Required Practical: Testing Antibacterial Substances

🧪 Required Practical: Testing Antibacterial Substances

Aim

To investigate the effectiveness of different antibacterial substances against bacterial growth.

Method

1. Prepare agar plates with bacterial culture spread evenly across surface
2. Cut paper discs of equal size (approximately 6mm diameter)
3. Soak discs in different antibacterial substances (antiseptics, antibiotics, natural substances)
4. Include a control disc soaked in distilled water
5. Use sterile forceps to place discs on bacterial culture, spacing evenly
6. Incubate plates at 25°C for 24-48 hours
7. Measure the diameter of clear zones (zones of inhibition) around each disc
8. Calculate the area of zones and compare effectiveness

Results and Analysis

• Clear zones: Areas where bacteria cannot grow due to the antibacterial substance
• Size correlation: Larger zones indicate more effective substances
• Control importance: Water control should show no clear zone
• Quantitative data: Use area calculations (area = pi x r squared) for accurate comparison

Safety and Ethics

• Aseptic technique: Prevent contamination throughout procedure
• Temperature control: Incubate at 25°C, never at body temperature
• Disposal: Autoclave all materials after use
• Hand hygiene: Wash hands thoroughly before and after

Variables

• Independent: Type of antibacterial substance
• Dependent: Diameter/area of zone of inhibition
• Control variables: Temperature, time, disc size, bacterial strain, volume of substance