Amies Transport Medium – Composition, Principle, Preparation, Results, Uses

What is Amies Transport Medium?

• Amies Transport Medium is a specialized transport medium used for the transportation and preservation of microbiological specimens. It is a semi-solid, non-nutritive medium designed to maintain the viability of pathogenic organisms during transit from the collection site to the laboratory.
• The main purpose of a transport medium is to provide a suitable environment for the survival of microorganisms while inhibiting self-destructive enzymatic reactions and toxic oxidation reactions. Amies Transport Medium, developed by modifying Stuart’s Transport Medium, offers several advantages over the original formulation.
• One of the modifications in Amies Transport Medium is the replacement of glycerophosphate with an inorganic phosphate buffer. This alteration helps create a reduced environment within the medium, which is crucial for the survival of certain microorganisms. Additionally, a small amount of agar is included in the medium, which further contributes to its semi-solid consistency.
• Charcoal is another key component added to Amies Transport Medium. Charcoal serves the purpose of neutralizing materials that could be toxic to sensitive pathogens, such as Neisseria gonorrhoeae. By removing potential toxins, charcoal helps maintain the viability of these pathogens during transportation.
• The presence of calcium, magnesium, potassium, and sodium salts in Amies Transport Medium plays a role in promoting the survival of bacterial cells, particularly gonococcal cells. These salts also help regulate the permeability of bacterial cells.
• Phosphates are included in the medium to buffer its pH and maintain a stable environment during transportation.
• When collecting specimens for transport, it is recommended to use sterile cotton-tipped swabs or wooden sticks. The swab should be inserted one-third of the depth of the medium, and upon screwing the cap tightly, the swab is forced to the bottom of the medium. It is important to keep the medium cool during transportation but avoid freezing it, as extreme temperatures can affect the viability of the organisms.
• While Amies Transport Medium effectively preserves specimens during transportation, the viability of the organisms may diminish over time. Longer periods of transport can also lead to some growth of contaminants. Therefore, it is crucial to inoculate the specimen onto an appropriate culture medium as soon as possible after transportation to obtain optimum results. Ideally, the time lapse between sample collection and inoculation should be minimized.
• It is worth noting that cultures on transport swabs should not be kept at room temperature for more than 24 hours to prevent the risk of overgrowth or loss of viability.
• In summary, Amies Transport Medium is an improved transport medium containing charcoal, which enhances the viability of pathogenic organisms during transportation. It is a semi-solid, non-nutritive medium that provides a suitable environment for the survival of microorganisms while inhibiting self-destructive enzymatic reactions and toxic oxidation reactions.

Principle of Amies Transport Medium

The principle of Amies Transport Medium revolves around providing an optimal environment for the transport and preservation of sensitive pathogens such as Neisseria gonorrhoeae. This transport medium is designed to maintain the viability and integrity of the bacterial cells during transit from the collection site to the laboratory for further analysis.

Amies Transport Medium achieves this by incorporating several key components. Sodium thioglycollate and a small amount of agar are present in the medium to create a reduced environment. This reduction in oxygen availability helps to prevent the overgrowth of contaminants and maintain the viability of the target pathogens. The reduced environment is particularly important for the survival of anaerobic organisms.

The addition of charcoal in Amies Transport Medium plays a crucial role in neutralizing materials that may be toxic to sensitive pathogens like Neisseria gonorrhoeae. Charcoal acts as an adsorbent, binding and removing toxic substances that could potentially harm or inhibit the growth of the bacteria during transportation.

Furthermore, the medium contains calcium, magnesium, potassium, and sodium salts. These salts help to support the survival of gonococcal cells by providing essential nutrients and maintaining osmotic balance. They contribute to controlling the permeability of the bacterial cell membranes, which is important for protecting the cells from external stressors and preventing leakage of cellular contents.

Phosphates are also included in the medium as buffering agents. They help to maintain the pH of the medium within a suitable range, ensuring the stability of the bacterial cells during transportation. Proper pH control is crucial for preserving the viability of the pathogens and preventing potential damage caused by pH fluctuations.

