2.3 Transport Devices, Atmosphere, Time, and Temperature
Key Takeaways
- Match the device to the test: sterile cup, Amies/Stuart or flocked liquid-Amies swabs, anaerobic vials, blood-culture bottles, UTM/VTM, Cary-Blair for stool culture, and leakproof cups for AFB.
- Never refrigerate CSF, Neisseria gonorrhoeae, or anaerobic specimens destined for bacterial culture; blood-culture bottles also stay at room temperature.
- Refrigerate delayed urine, sputum, and C. difficile stool to limit overgrowth or toxin loss; use preservative systems (boric acid, PVA/formalin) when delay is expected.
- Atmosphere is part of transport: CO2/JEMBEC for gonococci and Haemophilus, microaerophilic conditions for Campylobacter, and oxygen-free vials for anaerobes.
- Shigella, N. gonorrhoeae, H. influenzae, and anaerobes are the classic fastidious losers when transport is dry, cold, delayed, or in the wrong medium.
2.3 Transport Devices, Atmosphere, Time, and Temperature
Quick Answer: Choose the device for the test, then protect atmosphere and temperature. Do not refrigerate CSF, gonococci, anaerobes, or blood-culture bottles. Do refrigerate delayed urine, sputum, and C. difficile stool. Cary-Blair is for stool culture; UTM is for viruses; anaerobic vials are for anaerobes.
Once the specimen is correctly identified and collected, it still has to survive the trip. Transport devices, atmosphere, time, and temperature finish outline I.A and remain inside the 10–15% Domain I weighting on the M(ASCP) exam. The typical item is a delayed specimen plus a fastidious organism: what dies, what overgrows, and which container would have prevented the false result. This is M bench knowledge, not SM-only laboratory administration.
Match the device to the test
A swab is not a universal transport. Fiber, medium, and oxygen exposure all change recovery.
| Device | Use it for | Do not use it for |
|---|---|---|
| Sterile leakproof cup | Urine, sputum, stool, tissue, AFB sputum | Prolonged unpreserved urine at room temp; anaerobic recovery from an air-filled cup |
| Amies or Stuart swab (often with charcoal) | Many routine bacterial swabs; charcoal Amies for suspected gonococci if plating will be prompt | Viral PCR (use UTM); C. difficile; AFB; anaerobic culture of a dry swab |
| Flocked swab in liquid Amies (ESwab-type) | Routine bacterial culture, Gram stain from the same tube | Specimens that need immediate anaerobic atmosphere or viral UTM chemistry |
| Anaerobic transport vial / gassed tube / PRAS | Tissue, aspirates, and swabs kept anaerobic | Leaving the cap off; refrigerating the vial; a dry aerobic swab "for anaerobes too" |
| Blood-culture bottles | Direct inoculation of blood (sometimes sterile fluids per SOP) | Refrigeration; pouring leftover blood into a cup "for later" |
| Viral / universal transport medium (VTM/UTM) | Viruses, many molecular respiratory/genital panels | Bacterial stool culture; AFB smear as the primary container |
| Cary-Blair | Stool bacterial culture (Salmonella, Shigella, Campylobacter, STEC culture) | C. difficile toxin/NAAT as the default (many assays reject preserved stool); O&P morphology |
| O&P preservative (PVA, formalin, total-fix) | Parasite microscopy after delay | Bacterial stool culture or C. difficile |
| AFB leakproof cup (5–10 mL sputum) | Mycobacteria smear/culture | A dried swab of "possible TB" |
Cotton swabs can be inhibitory (fatty acids) and hold less specimen than flocked nylon. Wooden shafts can be toxic to some fastidious organisms. If the order is N. gonorrhoeae culture, Dacron/rayon/flocked plus charcoal Amies or direct inoculation of warmed selective media (modified Thayer-Martin, JEMBEC plate with CO2 tablet) beats a dry cotton swab in a drawer.
Atmosphere is a transport variable
- Aerobic. Most routine wound, urine, and sputum pathogens tolerate room air if the specimen does not dry out. Pseudomonas and enteric gram-negatives are not the problem; drying and delay are.
- Capnophilic (about 5–10% CO2). N. gonorrhoeae, N. meningitidis, H. influenzae, S. pneumoniae, and Capnocytophaga need CO2 for isolation. JEMBEC plates, candle jars, and CO2 incubators exist because a capped aerobic swab in a truck does not generate that atmosphere.
- Microaerophilic. Campylobacter jejuni (typically 42°C, reduced oxygen) and Helicobacter pylori require a low-oxygen, CO2-enriched mix. A stool left in an ordinary cup will not preserve Campylobacter as well as Cary-Blair plus prompt microaerophilic setup.
- Anaerobic. Bacteroides, Clostridium, Fusobacterium, Prevotella, Porphyromonas, and Cutibacterium die after oxygen exposure. Tissue in an anaerobic vial at room temperature is the collection. Refrigeration increases oxygen dissolution and is the wrong instinct. A surface swab held in air is an aerobic culture, whatever the order says.
Blood-culture bottles already define atmosphere: aerobic and anaerobic bottles are inoculated at the bedside. Do not vent an anaerobic bottle. Do not refrigerate bottles "until the day shift loads the instrument." Hold them at room temperature and get them on the incubator.
