It is essential that all microbiological tests are quality controlled to guarantee the result is true and this will normally form part of a laboratory's accreditation compliance. Part of the QC procedure requires that standard or type culture organisms are used to represent 'real samples' but in a controlled manner. These should be traceable back to a known type culture with normally less than five subcultures or passes (repeated subculture of organisms can result in possible genetics changes or contamination). Many organisms for QC are available commercially in a range of different presentations, these are easy to store, easy to use (with little or no preparation time), economical and most importantly reliable and consistent.

There are a range of applications for which these quality control organisms can be used:

• Media QC
  media prepared in house will require various growth promotion tests according to GLP, even with commercial ready to use media where most of the QC testing work has already been done, some limited growth promotion testing is still needed, particularly with media containing light or heat sensitive components.
  
  
• Positive and Negative Controls for biochemical tests, kits and slide stains
  using qualitative inoculant for assays, kits and slide staining, the controls should reflect the organism(s) being tested for and demonstrates that the test was correctly performed. Slides for Gram and Acid Fast staining are available with positve and negative control organisms already incorporated.
  
  
• Antimicrobial Efficacy Testing or MIC Determination
  reference strains of bacteria with known sensitivites are tested in parallel with the clinical culture to to monitor antimicrobial content of the discs/broths and the performance of the media and incubation conditions.
  
  
• Determining Measurement of Uncertainty (MOU)
  as no method is perfect, by using a quantitative inoculum the amount of uncertainty for a particular assay can be calculated, commercial products are an easy standardised way of using a known inoculum number.
  
  
• Determining Limits of Detection
  of qualitative or quantitative routine testing or for method validation, particularly useful if naturally contaminated materials rarely occur.
  
  
• Challenge testing /Preservative Efficacy Testing (PET)
  using quantitative preparations of known organisms a products preservative system can be challenged and monitored using a reliable and consistent inoculum.
  

Packaged QC organisms are also very useful during method validation, particularly for determining measurement of uncertainty (MOU), limits of detection and other tests where a quantitative inoculant is required. When using the quantitative systems they provide greater precision and consistency batch-to-batch than self prepared organisms.

The format the QC organisms are supplied in varies, from a film of preserved organisms in the lid of a vial to freeze-dried discs or beads. All are rehydrated in some form prior to use. Some need to be kept refrigerated, others require freezing. The systems supplied in vials can be used with a pipette or culture loop, others are presented in a swab format that can be streaked directly onto a plate.

ATCC Licensed Derivative Program
The American Type Culture Collection, ATCC, runs a license program to ensure the integrity of culture organisms purchased in commercial formats. The ATCC Licensed Derivative emblem assures customers of the quality of the ATCC ingredient contained in the product. Companies who are members of this scheme are denoted with an asterisk in the tables below.

Most freeze dried/lyphilized products now come with an easy re-hydration step using supplied fluid, followed by inoculation by swab or loop.