RODAC Plates: A Microbiological Monitoring

Microbiological Monitoring (RODAC Plates) in Pharmaceuticals

RODAC Plates full form is Replicate organism detection and counting

  • “Contact plates” is another name of Rodac Plates.
  • Rodac plates are a type of contact plate used in microbiology to collect and quantify microbial contamination on surfaces.
  • The name “Rodac” is derived from the manufacturer of these plates, RODAC International BV. These plates are also known as contact plates, surface plates, or paddle plates.
  • Rodac Plates or Contact Plates are used in pharmaceutical and other industries for surface sampling of micro-organisms and environmental monitoring.
  • By far the most used surface sampling equipment is RODAC plates.
  • They are agar contact plates with a 50 mm diameter (d) on which a dome-shaped layer of agar has been poured.
RODAC Plates- A Microbiological Monitoring
  • Micro-organisms will adhere when the agar media is put up against a flat surface.
  • Each plate samples about 3.99 square inches (, which is easily converted to the nos. of microbes per square inch.
  • It has been said that the effectiveness is comparable to quantitative swabs, which can recover between 10% and 50% of the substance that is truly present on a surface.
  • RODAC plates can be produced on-site or purchased commercially from a number of vendors.
  • The RODAC is extremely comparable to a device known as a Hycon contact plate, which is square in design and enclosed in a peel-open flexible plastic envelope.
Hycon plates
Credit @merck
  • The flexibility of Hycon plates gives them an edge over the inflexible RODAC plate.
  • Any surface that was touched after using a contact sampler needs to be cleaned and disinfected to get rid of any remaining agar.

RODAC Plates Types

There are several different growing medium for Rodac plates.

Mainly this three common varieties utilized for industrial cleaning applications:

  1. BPA (Baird Parker Agar) Type S (For determining the amount of Staphylococcus aureus).
    • Rodac type BPA full form is Baird Parker Agar.
    • Staphylococcus aureus, one of the most significant causes of infections of the internal organs as well as of the skin or wounds, is treated with BPA of the Rodac type.
    • It is also an undesirable bacterium in the food sector because it produces toxins that can cause food poisoning.
  2. Rodac type VRBGA (Violet Red Bile Glucose Agar) Type E (For determining the amount of Enterobacteriaceae)
    • Rodac type VRBGA full form is Violet Red Bile Glucose Agar
    • This Rodac type VRBGA used for potential Enterobacteriaceae existence.
    • Salmonella and Klebsiella are members of this bacterial family.
  3. Rodac type TSA (Tryptone Soya Agar) + Tween 80 + Lecithin : Type T (For determining the total amount of micro-organisms (general hygienic state)
    • Rodac type TSA full form is Tryptone Soya Agar combination with Tween 80 & Lecithin.
    • This type is eg described in the AFNOR (France), the recommendations of the Health Council (Belgium), RAL (Germany).
    • In comparison with the PCA (Plate Count Agar) TSA is (T.  S.  Agar) richer in nutrients and contains the Tween and Lecithin for the inactivation of inhibitory substances.

General Procedures for Microbiological Monitoring with RODAC Plates or How to use rodac plates ?

  • RODAC plates (Rodac type TSA) utilize Trypticase Soy Agar with Lecithin and Polysorbate 80.
  • After delivery, RODAC plates refrigerated and maintained upside-down.
  • When you’re ready to use anything, take the lid off and carefully touch the surface of the place or piece of equipment that needs sampling.
  • Replace the cover because airborne impurities can skew the results of the RODAC plate.
  • The plates should be warmed in the plastic sleeve to room temperature for roughly 15-20 minutes with the agar up and the lid down before sampling. Take out from the sleeve the number of plates needed for testing.
  • The plate’s base needs to be numbered, and the lid needs to be taped shut. It is necessary to keep a numbered list of the sampled locations that correspond to the exposed numbered plates.
  • Cleaned, sterilized, and dried the regions before placing the RODAC plate on the surface.
  • A sterile cotton-tipped swab is soaked with sterile water and rubbed over or inside of uneven surfaces for such surfaces.
  • The RODAC plate’s surface is next lightly scraped with the swab.
  • Sampling taken within two hours of cleaning and sanitizing.
  • By taking a sample from a soiled surface like the floor before washing and disinfecting it, one plate out of ten might be used as a positive control.
  • Bacteria and fungus should grow on this plate.
  • Facilitated Rodac Plates for 24 and 48 hr for counting of colonies.
  • RODAC plates will be incubated at 35°C (degrees Celsius) and observe the plates for growth at 24 and 48 hours. Any colonies will be counted at both time points.
  • Report the results.