Time and temperature: the exam's favorite table
There is no single refrigerator rule. Cold protects some specimens and kills others.
| Specimen / test | Temperature | Time pressure | Why |
|---|---|---|---|
| CSF, bacterial culture | Room temperature; process immediately | Minutes, not a next-morning stack | N. meningitidis, H. influenzae, and S. pneumoniae are cold-sensitive and autolytic |
| Blood-culture bottles | Room temperature | Load as soon as received | Cold and delay both reduce recovery; never refrigerate bottles |
| Urine, unpreserved | Refrigerate (2–8°C) if delay >2 hours | Or use boric-acid preservative ~24 h | Room-temp urine overgrows; colony counts become fiction |
| Sputum, routine bacteria | Refrigerate if delay | Hours, not overnight on a counter | Oral flora overgrow; pneumococcus dies |
| Stool culture | Cary-Blair; RT or fridge per SOP | Same day preferred | Shigella dies in acid unpreserved stool |
| C. difficile | Unformed stool in a clean cup; refrigerate if delayed | Toxin assays are especially time-sensitive | Toxin degrades at room temperature; do not incubate the cup |
| O&P | Preservative, then RT | Immediate if a fresh trophozoite wet mount is requested | PVA/formalin is not interchangeable with Cary-Blair |
| N. gonorrhoeae culture | Never refrigerate | Plate ASAP, CO2 | Cold, drying, and delay cause false-negative cultures |
| Anaerobes | Room temperature in anaerobic transport | Prompt setup | Fridge and air both kill |
| Viral NAAT/culture | UTM, refrigerate; freeze for long delay | 48–72 h refrigerated is a common window | Dry swabs and RT delay lose RNA viruses |
| AFB sputum | Refrigerate | Daily specimens ×3 still valid if held correctly | Overgrowth of routine bacteria is the enemy |
Never refrigerate CSF for bacterial culture. That sentence is worth a full exam item by itself. Viral PCR on leftover CSF can be refrigerated or frozen after the bacterial workup is protected, following the SOP; you do not freeze the only tube before plating. A 45-minute-old CSF that arrives in a cool pack should be set up immediately, not stored colder "to be safe."
Stool is not one specimen. C. difficile (unformed, refrigerated if delayed, often rejected if preserved) is not O&P (preservative) and is not enteric culture (Cary-Blair). Mixing those three on one delayed cup produces the wrong reject/accept decision.
Delayed transport: overgrowth versus death
Delay does two opposite things, and the M exam expects you to know which one applies.
Overgrowth (false or inflated positives, mixed flora that buries the pathogen):
- Unpreserved urine at room temperature: colony counts climb; periurethral mixed flora looks like a complicated UTI.
- Sputum on the counter: oral gram-negatives and yeast overgrow; the pneumococcus that actually caused pneumonia may already be dead.
- Unpreserved stool: coliforms overgrow Shigella and Salmonella.
Death (false negatives of fastidious pathogens):
- N. gonorrhoeae: drying, cold, delay, cotton swabs, missing CO2.
- H. influenzae: delay off chocolate/CO2, cold CSF or respiratory specimens.
- Anaerobes: oxygen, dry swabs, refrigeration.
- Shigella: acid pH of raw stool, delay without Cary-Blair.
- S. pneumoniae in CSF: autolysis plus cold.
- C. difficile toxin: room-temperature degradation (the organism's spores are hardy; the toxin protein is not). NAAT is more robust than toxin EIA but delayed RT stool is still the wrong storage.
If transport will exceed the unpreserved window, change the device, not the story. Boric acid for urine, Cary-Blair for enteric culture, UTM on ice packs for viruses, anaerobic vials for tissue, and a JEMBEC plate for gonococci are how laboratories buy time. Hoping the courier is fast is not a transport system.
Fastidious organisms the outline expects you to protect
Neisseria gonorrhoeae. Direct plate to selective media in CO2 whenever possible. If a swab must move, use Amies with charcoal, keep it at room temperature, and plate the same day. Overnight refrigeration of a cervical swab in aerobic Stuart medium is a designed false-negative. Cotton is a poor fiber choice.
Haemophilus influenzae. Chocolate agar and CO2, prompt processing of sputum, CSF, and ear drainage. It will not wait in a refrigerated CSF tube for the morning board.
Anaerobes. Tissue or aspirate in an anaerobic transport system, room temperature, processed without a long aerobic hold on the bench. A "wound swab for aerobes and anaerobes" in one dry tube is an aerobic culture only.
Shigella. Buffered transport (Cary-Blair), prompt plating to selective enteric media. Unpreserved, delayed, or frozen stool is how Shigella disappears while E. coli flourishes.
AFB containers look boring next to those four, but they still matter: a leakproof cup with adequate volume, refrigerated if delayed, never a dried swab labeled "rule out TB." Viral UTM is refrigerated, not left in a hot courier car, and is not a substitute for bacterial transport media.
CSF for bacterial culture arrives 45 minutes after lumbar puncture in a refrigerated specimen bag. The tube is still labeled and the volume is adequate. The correct bench action is:
Unformed stool for Clostridioides difficile testing cannot be assayed for 6 hours. How should it be stored?
A cervical swab for Neisseria gonorrhoeae culture is collected on a cotton swab, placed in aerobic Stuart transport, and refrigerated overnight before plating. The most likely result is: