Transport media for microorganisms are essentially buffer solutions containing carbohydrates, peptones, and other nutrients (excluding growth factors) that are designed to keep bacteria alive during transport while preventing them from multiplying. The primary goal of using the transport medium is to keep the sample as close to its original state as possible.
What is Transport Media?
Transport media are basically buffer solutions with carbohydrate, peptones, and other nutritional elements (but not growing factors) that are meant to keep bacteria healthy during transport without letting them grow. The main goal of using the medium is to keep the sample as close as possible to how it was when it was first taken.
The objective of the transport medium is to safeguard the specimen and restrict bacterial overgrowth from the moment of collection to sample processing. Transport media might vary according to the types of organisms present in the sample.
In general, transport media are categorised according to the physical condition of their constituents, such as semi-solid or liquid, and their efficiency as viral or bacterial transport media.
Transport Media Components
Only salts and buffers are included. Contains no nutrients such as nitrogen, carbon, or organic growth stimulants, hence preventing the multiplication of microorganisms. Additionally, antibiotics and other chemicals such as glycerol could be employed to transport cultured tissues.
What samples are collected?
Every kind of sample may have pathogens but that cannot be processed in a timely manner need transport medium. It could be stool, urethral swabs throat and nasal swabs, and samples for tissue culture and so on.
Regularly used Transport media?
Here are a few instances of transportation mediums and their intended purpose:
- Cary and Blair Medium: Semi-solid colored transport material for human feces which could be contaminated with Salmonella, Shigella, Vibrio or Campylobacter.
- Amies medium with charcoal: Charcoal aids in the removal of metabolic substances produced by bacterial growth, which can be especially useful in identifying fastidious organisms. Other pathogens, such as Campylobacter, are recommended to be able to survive in this type of medium.
- Amies medium without charcoal: Ideal for isolation of Mycoplasma and Ureaplasma.
- Stuarts medium: Stuarts medium is commonly used to transport specimens suspected of containing gonococci. It is also used to transport swabs from wounds, throats, and skins that may contain pathogenic bacteria.
- Venkatraman Ramakrishnan (VR) medium: Venkatraman Ramakrishnan (VR) medium used to transport feces from suspected cholera patients.
- Sach’s buffered glycerol saline: Used to transport feces from patients suspected to be suffering from bacillary dysentery.
- Viral Transport Medium: The Viral Transport Medium (VTM) is ideal for detecting viral infections. This medium can be used to test ocular, respiratory, and tissue samples. Fluid samples, such as tracheal wash or peritoneal fluid, must be submitted in their original form in sterile vials to prevent desiccation. If no viral transport medium is available, place Swabs in sealed, sterile vials with a few drops saline to prevent desiccation. Wood-handled, plastic, cotton and dacron as well as other synthetic swabs are acceptable. Swabs made of calcium alginate should be avoided. The transport media of bacteria are not suitable for research in virology.
- Anaerobic Transport Medium (ATM): It is a mineral salt-based semi-solid media that contains reduction agents that are designed to be an absorbing medium to maintain the viability of anaerobic microbes. It is composed of buffered mineral salts in a semi-solid medium with cysteine and sodium thioglycolate as reducing agents to provide a safe environmental. Resazurin can also be used to act as a signal for redox in order to detect exposure to oxygen by changing to pink. It creates an atmosphere that ensures the viability of the majority of microorganisms, without massive multiplication, and permits reduction of inhibitors found in clinical materials. Examples include thioglycollate-based broth.