Types of Microbiology Transport Media: A Comprehensive Guide
- Microbiology transport media in are critical for maintaining the viability and integrity of clinical specimens during transit from the collection site to the laboratory. Different transport media are designed to cater to specific types of microorganisms and clinical applications.
- Recognise that all biological specimens are potentially hazardous and infectious.
- Ensure that the exterior of containers remains uncontaminated by specimens.
- Use adequate absorbent materials to prevent leakage or spillage during transit to the reference laboratory.
- Utilize leak-proof and durable containers for specimens; plastic containers are preferred.
- Deliver specimens promptly to the laboratory to ensure accurate results.
- Some culture specimens may require specific transport media (refer to TRANSPORT MEDIA section).
- If there’s a delay in transporting specimens to the laboratory, refrigerate or incubate as needed (37°C).
- Always include a properly filled request form with specimens to guide pathologists in selection of techniques or media.
SPECIMEN DISPATCH WITHIN THE LABORATORY:
- Match containers with respective request forms, assign numbers, record in dispatch register/computer, and verify during handover to laboratory departments.
- Notify relevant departments about urgent or specialized tests.
- Inform pathologists about important specimens.
TRANSPORT MEDIA:
While transport media are useful, processing clinical material immediately after collection is preferable. Various systems counter desiccation and inhibit substances in swabs or specimens. It’s essential to use transport or holding media when there’s a delay in transport to the laboratory. These can be commercial or prepared in-house, as described below:
1. CARY-BLAIR TRANSPORT MEDIUM
| Sodium thioglycollate | 0.75 g |
| Disodium hydrogen phosphate Na2HPO4) | 0.55 g |
| Sodium chloride | 2.5 g |
| Agar | 2.5 g |
| Calcium chloride 10g/L (1% w/v) | 4.5 ml |
| Water | 495 ml |
- Dissolve dry ingredients through heating.
- Cool to 50°C and add freshly prepared calcium chloride solution.
- Adjust pH to 8.4 using 0.1 M (N/10) NaOH.
- Dispense 7 ml into 9 ml screw cap bottles.
- Sterilize by steaming for 15 minutes.
- Shelf life: 6 months.
Uses: Preserves enteric pathogens, suitable for Yersinia pestis (Plague bacillus).
2. AMIES TRANSPORT MEDIUM
| Charcoal Pharmaceutical, neutral | 10.0 g |
| Sodium chloride | 3.0 g |
| Sodium hydrogen phosphate | 1.15 g |
| Potassium dihydrogen Phosphate | 0.2 g |
| Sodium thioglycollate | 1.0 g |
| Calcium chloride | 0.1 g |
| Agar | 0.1 g |
| D/Water | 4.0 g |
| Magnesium chloride | 0.1 g |
- Dispense mixed medium into screw-capped Bijou bottles.
- Autoclave at 121°C for 15 minutes.
Shelf life: 9 months
Uses: Transport for specimens suspected to have anaerobes, urethral/genital area specimens, and sputum.
3- STUART TRANSPORT MEDIUM
| Sodium glycerophosphate | 10 g |
| Sodium thioglycollate | 0.5 g |
| Cysteine hydrochloride | 0.5 g |
| Calcium chloride | 0.1 g |
| Methylene Blue | 0.001 g |
| Agar | 5.0 g |
| D/Water | 1000ml |
- Stir well the ingredients and fill small Bijou bottles.
- Sterilize at 121°C for 15 minutes.
Uses: Transport for urethral/genital specimens, sputum, throat swabs for Corynebacterium diphtheriae and S.pyogenes.
4. GLYCEROL SALINE TRANSPORT MEDIUM
| Sodium chloride | 4.2 g |
| Disodium hydrogen phosphate (anhydrous) | 3.1 g |
| Phenol Red 1% (w/v) | 0.3 ml |
| Glycerol | 300 ml |
| D/Water | 700 ml |
| Potassium dihydrogen phosphate | 1.0 g |
- Dissolve dry chemicals, adjust pH to 7.2.
