Health, disease and the development of medicines study guide

Aseptic techniques are critical procedures used in microbiology laboratories to prevent contamination of microbial cultures, culture media, and the working environment. The primary goal is to minimise the presence of unwanted microorganisms, ensuring that experiments involve only the specific microbes under study and to protect laboratory personnel and the environment from pathogenic organisms. This involves sterilisation of all equipment, growth media, and containers before use. For instance, autoclaves, which use high-pressure steam, are commonly employed to sterilise growth media and Petri dishes. During inoculation, sterile inoculating loops are used to transfer microorganisms, and these loops are often sterilised by flaming immediately before and after use. Maintaining covers on Petri dishes and culture vials, only opening them minimally, and near a Bunsen flame (which creates an upward convection current preventing airborne microbes from settling) further reduces the risk of airborne contamination. These practices collaboratively ensure the integrity and safety of microbiological work.

When investigating how antiseptics, antibiotics, or plant extracts affect microbial cultures, use standard aseptic techniques (disinfecting work areas, wearing gloves and goggles, using sterilised tools) and only permitted, non-pathogenic bacterial species. The independent variable is the type or concentration of antimicrobial agent, and the dependent variable is the zone of inhibition (clear area around the disc) on an agar plate. Control all possible variables, such as the same bacterial strain, agar depth and composition, incubation time, and disc size and placement. Carefully inoculate plates, add antimicrobial discs and a control, seal plates with tape, and label clearly. Incubate plates upside down at or below 25°C for safety. After incubation, do not open the plate – measure the inhibition zone diameter through the closed lid using a ruler. For graphical presentation: display antimicrobial type or concentration on the x-axis and mean zone diameter on the y-axis as a bar graph or line graph. Evaluate the reliability by repeating the experiment, calculating averages, and comparing data; assess uncertainty by comparing the ruler precision (for example, ±1 mm) to the measured zone, then calculate percentage error as (uncertainty/mean) × 100%. Dispose of all cultures and materials by sterilisation (e.g., autoclave) under supervision. Never incubate plates above 25°C or open plates after incubation in schools.