IDENTIFICATION OF BACTERIA

Question 1

Steps in isolation & identification

Answer 1

Step 1. Cultural Characteristics – Streaking culture plates
• Incubate plates (e.g. 24 hr)
• Colonies appear on plates
• Note size, texture, color, hemolysis • Growth requirements (O2, temp, pH)

• Step 2. Morphological & Staining Xtics – Colonies Gram stained
  – Cells observed microscopically
  – Gram stain morphology
  • Shape
  – cocci (round)
  – bacilli (rods)
  – spiral or curved (e.g. spirochetes) • Single or multiple cells
  – clusters (e.g. staphylococci) – chains (e.g. streptococci)
  – Gram +ve or Gram -ve
• Step 3. Biochemical Characteristics
  – Isolated bacteria are speciated generally using biochemical tests
  • Based on the presence of various enzymes
  • Ferment sugars (glucose and lactose)
  • Produce an acid which may be detectable by a colour change of an indicator present in the medium
  • produce gas which may be detected as a bubble in the medium
  • Etc.
• Step4.Antibioticsusceptibilitytesting