Result of Sampling plate:

  • Results reported as follows for contact plates for environmental monitoring:
    • 0-5 colonies: None or very slight colonies (considered excellent)
    • 6-15 colonies: Slight (considered good)
    • 16-30 colonies: Moderate (borderline acceptable)
    • 31-50 colonies: Significant (poor)
    • >50 colonies: Heavy (unacceptable)
    • TNTC : Too Numerous to count (unacceptable)
  • With the exception of Plant facilities, each facility that needs testing will have its disinfection effectiveness checked at least twice a year.
  • Hood work surfaces, racks, walls, floors, cages, wire tops, and micro-isolator lids are a few examples of materials that needed to disinfect or sanitized according to the RODAC plate.
  • Some items that are either hand-washed or put through a home dishwasher of the standard RODAC type are water bottles, sipper tubes, and feed bowls.

Incubation of Rodac Plates:

  • The incubation period is 3-5 days at 30 to 35ºC. For additional incubation, the standard is 2 to 4 days at 20-25ºC after the initial 3-5 days at 30-35ºC.

Precaution or General Care during the use of Rodac Plates

  • The recommended storage temperature for RODAC plates is 40°F (2–8°C).
  • Avoid freezing, and limit your exposure to light
  • Storage of plates ideally done with the agar up and the lid down to reduce the chance of condensation-related contamination.
  • Wear gloves while you are performing a sampling.
  • Do not use expired plates

Brief Advantages and Disadvantages:

  • The advantages of using Rodac plates include their ease of use, relatively low cost, and ability to sample large surface areas. They can be used to sample irregularly shaped surfaces and can be easily transported to the laboratory for incubation and analysis. Additionally, the agar surface of the plate provides a large surface area for the growth of microorganisms, allowing for the detection of low levels of contamination.

  • However, there are also some limitations or disadvantages to the use of Rodac plates. The plates are not effective for the detection of all types of microorganisms, and the results obtained may be influenced by factors such as the pressure applied during sampling and the duration and temperature of incubation. Additionally, the agar surface may dry out during transport or storage, affecting the accuracy of the results. Therefore, it is important to follow proper sampling and incubation protocols and to interpret the results in the context of the specific application and environmental conditions.

Who are the Leading manufacturers of Rodac plates or sampling plates?

There are several manufacturers of Rodac plates in the market, including:

  1. Merck KGaA : Merck KGaA is a leading science and technology company that offers a wide range of products and services in the healthcare, life science, and performance materials sectors. Their Rodac plates are made of high-quality materials and are designed to meet the highest industry standards.
  2. 3M :3M is a global science company that provides innovative solutions for a range of industries, including healthcare, safety, and transportation. Their Rodac plates are made with advanced materials and are designed for ease of use and accuracy.
  3. Thermo Fisher Scientific : Thermo Fisher Scientific is a global leader in scientific research and laboratory equipment, offering a wide range of products and services for the healthcare and life science industries. Their Rodac plates are designed to provide reliable and accurate results in a variety of applications.
  4. Hardy Diagnostics : Hardy Diagnostics is a leading manufacturer of microbiology products, including culture media, stains, and reagents. Their Rodac plates are made with high-quality materials and are designed to meet the needs of microbiology laboratories.
  5. Bio-Rad Laboratories : Bio-Rad Laboratories is a global leader in life science research and diagnostics, offering a wide range of products and services for the healthcare and life science industries. Their Rodac plates are made with advanced materials and are designed for accuracy and ease of use.

These are just a few of the leading manufacturers of Rodac plates in the market. It is important to select a reputable manufacturer that meets industry standards and provides high-quality products for accurate and reliable results in microbiological testing.


  1. What does TSA stand for in microbiology:
    • Ans. TSA stand for Remel Tryptic Soy Agar, A solid medium called Remel Tryptic Soy Agar (TSA) is suggested for use in high-quality processes for the isolation and cultivation of a broad range of organisms.
  2. How does the Rodac Plates made?
    • Ans. Rodac plates are made of a sterile polystyrene dish with a flat bottom and a removable lid. The dish contains a layer of agar, which serves as a medium for the growth of microorganisms. The agar can be supplemented with nutrients to support the growth of specific types of microorganisms. The lid of the plate has a handle that is used to press the agar surface against the surface being sampled, allowing for the collection of microorganisms.


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