Microbiology and pathogens

Describe three aseptic techniques used when culturing bacteria, and why each is used.

A culture was diluted to 10⁻⁵ and 0.1 cm³ of the dilution was spread onto an agar plate. After incubation, 37 colonies grew. Calculate the number of bacteria per cm³ in the original culture.

Figure 2 shows the growth of a bacterial population. Describe and explain the changes between 0 and 28 hours.

Distinguish between bactericidal and bacteriostatic antibiotics, and explain how hospitals can reduce the spread of antibiotic-resistant bacteria.

Describe how Mycobacterium tuberculosis causes disease and how it avoids the immune system.

Explain the role of T killer cells.

For a disease with a basic reproduction number R₀ = 5, the proportion of the population that must be immune for herd immunity is 1 - 1/R₀. Calculate this percentage and explain what it means.

Discuss whether the overuse of antibiotics in farming is a risk to human health.

Plan an investigation to compare the effectiveness of two antimicrobial substances (for example, two mouthwashes) on the growth of a harmless bacterium. Include the method, control variables, safety precautions, and how you would analyse the results.

Explain why bacterial cultures in school laboratories are incubated at 25 °C rather than 37 °C.