Question

Make flowcharts to show the traditional biochemical tests used in a microbiology lab to identify the following organisms. Start from gram stain used to identify gram negative bacteria.

1. E.coli
2. salmonella spp.
3. yersinia spp.
4. Shigella
5. Klebsiella
6. Citrobacter
7. serratia
8. Providencia
9. proteus
10. pseudomonas aeruginosa
11. acinetobacter
12. alcaligenes
13. chryseobacterium

Answer 1

Gram staining also called grams method

It a staining method that is used to distinguish the bacteria two large groups that are

Gram positive and

Gram negative.

Gram positive bacteria - They have thick layer of peptidoglycon in the cell wall that retains the primary stain that is crystal violet.Lugols iodine solution is always added after addition of crystal voilet to strengthen the bonds of the stain with cell membrane.

Gram negative Bacteria have thinner peptidoglycon layer that causes the crystal voilet to wash away on addition of ethanol.

The traditionally biochemical tests to used to identify these gram negative bacteria are IMVIC reactions.

1)E.coli

Gram negative bacteria

Lactose positive on MacConkey agar.

Indole test - Positive (red ring)

Methyl red test- Positive(Bright red)

VP test- negative( no change colourless)

Citrate test - negative (no change green colour)

2) Salmonella

Gram negative bacteria

Non lactose fermenting organisms

Indole test- negative

Methyal red test -positive.

VP test- Negative

Citrate test-postive

3)Yersinia - gram negative

Indole test- negative

Methyl red test - positive

VP test- negative

Citrate -negative

Catalse- positive

Oxidase- negative

Urease -negative

4)Shigella -gram negative bacteria

Non lactose fermenting bacteria

Indole test - negative

Methyl red - positive or negative

VP test - Positive

Citrate - Negative.