Unknown bacteria flow chart gram negative

Here is the eight steps identification of gram negative bacteria in microbiology.

1. Start: Unknown Bacteria
   • Perform a Gram Stain to confirm the bacteria is Gram-negative (pink cells).

2. Step 1: Cell Morphology and Arrangement
   • Observe under a microscope:
     • Bacilli (Rod-shaped): Continue to Step 2.
     • Cocci (Spherical): Test for oxidase activity to differentiate Neisseria and Moraxella (oxidase-positive) from other cocci.

3. Step 2: Oxidase Test
   • Oxidase-positive: Likely Pseudomonadaceae or Vibrionaceae.
     • Perform extra tests like motility and glucose fermentation.
   • Oxidase-negative: Enterobacteriaceae family; proceed to Step 3.

4. Step 3: Lactose Fermentation (MacConkey Agar or TSI Test)
   • Lactose fermenters (pink on MacConkey agar): Possible genera:
     • Escherichia coli: Confirm with indole and methyl red (positive).
     • Klebsiella: Non-motile, urease-positive.
     • Enterobacter: Motile, ornithine decarboxylase-positive.
   • Non-lactose fermenters (no color change on MacConkey):
     • Proceed to Step 4.

5. Step 4: H2S Production (TSI Slant or SIM Test)
   • H2S-positive: Likely Proteus, Salmonella, or Edwardsiella:
     • Proteus: Swarming motility, urease-positive.
     • Salmonella: Lysine decarboxylase-positive, citrate-positive.
     • Edwardsiella: Indole-positive, found in aquatic environments.
   • H2S-negative: Proceed to Step 5.

6. Step 5: Urease Test
   • Urease-positive: Likely Proteus or Klebsiella.
     • Proteus: Swarming motility, phenylalanine deaminase-positive.
   • Urease-negative: Proceed to citrate utilization test.

7. Step 6: Citrate Utilization Test
   • Citrate-positive: Citrobacter, Salmonella.
   • Citrate-negative: Likely Shigella (non-motile, lactose-negative).

8. Step 7: Motility Test
   • Motile: Differentiates motile genera (e.g., E. coli, Proteus) from non-motile (e.g., Shigella, Klebsiella).

---

Final Identification

Combine the results from all tests, including:

• Gram stain
• Cell morphology
• Oxidase test
• Lactose fermentation
• H2S production
• Urease activity
• Citrate utilization
• Motility test