Question

Create DICHOTOMOUS KEY showing which selective media and biochemical tests you would need if you were to test your unknown bacteria (SALMONELLA ENTERICA) in the lab and also, describe the dichotomous key of Salmonella Enterica in paragraph like in example shown below.

[[ Like this is example for Staphylococcus epidermis shown by my professor: You would say this. According to my unknown bacterium 16S DNA sequence result from NCBI database, my unknown bacterium was identified to be Staphylococcus epidermidis. To identify and confirm Staphylococcus epidermidis bacterium in lab traditionally using culture and media, I would first grow the bacterium in nutrient broth, then using the grown culture, I would perform Gram Staining, which should show me purple cells under microscope because this bacterium is gram-positive, then I will procced to testing for Catalase enzyme. This test would help me differentiate Staphylococcus from Streptococcus. The catalase test should be positive. Then, I will test for coagulase enzyme to make sure it is negative because coagulase positive would indicate my bacterium is Staph aureus. Then, I would test for oxidase enzyme to make sure it is negative. Positive oxidase enzyme would indicate my bacterium is Micrococcus. Then, I would perform Kirby-Baur assay using novobiocin antibiotic to test for the antibiotic sensitivity. The larger zone of inhibition means the bacterium is sensitive to novobiocin, which indicates the the bacterium is Staphylococcus epidermidis.

The selective media we can use to ID Staphylococcus Epidermis is the MSA (Mannitol Salt Agar).]]

Like wise in the same way, as above example for Staphylococcus Epidermis, 1) Create DICHOTOMOUS KEY showing which selective media and biochemical tests you would need if you were to test your unknown bacteria (SALMONELLA ENTERICA) in the lab and 2)Describe the dichotomous key of Salmonella Enterica in paragraph like in example shown.

Answer 1

Solution

Identification and confirmation of Salmonella enterica

1. Bacterial Culture

The bacteria was grown on nutrient agar media. Smooth white round glossy colonies were obtained.

2. Gram staining

Bacteria from one of the colonies from the nutrient agar plate was subjected to Gram staining. Pink colored (safranin stained) rod shaped cells were observed under the light microscope. This indicates that the bacteria is Gram-negative bacilli.

3. Biochemical tests to identify the Gram-negative bacilli

(a) Test for glucose fermentation

The result differentiates between glucose fermenters and non-fermentors.

Result: Positive result indicates glucose fermentors.

(b) Oxidase test

Oxidase test results differentiate between Enterobacteriaceae family from other glucose fermenting bacteria.

Result: Negative, indicates Enterobacteriaceae family.

Enterobacteriacea family commonly consists of Shigella, Salmonella, Yersinia, Morganella, Serratia, Edwardsiella, Proteus, Providencia.

(c) Methyl red test (MR)

This test differentiates between Serratia from the rest in the group Enterobacteriaceae.

Result: MR positive, rules out Serratia.

(d) Motility test

This test rules out Shigella.

Result: Positive, indicates the bacteris is not Shigella.

(e) Phenyalanine deaminase

This test differentiates between Proteus, Providentia, Morganella versus Salmonella, Yersinia, Edwardsiella.

Result: Negative, indicates either of Salmonella, Yersinia or Edwardsiella.

(f) H2S test

This test eliminates Yersinia from Salmonella, Yersinia or Edwardsiella.

Result: Positive, indicates the bacteria is either Salmonella or Edwardsiella

(g) Indole test

This test differentiates between Edwardsiella and Samonella.

Result: Negative indicates the bacteria is Salmonella sp.

Salmonella sp. can be divided into Salmonella bongori and Salmonella enterica.

To differentiate between the two we need to perform molecular serotyping using genomic isolation, PCR amplification with suitable primers, sequencing and database mining (alignment tools).

The selective media that is used for Salmonella sp. : Xylose-Lysine-Deoxycholate agar produces black colonies (due to H2S) indicates Salmolella.

The Dichotomous Key