Rapid Detection of Coliforms in Yogurt

What are coliforms?

Coliforms are a group of bacteria commonly found in the environment, including soil, surface water, vegetation and the intestinal tracts of warm-blooded animals. Most coliforms do not cause disease, but a small percentage can cause illness in people, especially young children, the elderly, and those with weakened immune systems. Coliforms are rod-shaped Gram-negative non-spore forming organisms. They can ferment lactose with the production of acid and gas when incubated at 35-37°C. Coliform bacteria are not a traditional taxonomic group, like Salmonella, Escherichia coli, or Listeria. Instead, the coliform bacteria are a collection of strains in the Enterobacteriaceae family. E. coli, Enterobacter spp., Klebsiella spp., and Citrobacter spp. are the most common coliforms.

How do coliforms get into milk?

Coliform bacteria are normally shed in the feces of healthy livestock, including dairy cattle. Thus, poor herd hygiene, contaminated water, unsanitary milking practices, and improperly washed and maintained equipment can all lead to elevated coliform counts in raw milk at the dairy farm. The milking of cows with wet and manure-soiled udders and inadequately cleaned milking equipment are the most common ways for coliform bacteria to enter milk on-farm.

Coliforms in milk: What does it mean?

The coliform bacteria count is used as an index of the level if sanitation and/or water quality employed in the handling and processing of milk products. In dairy products, the process of pasteurization easily kills coliform bacteria. Therefore, the finding of coliforms in pasteurized products indicates some level of contamination has occurred after pasteurization during product manufacturing or packaging. Hence, coliforms are used as a general indicator of sanitary conditions in dairy production and processing environments.

Traditional methods for testing Coliforms

Traditionally the agar plate count method using VRBA (Violet Red Bile Agar) and the MPN methods are being used.  The plate count method takes 24 hours to perform and can use 1.0 ml of 1:10 dilution and as a result has a sensitivity of <10 cfu/gram.

When higher sensitivity is required the MPN (Most Probable Number) method can be used.  Multiple tubes (typically 3) are inoculated for each dilution.  The method involves the inoculation of at least 3 decimal dilutions (a total of 9 tubes) of LST (Lauryl Tyrptose Broth).  Any LST tube that shows growth and gas production is transferred to BGLB (Brilliant green lactose bile), the MPN is calculated based upon the positive BGLB tubes.  This assay is very labor intensive and takes 3-5 days to complete.

Rapid High volume Automated Method for the Detection of Coliforms

Direct inoculation of Product and Speed to Results

In a recent study 25 different types of yogurts were tested by the BioLumix method and the plate count method.  The BioLumix ready to use vials were directly inoculated with 1.0 ml of various yogurts and monitored in the BioLumix system for 12 hours.  Figure 1 shows the curves obtained.  Key:  Dark blue – Grape yogurt, Green – Grape yogurt inoculated with Citrobacter, Lt Blue – Raspberry yogurt, and Red – Raspberry yogurt inoculated with E. coli.

 All products tested using the automated BioLumix assay for coliforms yielded results in a considerably shorter test time (typically 10-12 h) than the conventional Violet Red Bile Agar (VRBA) method (24 h to 72 h with confirmation). The BioLumix method can detect <1 cfu/gram of product, being 10 times more sensitive that the plate count method.  The BioLumix coliform medium had better selectivity in detecting coliforms, eliminating the need for the confirmation step.

Labor Savings

The BioLumix System offers a significant reduction in time to obtain results while reducing hands-on labor due to its automation and simplicity of use.  The procedure involves 2 simple steps:

  1. Add 1.0 ml of product directly to the ready to use vial
  2. Add the sample information to the computer

The system automatically will run the system and generate the desired reports. Therefore, there is no sample preparation required no media preparation or counting of plates.  Due to its simplicity the assays can be performed by less skilled personnel.


The BioLumix system is a fully automated system offering automated data achieving, and automated reporting.  It offers the ability to operate the laboratory as a paperless operation. Due to its connectivity through the Intranet it allows for automated transfer of product release information to the warehouse.

Free Product Trial

Interested in a free product trial?  Contact BioLumix today!  P.734-984-3100.

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