This culture medium complies with the recommendations of the International Organization for Standardization (ISO) (1977), the International Dairy Federation (Internationaler Milchwirtschaftsverband, FIL/IDF) (1990) and the DIN Norm 10178 for the examination of milk.
Mode of Action
The growth of staphylococci is promoted by pyruvate, glycine and above all by a high concentration of mannitol. Gramnegative contaminants are inhibited by lithium chloride (LAMBIN and GERMAN 1961) while Gram-positive contaminants are inhibited by tellurite. Micrococci are suppressed to a certain degree because of anaerobiosis. Growth of staphylococci can be recognized by a black colouration of the culture medium due to reduction of tellurite to metallic tellurium.
Typical Composition (g/litre)
Peptone from casein 10.0; meat extract 5.0; yeast extract 5.0; lithium chloride 5.0; D(-)mannitol 20.0; sodium chloride 5.0; glycine 1.2; sodium pyruvate 3.0; Tween® 80 1.0.
Also to be added: potassium tellurite trihydrate 0.052 g/litre.
Suspend 55 g/litre. In accordance with the ISO recommendations, dispense 19 ml aliquots into test tubes, autoclave (20 min at 121 °C), cool, add 0.1 ml of a 1 % potassium tellurite solution to each tube. pH: 6.9 ± 0.2 at 25 °C.
The prepared broth is clear and yellowish-brown.
The prepared culture medium base can be stored for about 2 weeks in the refrigerator. The ready-to-use medium must be used the day it is prepared.
Experimental Procedure and Evaluation
Homogenize the sample material and prepare dilution series (dilution factor 1 in 10). Inoculate each tube containing the broth with a 1 ml aliquot, overlay with sterilized paraffin viscous.
Incubation: 18-24 hours at 35 °C aerobically.
Streak material from tubes that exhibit a black colouration onto selective culture media (e.g. BAIRD-PARKER Agar). When determining the bacterial count by the MPN method, tubes are considered positive for Staphylococcus, if they produce a positive result in the coagulase test