In summary, the principle of Amies Transport Medium is to provide a reduced environment, neutralize toxic substances, supply essential nutrients, control permeability, and buffer the medium’s pH. By incorporating these components, Amies Transport Medium ensures the survival, integrity, and viability of sensitive pathogens like Neisseria gonorrhoeae during their transportation from the collection site to the laboratory for diagnostic purposes.

Composition of Amies Transport Medium

Ingredients	Gms/liter
Sodium chloride	3.000
Potassium chloride	0.200
Calcium chloride	0.100
Magnesium chloride	0.100
Monopotassium phosphate	0.200
Disodium phosphate	1.150
Sodium thioglycollate	1.000
Charcoal	10.000
Agar	4.000

Final pH (at 25°C) 7.2±0.2

Preparation of Amies Transport Medium

The following is a step-by-step guide on how to prepare Amies Transport Medium:

1. Start by measuring 20 grams of Amies agar and place it in a container.
2. Add 1 liter of distilled water to the container, ensuring that the agar is completely submerged.
3. Heat the mixture, bringing it to a boil. Continue heating until the agar is fully dissolved in the water.
4. While the mixture is still hot, carefully distribute it into small bottles with screw caps. Stir the mixture as you pour to keep the charcoal evenly suspended throughout the medium.
5. Once the bottles are filled, screw down the caps firmly to ensure a tight seal.
6. To sterilize the medium, place the bottles in an autoclave. Set the autoclave to a temperature of 121°C and a duration of 15 minutes. This process effectively kills any potential microorganisms present in the medium.
7. After autoclaving, invert the bottles while they cool. This helps distribute the charcoal uniformly throughout the medium.
8. Once cooled, store the bottles in a cool place until they are ready for use. It is important to maintain the sterility of the medium during storage.
9. When collecting a specimen, ensure that you are using sterile, cotton-tipped swabs attached to wooden sticks.
10. Carefully insert the swab into the Amies Transport Medium, pushing it down one-third of the depth of the medium.
11. Trim the wooden stick so that when the cap is screwed down, the swab is forced to the bottom of the medium, ensuring optimal contact.
12. Securely tighten the cap on the bottle to maintain the integrity of the medium during transportation.
13. Throughout the transport period, it is crucial to keep the bottle cool to preserve the viability of any microorganisms present in the specimen.

By following these steps, you can effectively prepare Amies Transport Medium for the collection and transportation of specimens in a microbiology laboratory or clinical setting.

Inoculation of the Medium

The Amies transport medium is commonly used in clinical settings for the transportation and preservation of various types of specimens, particularly those collected on sterile cotton wool swabs. The proper inoculation method is crucial to ensure the integrity of the specimen during transit and to maintain its viability for subsequent laboratory analysis. Here is a step-by-step guide on the inoculation method of the Amies transport medium:

1. Expiry Date Check: It is essential for clinics and ward staff to verify the expiry date of the Amies transport medium before using it. Expired mediums may not provide optimal conditions for specimen preservation and transportation.
2. Collection of Specimen: Using a sterile cotton wool swab, collect the specimen from the appropriate site or area of interest. The swab should be handled carefully to maintain sterility.
3. Immersion into the Medium: Immerse the cotton tip of the swab into the Amies transport medium. The swab stick should be cut off or broken to allow for the bottle top to be tightly replaced. This ensures a secure seal and prevents leakage during transportation.
4. Insertion into the Medium: Insert the swab into the medium with the cotton tip facing downwards. The swab should be inserted to approximately one-third of the depth of the medium. This depth ensures sufficient contact between the specimen and the medium for optimal preservation.
5. Adjusting the Swab Stick: If the swab stick is longer than the tube, it should be cut off or broken to fit properly. This adjustment ensures that the cap can be screwed on firmly without any obstruction.
6. Cap Tightening: Screw the cap of the Amies transport medium tightly. As the cap is tightened, the swab will be forced to the bottom of the medium, ensuring proper contact and immersion of the specimen.
7. Transportation: It is important to transport the specimen to the laboratory as soon as possible to minimize any potential degradation. Ideally, the transport should be completed within 6 hours. However, if necessary, the maximum time limit for transportation can be extended up to 24 hours. During transportation, it is crucial to maintain a cold chain, ensuring the medium remains chilled. However, it should not be frozen, as freezing may damage the specimen.

