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Culture Media Preparation

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Culture Media Preparation

Culture Media Preparation


Culture Media Preparation Workflow – Summary of a Typical SOP


Type of productTestPurpose
Non-sterileMicrobial enumeration testsCounts the total number of bacteria and/or fungus in a product sample
Non-sterileTests for specific organismsIdentifies objectionable organisms, such as Salmonella, in a product sample
SterileSterility testsChecks sterility of a product sample


European Pharmacopoeia (EP)US Pharmacopoeia (USP)Japanese Pharmacopoeia (JP)
2.6.12: Microbial Examination of Non-sterile Products: Microbial Enumeration Tests<61>: Microbial Examination of Non-sterile Products: Microbial Enumeration Tests4.05 I: Microbial Examination of Non-sterile Products: Microbial Enumeration Tests
2.6.13: Microbial Examination of Non-sterile Products: Tests for Specified Microorganisms<62>: Microbial Examination of Non-sterile Products: Tests for Specified Microorganisms4.05 II: Microbial Examination of Non-sterile Products: Tests for Specified Microorganisms
5.1.4: Microbiological Quality of Non-sterile Pharmaceutical preparations and substances for pharmaceutical use<1111>: Microbiological Examination of Non-sterile Products: Acceptance criteria for pharmaceutical preparations and substances for pharmaceutical use12: Microbiological Examination of Non-sterile Products: Acceptance criteria for pharmaceutical preparations and substances for pharmaceutical use 


European Pharmacopoeia (EP)US Pharmacopoeia (USP)Japanese Pharmacopoeia (JP)
2.6.1: Sterility<71>: Sterility Tests4.06: Sterility Test


Culture Media expert


Challenges of Culture Media Preparation


Culture Media Featured Solution from METTLER TOLEDO


Culture Media Formulation Methods


Workflow Optimization and Comprehensive Data Management


Measuring the pH of Your Culture Media


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1. What is the easiest way to recalculate the recipe quantities when the target amount is not 1 liter?

To avoid the risk of errors, the best way to recalculate errors is electronically. If the recipe quantities are available in a spreadsheet, the new values can be calculated quickly. When using an XPR precision balance, you can set up your culture media formulation method to prompt you to enter the required volume and the target amounts will be calculated automatically. The balance will prompt you for the required amounts.


2. How can I ensure that the ingredient weights are within tolerance?

The weighing tolerances should be defined in your culture media preparation SOP. They may be specified precisely or given as a percentage. If you need to change the recipe volume, there is the additional challenge of also recalculating the upper and lower weight limits related to the tolerances. With XPR precision balances, the tolerances are included as a percentage when the culture media recipe is created. The upper and lower weight limits are calculated automatically for any target volume. The built-in weighing in guide helps you to dose to target, displaying green if you are within the tolerance range.


3. My culture media recipe is printed out as a list of ingredients. What is the best way to keep track of where I am in the process?

The simplest way is to organize your culture media ingredients according to the list and tick them off one by one as you add them. However, this process must be carried out diligently to avoid mistakes. By saving your culture media SOP as a method on your XPR balance, the balance will prompt you for each ingredient by name and with the required quantity. Once you have weighed the ingredient, the weight result and the ingredient name is saved automatically to the built-in results protocol which you can view at any time. The balance tares automatically and prompts you for the next ingredient.


4. In our microbiology lab, we write down the actual weights of the ingredients by hand. How can we avoid mistakes and speed up the process?

On our XPR balances, the weights of the culture media ingredients are saved automatically to the built-in results protocol and can be viewed at any time. The final results can be printed out or transferred to a PC.


5. What is the best balance for culture media preparation?

The best balance depends on your application and your accuracy requirements. When choosing your balance you need to consider:

  • The smallest amount you want to weigh
  • The maximum load that will be placed on the balance
  • The level of accuracy you require
  • The criticality of the application

In metrology terms, these considerations are necessary to define the minimum weight requirement, the capacity of the balance and the safe weighing range. METTLER TOLEDO's free GWP® Recommendation service helps you choose the right balance for your needs and determines if your existing balance is fit for purpose.


6. How can we ensure compliance with regulations?

XPR balances incorporate quality assurance functions so you can be sure that the balance is level and routine tests are up to date before you begin to weigh. The balance status is indicated by the StatusLight™ built into the front of the balance terminal. At a glance, you can see that green means it is safe to weigh, yellow is a warning and errors are shown in red.

The built-in routine test library contains customizable templates for eccentricity, repeatability and sensitivity tests. A record of all routine tests is maintained to provide traceability.

LabX laboratory software provides maximum support for compliance. By implementing your SOPs in LabX, you can be sure that all users follow the same culture media preparation procedures. The software can also manage all quality assurance functions, including the scheduling of routine tests and blocking the balance from use if necessary. All results and process information are saved securely in a central database to ensure traceability and assist with FDA CFR part 11 compliance.


7. When preparing culture media, we sometimes have problems with our balances not settling and reproducibility is poor. What can we do?

When a balance fails to settle, there is a high chance that the weighing cell is being influenced by electrostatic charges or air-drafts.

Electrostatic charges can build up on containers and samples through normal handling so you aren’t doing anything wrong. Sometimes the balance is able to settle but the weight value displayed on the balance may not be the true amount of the substance added, which could explain why reproducibility is poor. To remove electrostatic charges from your containers and samples, free-standing ionizers can be placed next to your balance.

Settling issues can also arise from the use of a safety cabinet or fume hood.

In such environments, turbulent or laminar flow air-drafts can apply a force on the weighing cell preventing the balance from settling and affecting repeatability.

The SmartPan weighing pan on XPR precision balances minimizes the effects of air drafts on the weighing cell. SmartPan provides higher stability than a standard weighing pan enabling results to be delivered up to twice as fast and improving repeatability.


8. How can we ensure our culture media are correctly labelled with all necessary information?

XPR balances incorporate functions to configure sample labels with all the information you require, including automatic calculation of the expiry date. Even barcodes can be added. The label can be printed automatically at the end of the culture media preparation procedure. METTLER TOLEDO labels withstand the temperatures of autoclave sterilization processes.


9. Some of the culture media ingredients have similar colors. How can I be sure I don't add the same one twice?

A good idea is to include barcode labels on your ingredients to uniquely identify each sample. XPR balances support barcode readers; the ingredient barcode is scanned prior to adding it to the culture media mixture so it's easy to check that you have the right ingredient. By connecting your XPR balance to LabX, a warning will be given if you scan the same barcode again so it's not possible to add the same ingredient twice.


10. We have a database of culture media ingredients in our LIMS. How can I transfer the information I need to the balance?

LabX laboratory software is easily integrated with your LIMS to enable bi-directional transfer of information between your LIMS and the instruments connected to LabX, including any balance used for culture media preparation.