Amies Transport Media Definition
Amies Transport Media is a common and effective way to get swab samples to the microbiology lab. It is a semisolid medium, Amies is a modification of stuarts media. Putting swabs in a moist container or other way to transport them keeps bacteria from drying out and dying.
Most common transport medium examples is Amies media is a modification of stuarts medium in which glycerophosphate is replaced by an inorganic phosphate buffer and charcoal is added. Stuart transport medium used for transport and preservation of microbiological specimens. Anaerobic bacterial pathogens, such as Neisseria gonorrhoeae, Haemophilus influenzae, Neisseria meningitidis, and Haemophilus ducreyi can now be more easily isolated with this change. Amies media with charcoal can be used for delays of up to 24 hours.
Amies Transport Medium Principle
Sodium thioglycollate and a small amount of agar create a low-oxygen environment that is good for the growth of a wide range of pathogens. When charcoal is used as a transport medium, it neutralises toxic materials in the sample or on the swab and makes it easier for sensitive bacterial pathogens like Neisseria gonorrhoeae to grow. Calcium, magnesium, potassium, and sodium salts help pathogens stay alive and also control how open bacterial cells are. Phosphate buffer keeps the pH of the medium stable.
Figure 1: Amies transport medium with charcoal.
Composition of Amies Transport Media
Final pH (at 25°C) 7.2±0.2
Preparation of Amies Transport Medium
Amies transport media is best made from dehydrated powder that is already ready to use and can be bought from most places that sell culture media. Amies transport medium preparation
- Put the amount of media you want to use in distilled water (2 grams in every 100 ml of distilled water)
- Bring to a boil to completely dissolve the medium.
- Pour 6-7 ml into screw-cap tubes or Bijou bottles that hold 10 ml.
- Sterilize by putting the bottles in an autoclave at 15 pounds of pressure (121°C) for 15 minutes with bottle caps loosened.
- Once the medium has cooled down, screw the bottle caps back on.
- While the agar is setting, turn the tubes over several times to keep the charcoal particles in a uniform suspension.
- Label the tubes with a lot number, the date they were made, and the date they will go bad (9 months from preparation).
- Keep the medium in a cool, dark place with the bottle tops tightly screwed on.
pH of medium: This should be within the range of pH 7.0-7.4 at room temperature.
Shelf-life: Up to 9 months providing there is no change in the volume or appearance of the medium to suggest contamination or an alteration of its pH.
Inoculation of Amies Transport Medium
Before using the medium, clinics and ward staff should be told to check the expiration date. Samples should be put into the medium using a sterile cotton wool swab. The swab stick should be cut off so that the bottle top can be put back on tightly.
- Put the cotton end of the swab into the medium until it is one-third of the way down.
- If the swab stick is longer than the tube, cut it off or break it.
- Tighten the cap so that the swab falls to the bottom of the medium.
- Maintain a cold chain and get the sample to the lab as soon as possible, preferably within 6 hours but no more than 24 hours (do not freeze).
Uses of Amies Transport Medium
Amies transport medium is used to collect, move, and store microbiological samples, like swabs from the throat, vaginal area, and wounds. It is often used to move samples from collection centres (or health centres) to the microbiology lab.
- Sputum: Transfer a purulent portion of the sputum on a cotton-wool swab, then place it in a container containing Amies transport medium. Amies medium enables the survival of pathogens like S.pneumoniae and H. influenzae while preventing the overgrowth of rapidly proliferating commensals.
- Pus: Collect a sample of pus using a sterile cotton swab. Use a sterile cotton swab to take a sample from the affected area if pus is not exuding. Insert it into a container of Amies transport medium, cutting off the swab stick in order to reinstall the bottle cap securely.
- Nasopharyngeal specimen: To detect N.meningitidis carriers, a nasopharyngeal swab is obtained and brought to the laboratory in Amies or Stuart’s medium, or plated directly onto medium and transported in a CO2-containing system. Additionally, Amies medium is utilised in suspected instances of Bordetella pertussis and Corynebacterium diphtheriae.
- Urogenital swab: Amies medium is the most efficient medium for transporting urethral, cervical, and vaginal swabs. It ensures the survival of Haemophilus ducreyi (which causes soft chancre) and delicate organisms like Neisseria gonorrhoeae.
Limitations of Amies transport medium
- Before usage of Amies transport media, the old medium should be newly heated and the charcoal should be resuspended.
- During the lengthy transport period, some development of pollutants may also occur.
- As soon as possible after travel, the specimen should be injected in the appropriate medium. Minimum time should elapse between sample collection and inoculation into culture medium for optimal results.
- It might not be ideal for transporting delicate organisms.
- Gonococci can live in Amies Transport Medium for at least 6 to 12 hours if not subjected to high temperatures. By 24 hours, the amount of gonococci in a specimen decreases to an extent that may impede their recovery if initially present in tiny numbers.