By following these guidelines for the inoculation method of the Amies transport medium, clinics and ward staff can effectively preserve and transport specimens for accurate laboratory analysis.

Result on Amies Transport Medium

Organisms	Growth
Escherichia coli	Good recovery on subculture
Klebsiella pneumoniae	Good recovery on subculture
Neisseria meningitidis	Good recovery on subculture
Pseudomonas aeruginosa	Good recovery on subculture
Salmonella Typhi	Good recovery on subculture
Shigella flexneri	Good recovery on subculture
Staphylococcus aureus subsp. aureus	Good recovery on subculture
Vibrio cholerae	Good recovery on subculture
Bacteroides fragilis	Good recovery on subculture
Haemophilus influenzae	Good recovery on subculture
Neisseria gonorrhoeae	Good recovery on subculture
Streptococcus pyogenes	Good recovery on subculture

Quality Control of Amies Transport Medium

Quality control of Amies Transport Medium is essential to ensure its effectiveness and reliability in preserving and transporting microbiological specimens. Here are some key aspects of quality control for this medium:

1. Appearance: Amies Transport Medium should have a grey to black homogeneous free-flowing powder appearance. Any deviation from this appearance could indicate a potential issue with the quality or stability of the medium.
2. Gelling: The medium should gel to a semisolid consistency comparable to a 0.4% Agar gel. This property is important as it contributes to the proper preservation and transportation of microorganisms.
3. Colour and Clarity of Prepared Medium: After preparation, the medium should form black-colored opaque gels in tubes. This visual characteristic is indicative of the correct formulation and successful gel formation.
4. Reaction: A 2% w/v aqueous solution of Amies Transport Medium should have a pH of 7.2 ± 0.2 at 25°C. This pH range ensures the medium’s compatibility with the growth and viability of microorganisms.
5. Cultural Response: Quality control involves assessing the cultural response of specific microorganisms when subcultured on Soybean Casein Digest Agar (M290) after incubation at 35-37°C for 18-24 hours. The expected luxuriant growth (50-100 CFU) of various organisms, such as Escherichia coli, Klebsiella pneumoniae, Neisseria meningitidis, Pseudomonas aeruginosa, Salmonella Typhi, Shigella flexneri, Staphylococcus aureus, and Vibrio cholerae, confirms the medium’s ability to support the growth of these organisms.
6. Storage and Shelf Life: Proper storage conditions are crucial to maintaining the quality of Amies Transport Medium. It should be stored between 10-30°C in a tightly closed container, while the prepared medium should be stored at 5-25°C. The product should be used before the expiry date indicated on the label to ensure optimal performance. Care should be taken to store the product in a dry, ventilated area protected from extreme temperatures and potential sources of ignition. Tightly capping the bottle after use is necessary to prevent lump formation due to the product’s hygroscopic nature.

By adhering to these quality control measures, laboratories can ensure that Amies Transport Medium is reliable, effective, and capable of preserving and transporting microbiological specimens accurately.

Uses of Amies Transport Medium

Amies Transport Medium is widely used for the collection, transportation, and preservation of various microbiological specimens. Its versatile applications make it an essential tool in the field of microbiology. Here are some key uses of Amies Transport Medium:

