Salmonella count

Alex Castillo castillo at tamu.edu
Fri Aug 14 21:27:02 EST 1998


You can do an MPN count for Salmonella. Several papers have been published
on MPN for Salmonella.

DES O'CONNOR wrote in message <01bdc781$0e273100$LocalHost at default>...
>Dear Roberta,
>
>                     I hope the following information helps. Salmonella can
>be quite difficult to enumerate due to poor recovery on solid media without
>any pre-enrichment or resuscitation stage. Some years ago a group at
>Barcelona or perhapes, Madrid University published papers reviewing
>comparative methods of recovering Salmonella on solid media; you could
>trace that down.
>
>My suggestions are :-
>
>1) Surface plating (37' c 2 days) on Tryptone soya or Columbia agar. Follow
>this with replica platting of the incuated plates onto X.L.D. and or
>Bismuth Sulphite agar. This approach permits non selective resusciatation
>followed by replication of colonies on differential media. You will of
>course still have to conducted confirmatroy serology and biochemistry.
>I've tried this and I consider it is a good approach.
>
>2) A less accurate system could be developed along the lines of the MPN
>technique commonly used for enumeartion of of Coliforms in water. It might
>be possible to develop a system based on a suitabley selective self
>indicating broth. I believe there is such a system called L.I.N.C.R. which
>was developed some years ago and may be still avialable through Oxoid or
>Difco.
>
>The latter ( I think) is basically a Lysiene decarboxylase broth containing
>a sensitive H2S indicator. At 42'c premuptively positive dilutions of food
>turn black. Such tubes may be subbed to selective media for serological and
>biochemical confirmation. MPN table may then be used to produce a most
>probabale level of contamination.
>
>Best
>
>Des O'c





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