Scientists investigated the effectiveness of five different antibiotics on the Salmonella bacteria in the outbreak. Antibiotics A, B, C, D and E were used in the investigation. Figure 4 shows the results. Describe two aseptic techniques the scientists should have used in the investigation.

Aseptic techniques are vital to ensure that the results of a microbiology investigation are valid and not due to contamination. Key techniques include: 1. **Sterilisation of equipment:** All equipment, including the Petri dish, nutrient agar, and inoculating loop, must be sterilised before use to kill any existing microorganisms. This is often done using an autoclave (high-pressure steam) or, for a metal loop, by passing it through a hot Bunsen flame until it glows red. 2. **Sterilisation of work area:** The work surface should be wiped down with disinfectant. 3. **Preventing airborne contamination:** Working near a lit Bunsen burner creates a convection current (an updraft of hot air) which carries airborne microbes away from the open Petri dish. The lid of the dish should also be lifted as little as possible. 4. **Securing the culture:** After inoculation, the lid of the Petri dish should be secured with pieces of tape to prevent it from falling off, but not sealed all the way around, to prevent the growth of harmful anaerobic bacteria.