Each lot of Hardy Diagnostics commercially manufactured media is processed and tested as indicted below unless otherwise noted on the product's Instructions for Use (IFU) or Certificate of Analysis (CofA). Lots are tested using appropriate quality control organisms and specifications in accordance with regulatory recommendations, where applicable.


All units of a particular batch are held in quarantine while representative samples are tested by the QC Department. No units in this area are released for sale until testing indicates reliability of the lot. If the lot fails the testing procedure for any quality control specification, it is documented in the records and the lot is discarded.


Each lot is examined for proper color, consistency, smoothness, lack of bubbles, lack of precipitates, lack of hemolysis, gel strength of agar, proper amount of fill, adequate depth, or slant configuration, as applicable. Some types of media may exhibit slight precipitation due to formulation that will disappear upon incubation at 35°C. (e.g. Thioglycollate Media, HE Agar, XLD Agar, etc.). Production equipment is monitored to ensure a consistent depth of media within the product tolerance specifications in all portions of the petri dish, tube, flask, or bottle. Media depth is of particular importance with susceptibility testing media such as Mueller Hinton Agar (Cat. no. H11).

The user should perform a visual inspection of all incoming shipments of media; checking for the following deficiencies:

  1. Cracked or damaged plates
  2. Agar detached from petri dishes
  3. Frozen or melted agar
  4. Unequal filling of plates
  5. Insufficient agar in the plates (< 3mm depth)
  6. Hemolysis of blood containing media
  7. Change in the expected color of the media (possible pH problem)
  8. Excessive bubbles or rough surfaces
  9. Excessive moisture or dehydration
  10. Obvious contamination
  11. Presence of precipitates

 If any problems are noticed in the visual inspection, immediately notify the Technical Support Department at (800) 266-2222 ext. 5598 or on our website.


Plated media is examined for intact bags, and for the absence of excessive moisture. Tube, flask, and bottle media are inspected for cap tightness. All products are checked at three different stages of production for accurate labeling information. Each container label may include:

  1. product name and catalog number
  2. lot number
  3. brief description of intended use
  4. expiration date
  5. plate or tube size
  6. number of units per container
  7. storage instructions
  8. fill


Samples of each lot are tested immediately after manufacture at room temperature (25°C) to ensure the lot is within the proper pH range. A routinely calibrated pH meter is used to test lots of finished product. Solid media is brought to room temperature, a glass surface electrode is applied to the surface, and sufficient time is allowed for equilibration (usually 1 to 5 minutes). The reading should be within 0.2 units of the stated pH (within 0.1 units for Mueller Hinton Agar).


A representative number of sample units are taken from the beginning, middle, and end of each production run. Sample units are evaluated based upon lot size using an American National Standards Institute/American Society for Quality statistical sampling plan (ANSI/ASQ Z1.4-2008). In general, the number of sampling units using the Acceptance Quality Limit (AQL) are as follows:

Batch size in units

Sample size in units





















A portion of lot samples are incubated at 35°C for seven days; two units are incubated at room temperature for seven days as a check for fungi or psychrophiles (organisms preferring cooler temperatures). Culture media intended for sterility testing by USP <71> methods is incubated for 14 days.

Certain media can be released for distribution if samples from the lot are free of contamination after 48 hours and the lot has passed routine performance testing; samples for microbial load testing will continue to be held for a total of seven days. Customers will be notified immediately if any contamination is observed during the remainder of the seven day incubation period. This is done to ensure fresh media with a long outdate. Products such as Dilu-Lok™ Butterfield's Phosphate and Butterfield's Phosphate with Magnesium Chloride are tested for sterility according to USP test methods using a Millipore Steritest™ membrane filtration system, and lots are released if samples are acceptable after 10 days.

Non-nutritive products such as Water with Tween® 80 and Saline are inoculated (1ml) into Tryptic Soy Broth and incubated at 35°C for seven days.

Unless otherwise noted, most culture media is not considered a "sterile" product, but will have a sterility assurance level (SAL) based upon the manufacturing process. Most culture media is not packaged under sterile conditions, and the packaging material is not sterile. However, the media has been autoclaved or filter sterilized and is produced in an environmentally controlled area (ECA) using high-efficiency particulate arrestance (HEPA) filtration and positive air pressure to minimize the chance of airborne contamination. Media that has been irradiated has a higher SAL than standard aseptically processed media, because the internal packaging of these products has also been irradiated.

Testing for contamination should be performed on media that is not exempt from QC. When testing for microbial load (contamination) it is advisable for the user to take a representative sample from each lot number of a particular shipment. 


Culture media will sometimes contain dead organisms that will be evident on a gram stain. Other sources of non-viable organisms include slides, staining reagents, immersion oil, or the original specimen.

For some culture media it is recommended that biochemical, immunological, molecular, or mass spectrometry testing be performed on colonies from pure culture for complete identification.

Organisms differ in their requirements for humidity, temperature, atmosphere (levels of oxygen), and duration of incubation. These requirements must be observed in order to successfully culture the desired organism. Refer to the document "Inoculation Procedures for Media QC" on the Hardy Diagnostics Technical Document website for more information.

Selective media may at times permit certain strains of organisms to grow that are intended to be inhibited; conversely, certain strains may be inhibited that are intended to grow. It is therefore advisable to use a nonselective medium in parallel with a selective one to increase the chances of recovery of a pathogen.

Other variations of intended results may be due to improper specimen collection and transport, improper execution of procedures, improper exposure to temperatures or atmospheres, strain mutation or variation, or interference from other chemicals or inhibitors.


