Microbiology

• The aim of the microbiology practical is to investigate the effect of different antiseptics or antibiotics on bacterial growth using agar plates by measuring zones of inhibition.
• The equipment required for the microbiology practical includes an agar plate, a heatproof mat, filter paper discs, three antiseptics such as mouthwash, TCP, and antiseptic cream, disinfectant bench spray, 1% Virkon disinfectant, Antibacterial handwash, forceps, clear tape, hand wash, wax pencil or permanent marker, and an incubator set to 25 o C.
• The method for the microbiology practical involves spraying the bench with disinfectant, wiping it dry with paper towels, marking the bottom of the agar plate with a wax pencil or permanent marker, washing hands with antibacterial handwash, placing the different antiseptics onto different filter paper discs, lifting the lid of the agar plate at an angle carefully and using forceps to place each filter paper disc onto the dots, noting down the antiseptic applied to each zone, taping the lid onto the agar plate securely, but loosely enough that oxygen can still reach the bacteria, and placing t
• The area of the clear zones can be calculated using the formula πr 2.
• The microbiology practical can be repeated with different concentrations of the same antiseptic on the filter paper discs to investigate the optimum concentration of antiseptic used to kill bacteria.
• Safety precautions for the microbiology practical include wearing safety goggles when handling Virkon disinfectant and making sure to wash hands before and after handling the bacteria.
• Sources of error in the microbiology practical include the shape of the clear zone may be irregular and the width is difficult to determine, and contamination from other bacteria may have occurred.