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Salmonella, a genus of rod-shaped gram-negative bacteria within the Enterobacteriaceae family, is responsible for the second most common intestinal infection, known as "Salmonellosis." Salmonella outbreaks are frequently linked to contaminated eggs, meat, poultry, fruits, and vegetables. The two most common Salmonella serotypes are typhimurium and enterica, causing non-typhoidal and typhoidal diseases, respectively. Symptoms of Salmonella infection include diarrhea, abdominal cramps, and fever, with potential complications like focal infection and reactive arthritis. In most cases, Salmonella infections last for 3-7 days, with an infectious dose ranging from 10^3 to 10^9 bacterial cells per gram of food.
During this experiment, a group of three students, under the guidance of our lab instructor, conducted the following steps:
This dilution was then added to Selenite cysteine broth and incubated for 24 hours at 35°C, as Salmonella can thrive in this medium due to the presence of sulfur in cysteine.
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These plates were incubated for 24-48 hours at 35°C.
| Media | Characteristics |
|---|---|
| Bismuth Sulfate (BS) | Black shiny metallic sheen-like colonies |
| Brilliant Green Sulfa (BGS) | Fade pink-like colonies |
| Mackoney (MAC) | Transparent/colorless colonies |
Observations of colonies on the cultured selective media were as follows:
Mackoney agar is a non-lactose fermenter.
The selected colonies were marked on the plates and isolated for biochemical testing. Isolated colonies from three plates were taken, added to a sterile solution, and mixed thoroughly. The sample was then pipetted into three Triple Sugar Iron (TSI) test tubes corresponding to MAC, BS, and BGS, respectively. A sterilized loop was used to inoculate the test tubes, and they were incubated for 24 hours at 35°C.
For API 20E testing, the sample from the prepared solution was added to each well of the API sheet and incubated for 24 hours at 35°C. Reagents were added to specific wells post-incubation, and reactions were observed and recorded using the API interpretation table.
| Wells | Reactions |
|---|---|
| GEL | Fill completely with the sample before incubation |
| CIT | Fill completely with the sample before incubation |
| VP | Fill completely with the sample before incubation; additional reagents added (1 drop of iodine reagent in IND well, 1 drop of VP A and 1 drop of VP B in VP well, 1 drop of ferric chloride in TDA well) |
| GLU | 1 drop of oil is added |
Based on the testing, the results were as follows:
| Media | Results |
|---|---|
| BS | Unacceptable identification/profile |
| BGS | Excellent identification of Proteus mirabilis |
| MAC | Excellent identification of Proteus mirabilis |
Unacceptable profiles can result from impurities or mixed purities on the cultured plates, which can be influenced by physical, chemical, or external factors. In the case of BS, an unacceptable profile was observed. However, excellent identification of Proteus mirabilis was achieved for BGS and MAC. No Salmonella was detected in any of the three samples, indicating that the tested food sample does not contain any Salmonella species.
Lab Report: Isolation and Identification of Salmonella. (2024, Jan 06). Retrieved from https://studymoose.com/document/lab-report-isolation-and-identification-of-salmonella
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