• Throat, Vaginal, and Wound Swab Samples: Amies Transport Medium is particularly suitable for collecting and preserving specimens obtained from the throat, vaginal, and wound areas. It provides a favorable environment for the survival and viability of microorganisms present in these samples during transportation to the laboratory.
• Sputum: When dealing with sputum specimens, a purulent part of the sputum can be transferred onto a cotton-wool swab and inserted into a container of Amies Transport Medium. This medium not only ensures the survival of pathogens such as Streptococcus pneumoniae and Haemophilus influenzae but also prevents the overgrowth of fast-multiplying commensal bacteria.
• Pus: For pus specimens, a sterile cotton-wool swab can be used to collect the sample. In cases where pus is not discharged, a sterile cotton swab can be used to obtain a sample directly from the infected site. The collected specimen is then inserted into a container of Amies Transport Medium. To ensure proper sealing, the swab stick should be broken off, allowing the bottle top to be tightly replaced.
• Nasopharyngeal Specimen: In order to identify carriers of Neisseria meningitidis, a nasopharyngeal swab specimen is collected and transported to the laboratory. Amies Transport Medium, along with Stuart’s medium, is commonly used for this purpose. Alternatively, the specimen can be directly plated onto a suitable medium and transported in a CO2-containing system. Amies Transport Medium also finds application in suspected cases of Bordetella pertussis and Corynebacterium diphtheriae.
• Urogenital Swab: Amies Transport Medium is considered the most efficient medium for transporting urethral, cervical, and vaginal swabs. It ensures the survival of delicate organisms such as Haemophilus ducreyi, which causes soft chancre, and Neisseria gonorrhoeae. The use of Amies Transport Medium in urogenital samples helps maintain the viability of these organisms during transportation to the laboratory.

Amies Transport Medium plays a crucial role in preserving the integrity and viability of microorganisms present in various specimen types during transportation. Its usage in different clinical settings facilitates accurate and reliable microbiological analysis, aiding in the diagnosis and treatment of infectious diseases.

Limitations of Amies Transport Medium

While Amies Transport Medium offers several advantages in the preservation and transportation of microbiological specimens, it is not without limitations. These limitations should be taken into consideration to ensure accurate and reliable results in diagnostic procedures. The following are some notable limitations of Amies Transport Medium:

• Freshness and Charcoal Resuspension: Before use, the medium requires careful handling. The old medium should be freshly steamed, and the charcoal present in the medium needs to be properly resuspended. Failure to follow these instructions can affect the performance of the medium and compromise the viability of the microorganisms.
• Contaminant Growth: During the extended period of transportation, there is a possibility of some growth of contaminants within the Amies Transport Medium. Contaminants can interfere with the analysis of the target microorganisms and potentially lead to false-positive or false-negative results. It is crucial to minimize the transportation time and handle the samples with care to minimize the risk of contamination.
• Timely Inoculation: After transportation, it is essential to transfer the specimen from the Amies Transport Medium to the appropriate culture medium as soon as possible. For optimum results, the time interval between sample collection and inoculation onto the culture medium should be minimized. Prolonged exposure to Amies Transport Medium may affect the viability and growth characteristics of the microorganisms, potentially leading to inaccurate results.
• Unsuitability for Fastidious Organisms: Amies Transport Medium may not be suitable for the transportation of fastidious organisms. Fastidious organisms have specific and often complex nutritional requirements for growth, and the non-nutritive nature of Amies Transport Medium may not provide adequate support for their viability during transportation. Alternative transport media specifically formulated for fastidious organisms should be considered in such cases.
• Decrease in Gonococci Viability: While Amies Transport Medium can support the survival of Neisseria gonorrhoeae (gonococci) for a limited period, the numbers of these bacteria decrease significantly after 24 hours of storage in the medium. If the initial specimen contains a low number of gonococci, their recovery may be compromised after this time frame, leading to potential false-negative results. Therefore, prompt analysis and inoculation onto appropriate culture media are crucial for accurate detection of gonococci.

To mitigate these limitations, it is important to carefully follow the manufacturer’s instructions for the preparation and use of Amies Transport Medium. Additionally, minimizing transportation time, handling samples with care, and considering alternative transport media for fastidious organisms can help ensure the accuracy and reliability of microbiological analysis and diagnosis.

FAQ

References

• https://exodocientifica.com.br/_technical-data/M651.pdf
• https://www.onlinebiologynotes.com/amies-transport-medium-composition-preparation-and-uses/
• https://microbiologie-clinique.com/antibiotic-susceptibility-testing.html
• https://microbeonline.com/amies-transport-medium/
• https://www.clinisciences.com/en/buy/cat-amies-medium-transport-media-for-5546.html
• https://assets.thermofisher.com/TFS-Assets/LSG/manuals/IFU60060.pdf