Describe the principle and procedure of Gram staining, provide examples of Gram-positive and Gram-negative bacteria, and identify differentiating tests.

Describe the principle of Gram staining Gram staining differentiates bacteria based on their cell wall composition. Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet-iodine complex, appearing purple. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane, which allows the complex to be washed out by a decolorizer, causing them to stain pink/red with the counterstain.

State the procedure used during Gram staining

• Step 1: Apply crystal violet stain for 1 minute.
• Step 2: Apply Gram's iodine (mordant) for 1 minute.
• Step 3: Decolorize with alcohol or acetone for 10-20 seconds.
• Step 4: Counterstain with safranin for 1 minute.
• Step 5: Rinse with water and blot dry.

Give at least 5 examples of Gram-positive and Gram-negative organisms

• Gram-positive organisms:
  • Staphylococcus aureus
  • Streptococcus pyogenes
  • Bacillus anthracis
  • Clostridium tetani
  • Listeria monocytogenes
• Gram-negative organisms:
  • Escherichia coli
  • Salmonella typhi
  • Pseudomonas aeruginosa
  • Neisseria gonorrhoeae
  • Klebsiella pneumoniae

Identity the test that can be used to differentiate Gram-negative from Gram-positive organisms giving observations that are made and give the test that can be used to confirm Staphylococcus aureus from other Staphylococcus species

• Test to differentiate Gram-negative from Gram-positive organisms: Gram staining
  • Observations: Gram-positive bacteria appear purple, while Gram-negative bacteria appear pink/red.
• Test to confirm Staphylococcus aureus from other Staphylococcus species: Coagulase test
  • Observations: Staphylococcus aureus produces coagulase, which clots rabbit plasma, resulting in a clumped or gel-like appearance. Other Staphylococcus species (coagulase-negative staphylococci) do not clot the plasma.

Other than Gram staining, state any other lab test that can be used to make a diagnosis for most of the bacterial infections.

• Bacterial culture and sensitivity testing is widely used. A sample (e.g., blood, urine, tissue) is cultured on agar plates to grow and isolate bacteria. The isolated bacteria are then identified using biochemical tests or molecular methods, and their susceptibility to various antibiotics is determined.