ISO 4831 (2006) medium: LST

Media control Food and animal feeding stuffs

Microorganisms and performance criteria for testing selective media 'LST' for Enumeration of Coliforms used in Food and animal feeding stuffs microbiology according to ISO 11133.

  • Qualitative control of Productivity

    • Best Practice LST

    Qualitative single tube method for performance testing of liquid media – pre-enrichment media

    1. Use a reference material or test suspension with a known number of Escherichia coli.
    2. Inoculate the media (LST) with 0.1 mL of more than 100 cfu/mL and less then 1000 cfu/mL of microorganisms.
    3. Incubate at (30 ± 1) °C for (24 ± 2) h to (48 ± 2) h.
    4. Asses the amount of growth as, 0 for no turbidity, 1 for slight turbidity or 2 for good turbidity.
    5. For this medium (LST) and standard (ISO 4831) combination the criteria is: "Turbidity (2) and gas in Durham tube."

    Control strain WDCM number Incubation Criteria Characteristic reaction
    Escherichia coli
    00013 opt
    		 (30 ± 1) °C for (24 ± 2) h to (48 ± 2) h Turbidity (2) and gas in Durham tube Gas production and turbidity
    Citrobacter freundii
    00006 opt
    The best practice for Qualitative control of Productivity for media control of 'LST' is based on the data displayed in this table according ISO 11133.

  • Qualitative control of Selectivity

    • Best Practice LST

    Qualitative control of Selectivity of liquid medium, single culture

    1. Use a quantitative reference material or test suspension with a known number of Enterococcus faecalis.
    2. Inoculate one tube of test medium with >103 cells of non-target organisms.
    3. Incubate at (30 ± 1) °C for (24 ± 2) h to (48 ± 2) h.
    4. Remove 10 µl and streak to a plate of reference medium .
    5. Incubate at (30 ± 1) °C for (24 ± 2) h to (48 ± 2) h.
    6. Growth of non-target microorganisms should comply with the criteria: "No growth".

    Control strain WDCM number Ref. media Incubation Criteria Characteristic reaction
    Enterococcus faecalis
    or
    		(30 ± 1) °C for (24 ± 2) h to (48 ± 2) h No growth No growth
    The best practice for Qualitative control of Selectivity for media control of 'LST' is based on the data displayed in this table according ISO 11133.