Question

what are the steps you will take to isolate and identify a salmonella sp.

Answer 1

Ans :-) Salmonella was isolated from cury samples by standard microbiological methods and was confirmed by biochemical tests. The antibiotics susceptibility test was conducted by disc diffusion method using commercially available antibiotics such as ampicillin, tetracycline, chloramphenicol etc.

Sample collection :-

A total of 50 samples were collected from 18 different food stalls. All the samples were collected in bags provided by restaurant not in pre sterilised bag. Then thses samples were brought immediately to laboratory for microbiological analysis.

Isolation of Salmonella :-

Each sample was thoroughly mixed and inoculated on to Salmonella - Shigella agar using sterile swabs and then incubated for 48 hrs. The presumptive Salmonella colonies were then sub cultured by streaking on to the fresh SS agar using a sterile inoculating loop and incubated for 48 hrs at 35°c.

Identification of Salmonella isolates :-

Since the selective media was used for Isolation, the presumptive Salmonella isolates were identified by two confirmatory biochemical tests - triple sugar, iron, agar test and urease test. The presumptive Salmonella colonies were directly stabbed into the TSI agar slant. The inoculated samples were incubated with loosened caps for 24 hrs. For urease test 2 loopful of pure and well isolated Salmonella colonies were inoculated into urea broth. The inoculated tubes were shaken gently and incubated with loosened caps for 48 hrs. The TSI agar was checked for the production of hydrogen sulphide gas and the alkalinity while urease test was checked for degradation of urea in urea broth.