- Add phenol red solution and glycerol, dispense into screw-capped bottles.
- Sterilize at 121°C for 15 minutes.
Shelf life: 2 – 8°C for 2 years.
Uses: Preserves enteric pathogens (Salmonellae, Shigellae, E.coli), not suitable for V.cholerae, Campylobacter sp, Y.enterocolitica.
5. ALKALINE PEPTONE WATER
| Sodium chloride | 5 g |
| D/water | 500 ml |
| Peptone | 5 g |
- Dissolve peptone and sodium chloride; adjust pH to 8.6-9.0.
- Dispense in 10 ml screw-capped bottles.
- Sterilize at 121°C for 15 minutes.
Shelf life: 2 – 8°C 2 years.
Uses: Transport for fecal specimens for V.cholerae and other vibrios.
6. VIRAL TRANSPORT MEDIUM
| Hank’s balanced salt solutionHank’s balanced salt solution | 43.0 ml |
| Bovine albumin 100g/L (10% w/v) | 5.0 ml |
| Phenol Red 4g/L (0.4% w/v) | 0.25 ml |
| Nystatin (2500 lU/ml in sterile PBS1) | 0.5 ml |
| Penicillin (104 lU/ml and Streptomycin 10mg/ml in sterile PBS) | 0.5 ml |
- Add sterile bovine albumin, phenol red, nystatin, penicillin, and streptomycin to Hank’s balanced salt solution.
- Adjust pH to 7.0.
- Dispense into sterile screw-capped bottles.
Uses: Various viral specimens for culture can be sent in this medium
7. BORDETELLA TRANSPORT MEDIUM
| Sterile sheep or horse blood | 10 ml |
| Cephalexin (40 mg/L) | 0.4 ml |
- Prepare and sterilize charcoal agar (half strength). Transfer to a 50°C waterbath.
- Add sterile blood, antibiotic solution, avoiding foam.
- Dispense in sterile 5 ml Bijou bottles.
Shelf life: 8 weeks at 2-8°C.
8. SUCROSE BUFFER FOR CHLAMYDIAE INFECTION
Stock Solution
| Ingredient | Amount | Water |
| Sucrose | 68.5 g | 100 ml |
| Dipotassium hydrogen phosphate (K2HPO4) | 2.1 g | 60ml |
| Potassium dihydrogen phosphate (KH2PO4) | 1.1 g | 40ml |
- Mix all the three solutions and make volume to one litre with distilled water. Boil for 30 min. Cool to room temperature.
Working Solution:
- In 100 ml stock solution, add 10 ml foetal calf serum, 2 mg Gentamicin powder, 0.5mg Amphotericin B powder and 10 mg Vancomycin.
- Dispense in 1 ml amount into sterile screw capped plastic disposable test tubes.
9. Universal Transport Medium (UTM):
- Composition: UTM contains a buffered saline solution with antimicrobial agents (like colistin and amphotericin B).
- Use: UTM is versatile and can be used for collecting and transporting various pathogens, including bacteria, viruses, and fungi.
10. Pneumococcal Transport Medium:
- Composition: This medium often contains skim milk or glycerol, along with other components.
- Use: It is specifically designed for the transport of specimens for the detection of Streptococcus pneumoniae, a common respiratory pathogen.
11. Amniotic Fluid Transport Medium:
- Composition: Amniotic fluid transport medium typically includes a buffered solution.
- Use: It is used for the collection and transport of amniotic fluid samples, especially for prenatal diagnostic purposes.
12. Modified Stuart Transport Medium:
- Composition: Similar to Stuart medium, but often with additional antimicrobial agents.
- Use: This medium is used for various clinical specimens when bacterial culture is required, and added antimicrobials help inhibit overgrowth of contaminants.
The choice of transport medium depends on the type of microorganisms being transported, the specific diagnostic requirements, and the conditions under which the specimen will be transported. Proper collection and preservation of clinical specimens are crucial for accurate and reliable microbiological analysis.
