SIST EN ISO 6222:1999

SIST EN ISO 6222:1999 is the Slovenian standard published by SIST for water microbiology. It specifies a culture-based method for enumerating culturable micro-organisms in water by colony count on nutrient agar after aerobic incubation at 36 °C and 22 °C. It is intended for people who test water quality, especially public drinking water, water for human consumption, water in closed containers, and natural mineral waters.

What does SIST EN ISO 6222:1999 specify?

SIST EN ISO 6222:1999 specifies a colony-count method for culturable micro-organisms in water and sets out how to sample, culture, count and report the results. The document is organized into scope, normative references, one definition, principle, apparatus and glassware, sampling, culture media and diluents, procedure, expression of results, and test report.

The scope makes clear that the method is used to assess the operational efficiency of drinking water treatment and for general water microbiology. In practice, this means the test is suitable both for routine plant control and for broader checks of water quality.

What are the key requirements of SIST EN ISO 6222:1999?

Clause 4 - how the count is obtained

SIST EN ISO 6222:1999 uses inoculation of measured sample volumes or dilutions into Petri dishes with a specified nutrient agar medium, followed by aerobic incubation at two temperatures. One set of plates is incubated at 36 °C and another at 22 °C, and the result is calculated as colony-forming units (cfu) per millilitre. In practice, this gives two complementary counts that help show how the water behaves under different growth conditions.

Clause 6 - sampling and sample handling

SIST EN ISO 6222:1999 requires sampling in line with the referenced sampling and preservation standards. Water supplied in closed containers, including natural mineral waters, is to be examined within 12 hours of bottling and kept at 5 °C to 3 °C during that period. This matters because delay or poor storage can change the colony count before the test starts.

Clause 7 - medium and diluent preparation

SIST EN ISO 6222:1999 specifies yeast extract agar for the count and a peptone diluent for dilutions. It also requires water suitable for analytical laboratory use and allows either ingredients of uniform analytical grade or an equivalent dehydrated complete medium used according to the manufacturer’s instructions. For the laboratory, this means the medium and diluent must be prepared consistently so the result reflects the water sample, not the reagents.

Clause 8 - plate preparation, incubation and counting

SIST EN ISO 6222:1999 uses the pour-plate method, with the sample and molten medium mixed in the dish before the agar sets. The time between adding the sample and adding the molten medium is limited, and at least one plate is prepared for each incubation temperature. Plates are inverted, incubated, examined promptly, and rejected if growth is confluent; counts are then made using the procedures in ISO 8199. This keeps the count readable and comparable between tests.

Clauses 9 and 10 - reporting

SIST EN ISO 6222:1999 requires results to be expressed as cfu/ml for each incubation temperature. It also gives the reporting approach when no colonies are found in the undiluted sample or when the plates are too crowded to count reliably. The test report must identify the sample, the pour-plate technique and medium, the incubation conditions, the results, and any relevant observations during the analysis.

What terms does SIST EN ISO 6222:1999 define?

• culturable micro-organisms - aerobic bacteria, yeasts and moulds that can form colonies under the test conditions.
• colony-forming units (cfu) - the unit used to express the estimated number of colonies per millilitre of sample.
• pour-plate method - a technique where sample and molten medium are mixed in a Petri dish before incubation.
• confluent growth - growth so heavy that individual colonies cannot be counted reliably.
• yeast extract agar - the specified nutrient agar medium used for the colony count.
• operational efficiency of the treatment process - the use of colony counts to check how well public drinking water treatment is working in practice.

Who uses SIST EN ISO 6222:1999?

SIST EN ISO 6222:1999 is used by water testing laboratories, microbiologists, and quality staff in public drinking water supply systems. It is also relevant to operators and laboratories working with water intended for human consumption, water in closed containers, and natural mineral waters. These users apply it for routine monitoring, treatment control, and investigation of unexpected changes in colony counts.

What changed in SIST EN ISO 6222:1999 from the previous edition?

SIST EN ISO 6222:1999 supersedes SIST ISO 6222:1997. The standard is the second edition of ISO 6222 and cancels and replaces ISO 6222:1988, which it says was technically revised.

Which standards are used with SIST EN ISO 6222:1999?

• EN ISO 3696 - provides the water quality used to prepare media.
• EN ISO 5667-3 - gives guidance on preservation and handling of samples.
• EN 25667-2 - gives guidance on sampling techniques.
• ISO 6887 - provides general guidance for preparing dilutions for microbiological examinations.
• ISO 8199 - gives the general guide for enumerating micro-organisms by culture and supports dilution preparation, the pour-plate approach, and colony counting.

What does the SIST EN ISO 6222:1999 document contain?

The document contains the full test workflow from sampling to reporting. It includes the apparatus list, the required incubation equipment, and the specified Petri dish sizes and counting setup. It also gives the yeast extract agar formulation and preparation instructions, the sample and dilution handling steps, and the rules for reading plates and expressing results. For laboratories, it is a practical method document for routine water microbiology testing and reporting.