Merck Millipore's agar established as basis for ISO Standard

E.coli on CCA media

A culture medium from Merck Millipore has become the only product validated by the International Organization for Standardization (ISO) for enumeration of E. coli and coliforms in water samples with low background flora.

Chromocult Coliform Agar (CCA) has been used by ISO as the only suitable culture medium to develop a revised standard to replace Lactose TTC agar.

The revised ISO 9308-1 standard came into effect on September 16. When countries implement it as national regulation, firms must change from Lactose TTC agar to the chromogenic medium.

Importance of pathogen detection in water

Merck Millipore said detection of potential pathogens in water is a critical function to manage quality control microbiological workflow.

Dr Andreas Bubert, senior product manager culture media food and beverage at Merck Millipore / BioMonitoring, told that the detection of pathogens is also essential for reducing risk of contamination and ensuring consumer safety.

Before a new culture medium can be proposed for inclusion into a new standard, it must be used and experienced across different geographies,” he said.

“Once this period of collecting experience was complete, Chromocult media was proposed by the ISO experts because it fulfilled several important criteria (e.g. time to result, differentiation of E. coli from other coliforms, chromogenic reactions etc). 

“Then, the development of a new ISO standard including extensive validations typically takes three to five years.”

Why CCA?

CCA is available as a dehydrated culture medium and ready-to-use agar plate and is also approved by the US Environmental Protection Agency for the same job.

CCA is based on enzymatic reactions that color the colonies of the target organisms. CCA's detection of coliform bacteria and E. coliprovides earlier results, easier lab procedures and colony identification improves the testing of samples with low background flora.

It enables subsequent identification of growth colonies in case of questionable results and does not require additional culture media for result confirmation.

The ISO standard was developed for drinking water samples for human consumption which typically have a low bioburden.

The chromogenic medium is not designed for enumeration of E. coli or coliforms in waste water or raw untreated water.

It enables the simultaneous detection, differentiation and enumeration of E.coli and coliform bacteria in water within 24 hours, which speeds time-to-result by a day compared to Lactose TTC agar, claims the firm.

Alternative methods exist, which also provide results in 24 hours, but are more expensive than CCA.

Merck Millipore's EZ-Pak membrane filters and Bactident Oxidase strips, which are used to confirm coliform bacteria, were included in the validation process.

The combination of the filter and strips, with the CCA media provide a validated approach for detecting and enumerating E.coli and coliform bacteria in water samples.

The method will enable food and beverage laboratories to reduce their validation processes, provide quicker time-to-results and allow products to reach market sooner, said the firm. 

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