Dehydration of SMEC Medium and its Application for the Detection of Escherichia coli from Foods

Abstract

In an attempt to explore better selective medium for E. coli from contaminated foods, dehydration of SMEC medium has been studied.
Procedure for preparation of studied SMEC dehydrated culture medium was as follows;
Composition of the medium in 1L was, heart infusion, 4g; casamino acid, 15g; Ltryptophan, 0.05g; lactose, 5g; K₂HPO₄, 4g; KH₂PO₄, 5g: sodium lauryl sulfate, 0.25g; bile salt, 0.5g and 0.2% BCP, 16ml.
Final pH of the medium was 6.2.
Rehydration is made by suspending 33.8g of the above mentioned dehydrated medium in 1000ml of distilled water and boiling until the medium dissolves completely. Then, 10mg of streptomycin was added after cooling down of the solution to 4-5°C.
After being dispensed into fermentation tubes, tubes were subjected to sterilization at 100°C for 60 minutes.
Through application of SMEC dehydrated culture medium to detection of E. coli from various raw meats, following results have been obtained.
1. SMEC dehydrated medium showed the best agreement with MPN of presumptive test and MPN completed test against E. coli.
2. In the SMEC (at 44.5°C) confirmation test against isolated strain from raw meat, positive rate of E. coli group (including type I, II and III) was 88.6% while that of coliform groups was 7.8%.
Above findings were almost identical with the results observed when the original compounded SMEC medium was employed.