The Instructions for Use (IFU) and Certificates of Analysis (CofA) for each product describe in detail the performance specifications utilized by Hardy Diagnostics. Instructions for Use are located under the Online Catalog or on the Hardy Diagnostics Technical Document website. Certificates of Analysis can be found using the product and lot number on the Hardy Diagnostics Certificates of Analysis website. 

Hardy Diagnostics makes no recommendations explicit or implied as to the amount or extent of quality control testing that should be performed by the user laboratory. End users of commercially prepared culture media should perform QC testing in accordance with applicable government regulatory agencies, and in compliance with accreditation requirements. Hardy Diagnostics recommends end users check for signs of contamination and deterioration and, if dictated by laboratory quality control procedures or regulation, perform quality control testing to demonstrate growth or a positive reaction and to demonstrate inhibition or a negative reaction, if applicable. Hardy Diagnostics quality control testing is documented on the Certificates of Analysis (CofA) available from Hardy Diagnostics Certificates of Analysis website. In addition, refer to the following document on the Hardy Diagnostics Technical Document website for more information on QC: "Introduction to Quality Control.”

Representative samples of this lot were tested and found to meet the specifications listed on this certificate and published in "Technical Documents and IFUs" under the "Technical Support" menu item located at, where applicable. In addition, this lot conforms to the quality control standards listed in the reference document, when indicated. End users of commercially prepared culture media and reagents should perform QC testing in accordance with applicable government regulatory agencies, and in compliance with accreditation requirements. Hardy Diagnostics recommends end users check for signs of contamination and deterioration and, if dictated by laboratory quality control procedures or regulation, perform quality control testing to demonstrate a positive reaction and/or a negative reaction, if applicable.


American Type Culture Collection (ATCC®) derived strains are utilized as recommended by ATCC and in accordance with CLSI recommendations, where applicable.

Organisms are obtained in a lyophilized or preserved form from the following sources:

  1. Microbiologics, St. Cloud, MN
  2. American Type Culture Collection (ATCC®), Rockville, MD

All organisms from the above sources are derived from ATCC® reference strains. When required, additional clinical isolates provided by our customers are used on occasion.

A complete list of stock organisms manufactured by Microbiologics is available to customers through Hardy Diagnostics. See the Online Catalog at


CLSI requires stock cultures be started from a lyophilized pellet or a frozen culture. Lyophilized cultures are reconstituted by placing the pellet in a tube of 0.5ml of TSB or BHI Broth. A swab is then inserted into the broth to crush the pellet. The same swab is used to immediately inoculate a Blood Agar or Chocolate Agar plate. Other appropriate solid media may be used if they do not contain antibiotics or any other inhibitory substances. Positive control organisms with plasmid-mediated resistance mechansisms may require subsequent culture and maintenance on selective media, as indicated.

Please note: successful reconstitution requires the organism be initially cultured on a solid medium with a wide surface area to obtain isolated colonies and to check for purity. Never attempt to cultivate a lyophilized or frozen organism in a broth. Also, never reconstitute on a medium that contains antibiotics or any other inhibitory substance, unless otherwise indicated by ATCC® or the manufacturer's instructions.

Plates are then incubated at an appropriate atmosphere and temperature for the required duration. When culturing anaerobes and Campylobacter spp., using jars with gas generating envelopes is significantly more reliable than bag systems for the regeneration of lyophilized microorganisms. Allow initial anaerobic and microaerophilic pellet cultures to incubate for the full incubation period before exposing them to ambient air to reduce the chance of damaging sensitive cells.


Frozen cultures can be stored at -50°C for up to one year. Cultures may be kept indefinitely at -70°C or colder. Freezing in a frost-free or household freezer (-20°C) is not recommended.

Hardy Diagnostics CryoSavers™ are ideal for long-term storage of frozen cultures. This product line consists of a polypropylene vial containing a cryopreservative broth (Brucella Broth with 10% Glycerol or Skim Milk Broth) and comes with or without beads.


CLSI recommends 'Stock Controls' be prepared at least once per year from lyophilized or frozen cultures. Secondary or 'Working' cultures can be stored on an agar slant at room temperature or at 2-8°C for up to four weeks. After four weeks, a new 'Working' culture is prepared from the 'Stock Control.'

Cultures used for the quality control of disk diffusion susceptibility testing should be stored on TSA (Soybean-Casein Digest Agar) slants at 2-8°C and 'Working' cultures subcultured weekly for no more than three weeks. New 'Stock' cultures should be prepared at least monthly from frozen, freeze-dried, or commercial sources.


Various media inoculation methods are listed under "Inoculation Procedures for Media QC" on the Hardy Diagnostics Technical Document website. These methods correspond to the specific type of media in each product's Instructions for Use (IFU) on the Hardy Diagnostics Technical Document website.

Procedures for susceptibility media, such as Mueller Hinton Agar, can be found under "Inoculation Procedures for Media QC", Method F. Quality control interpretive criteria (zone sizes) for antimicrobial susceptibility disks can be found in the current CLSI M100, Performance Standards for Antimicrobial Susceptibility Testing, document available through


After inoculation and incubation, quality control performance results are recorded and maintained along with the lot's records. A particular lot of media is released from the quarantine area for distribution when it meets the following criteria:

  1. Test strains show satisfactory growth with typical colony morphology on nutritive media.
  2. Test strains show satisfactory inhibition, when appropriate, on selective media.
  3. Biochemical tests show typical results when tested for a positive and negative reaction.
  4. Culture media is found to be free of contamination.
  5. pH is within the stated range.
  6. Media has the proper appearance and consistency (i.e. color, clarity, gel strength of agar, etc.).
  7. Media container must have the proper fill amount.
  8. Packaging and labeling information was reviewed for accuracy.

ATCC is a registered trademark of the American Type Culture Collection.
Tween is a registered trademark of ICI Americas, Inc.


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