaerobic Transport

  • Anaerobic Transport Systems: Specialized systems designed to maintain an oxygen-free environment
    • Anaerobic Transport Vials: Contain a reducing agent (e.g., cysteine, thioglycolate) to remove oxygen and an indicator to confirm anaerobic conditions
    • Anaerobic Transport Bags: Oxygen-impermeable bags that can be sealed to create an anaerobic environment
  • Specimen Handling: Minimize exposure to air during collection and transport
    • Aspiration: Aspirate specimens from deep within wounds or abscesses to minimize exposure to oxygen
    • Inoculation: Inoculate anaerobic transport media immediately after collection
  • Examples of Anaerobes: Clostridium species, Bacteroides species, Peptostreptococcus species

Microaerophilic Transport

  • Specialized Transport Media: Some transport media are designed to provide a reduced oxygen environment
  • Gas-Generating Packets: Packets that generate a controlled atmosphere with reduced oxygen and increased carbon dioxide
  • Examples of Microaerophiles: Campylobacter species, Helicobacter pylori

Capnophilic Transport

  • Gas-Generating Packets: Packets that generate an atmosphere with increased carbon dioxide
  • Candle Extinction Jar: A simple method for creating a capnophilic atmosphere by placing a lit candle in a sealed jar. As the candle burns, it consumes oxygen and produces carbon dioxide
  • Examples of Capnophiles: Neisseria gonorrhoeae, Haemophilus influenzae, Streptococcus pneumoniae

Specific Considerations for Different Specimen Types

  • Wound Specimens: Deep wound specimens suspected of containing anaerobic bacteria should be transported in anaerobic transport systems
  • Genital Specimens: Specimens for Neisseria gonorrhoeae culture should be transported in a capnophilic environment to maintain viability
  • Gastrointestinal Specimens: Specimens for Campylobacter culture should be transported in a microaerophilic environment
  • Respiratory Specimens: Specimens for Streptococcus pneumoniae or Haemophilus influenzae culture may benefit from transport in a capnophilic environment

Common Errors and How to Avoid Them

  • Improper Use of Anaerobic Transport Systems: Follow the manufacturer’s instructions carefully to ensure that the anaerobic environment is maintained
  • Delay in Transport: Transport specimens to the laboratory as soon as possible to minimize the impact of atmospheric conditions
  • Exposure to Air: Minimize exposure of anaerobic specimens to air during collection and transport
  • Failure to Use Appropriate Transport Media: Select transport media that are appropriate for the organisms being tested for

Key Terms

  • Aerobic: Requiring the presence of oxygen for growth and survival
  • Anaerobic: Requiring the absence of oxygen for growth and survival
  • Facultative Anaerobic: Capable of growing in the presence or absence of oxygen
  • Microaerophilic: Requiring a reduced level of oxygen for growth
  • Capnophilic: Requiring an elevated level of carbon dioxide for growth
  • Transport System: A system used to maintain the viability and integrity of microorganisms during transport
  • Reducing Agent: A substance that removes oxygen from the environment
  • Gas-Generating Packet: A packet that generates a controlled atmosphere with specific gas concentrations