Isolation and identification of Salmonella

By | October 22, 2020

Isolation and identification of Salmonella

Salmonella is gram-negative bacteria, facultatively anaerobic, and facultative intracellular parasite. There are a different kind of test for isolation and identification that are listed below

Biochemical test

In this kind of test, we can identify the salmonella on the basis of ferment so the salmonella in ferment with the maltose, dextrose, mannitol, sorbitol and clearly not fermentate with the lactose and sucrose

By the growth of salmonella

We can grow salmonella on maconky agar, heckton agar, W&B media. it’s basically a media that have a selective and differential media

On selective media

Have gram-negative enterobacter and inhibit the growth of gram-positive bacteria

On diff. media

There are two types of fermentation happen on it lactose and non-lactose fermentation the color occurs respectively bright pink and transparent color colony

By H2S

it can react with triple sugar iron it can produce the h2s gas, and cause a blackish color around the test tube

By agglutination

We can also identify salmonella by agglutination test with salmonella galinaraum take a drop of serum and mix with antigen

Blood cluster

85% of blood cluster are positive

Primary isolation media

  • Blood agar incubate in the air at 35 to 37 c for 18 to 24 hour
  • CLED agar incubate in the air at 35 to 37 c for 18 to 24 hour
  • XLD agar incubate in the air at 35 to 37 c for 18 to 24 hour
  • DCA incubate in the air at 35 to 37 c for 18 to 24 hour

Colony formation

  • on blood agar the colony are moist and 1-2 mm in diameter
  • on CLED it cannot fermentate with lactose but some serotype s.arizonae, s.indiana may fermentate with lactose
  • on XLD red colony appear and a black center
  • on DCA all colonies are black center and colorless colony

biochemical test

ureae test

salmonella can not produce urease

oxidase test

salmonella is oxidase negative if positive appear to discard and take the negative it can agglutinate with the polyvalent o and antiserum then again there are two results positive and negative in negative case urease is added at 37c for an hour then on CLED plate then again watch the negative and positive results discrete positive results now first positive of agglutination and CLDE plate again for biochemical test after that check pure culture there will be two results salmonella related and not related take related and done the agglutination tests




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