Published online by Cambridge University Press: 01 June 2009
1. The limitations have been explored of a simplified form of Grimes's litmus milk method, as used for a presumptive test for coliform organisms in butter.
2. To improve on this test, the merits and demerits of renneted litmus milk and litmus milk agar have been investigated, and the latter found preferable.
3. Of 719 samples of export salted butter tested for coliform contamination, only 19·1% gave confirmed positive results using MacConkey broth as the presumptive medium, 21·9% were positive using a litmus milk agar medium, and 30·2% (on 434 samples only) were positive using renneted milk.
4. The coliform organisms isolated were classified into the usual types and a seasonal variation in the coli to aerogenes ratio noted.
5. An observation is made on what appears to be the inhibitory effect of bile salt on the gas production of several strains of the aerogenes-cloacae group isolated in this investigation.
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