Slanetz-Bartley Medium ISO

Description

Note: the color tone (light amber / pale pink) can vary between batches without modifying the characteristics of the medium.

Technique

For the membrane filtration technique, take 100 mL of a well mixed water sample, and pass it through a sterile membrane filter. Then, wash with 30 mL of sterile water to rinse the funnel of the filtering system.

Transfer the membrane aseptically to the culture medium contained in a Petri dish, making sure that the filter surface faces upwards. Close the lid and invert the plate. Incubate at 36 °C for 48 hours.

The developed colonies that appear red or purple in colour must be considered as enterococci, since these bacteria reduce triphenyltetrazolium-HCl to an insoluble formazan which is red in colour. The secondary or accompanying Gram-negative bacteria are inhibited by sodium azide.

For food samples, from a decimal dilution bank of the sample, spread 0.1 mL of the dilutions onto the plated medium using a Drigalski loop. Incubation and examination are then carried out in the same way as in the membrane filtration technique.

Note: the presence of enterococci must be confirmed with complementary biochemical tests (catalase, esculin, etc.).

LC-4710, 55 mm plates for filtration purposes

Using sterile forceps, transfer the membrane aseptically to the culture medium contained in a Petri dish, making sure that the filter surface faces upwards. Close the lid and invert the plate. Incubate at 36 ± 2 °C for 44 ± 4 hours.

Physical/chemical control

Microbiological control

Membrane filtration / practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ CFU for selectivity.

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

Aerobiosis. Incubation at 36 ± 2 °C, reading at 44 ± 4 h.

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.

• ATLAS, R.M. and L.C. PARKS (1993) Handbook of Microbiological Media. CRC Press. Boca Raton. Fla. USA.
• ISO 7899-2:2000 Standard. Water Quality. Detection and enumeration of enterococci by membrane filtration method.
• ISO 11133:2014/Amd 1:2018. Microbiology of food, animal feed and water. Preparation, production, storage and performance testing of culture media.
• LACHICA, LV.F. and P.A. HARTMAN (1968) Two improved media for isolating and enumerating enterococci in certain frozen foods. J. appl. Bact. 31:151-156.
• SLANETZ, L.W. and BARTLEY, C.H. (1957) Numbers of enterococci in water, sewage and faeces determined by the membrane filter technique with an improved medium. J. Bact. 74:591-596.
• UNE-EN ISO 11133 (2014). Microbiología de los alimentos para consumo humano, alimentación animal y agua - Preparación, producción, conservación y ensayos de rendimiento de los medios de cultivo.