Ringer Solution 1/4 ISO

Description

For the routine work with bacteria the solution should be diluted one fourth (Ringer 1/4) and is employed to get cell suspensions or to prepare dilution banks.

Ringer solution does not act as a revitalizer. To dilute food samples or substances that have undergone thermal treatment, it is more advisable to use Peptone Water or Maximum Recovery Diluent (MRD) for the dilutions. They act as a revitalizer.

Due to the low ionic strength of this medium, the pH range of the final value is extended.

Technique

The sample is diluted in a ratio 1:10 with the Ringer and homogenized by a vortex mixer or Stomacher. After a short period (10-15 minutes) of rest, a 1/10 dilution bank with the same diluent is prepared following standard procedures. Plates are inoculated using the range of different concentrations.

Physical/chemical control

Microbiological control

Prepare tubes / inoculate ≤ 10³ CFU/tube (productivity) / subculture after holding at 20-25 °C for 45 min to 1 h.

Microbiological control according to ISO 11133:2014/Amd 1:2018.

Aerobiosis. Incubation at 35 ± 2 °C, reading at 24-48 hours.

Sterility control

Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.

Check at 7 days after incubation in same conditions.

• ISO 6887-1:2017 Microbiology of food chain. Preparation of test samples, initial suspension and decimal dilutions for microbiological examination - Part 1: General rules for the preparation of the initial suspension and decimal dilutions - Part 2 (2003): Specific rules for the preparation of meat and meat products.
• ISO Standard 8199 (2018) Water Quality - General requirements and guidance for microbiological examinations by culture.
• ISO 8261:2001 Standard. Milk and milk products - General guidance for the preparation of test samples, initial suspension and decimal dilution for microbiological examination.
• ISO Standard 10718:2015 Cork stoppers - Characterization of a low-in-germs stopper, through the enumeration of colony-forming units of yeasts, moulds and bacteria, capable of both being extracted and growing in alcoholic medium.
• ISO Standard 11133:2014 Microbiology of food, animal feed and water. Preparation, production, storage, and performance testing of culture media.
• ANONYMOUS (1937) Bacterial Tests for Graded Milk. Memo 139-Foods. Dept. of Health and Social Security. London.
• DAVIS, J.G. (1956) Laboratory Control of Dairy Plant. Dairy Industries Ltd., London.