Question 1: What is Salmonella and how does it cause illness in humans?

Answer: Salmonella is a type of bacteria that infects the intestines, causing food poisoning. It causes illness by invading intestinal cells and producing toxins that lead to symptoms like diarrhoea and fever.

Question 2: Describe the primary route of transmission of Salmonella bacteria to humans.

Answer: Salmonella is primarily transmitted through the ingestion of contaminated food or water, especially undercooked poultry, eggs, and sometimes raw vegetables contaminated during handling.

Question 3: Explain the role of hygiene in preventing Salmonella infection.

Answer: Good hygiene practices, such as washing hands thoroughly after handling raw foods, cooking food properly, and avoiding cross-contamination, reduce the risk of Salmonella bacteria spreading and infecting individuals.

Question 1: A food sample contains 1500 bacteria of Salmonella. If one bacteria divides every 20 minutes, how many bacteria will there be after 2 hours? (Use the formula: N = N₀ × 2^(t / d), where N₀ is initial bacteria, t is time in minutes, d is doubling time in minutes).

Answer: Initial bacteria (N₀) = 1500; doubling time (d) = 20 minutes; time (t) = 120 minutes. Number of bacteria after 2 hours = 1500 × 2^(120 / 20) = 1500 × 2^6 = 1500 × 64 = 96,000.

Question 1: Design a basic experiment to test whether a new food product is contaminated with Salmonella. Include the key steps and safety precautions.

Answer: To test for Salmonella contamination, collect a sample of the food and inoculate a sterile culture medium suitable for Salmonella growth, such as XLD agar. Incubate at 37°C for 24-48 hours. Observe for characteristic colonies. Use sterile techniques to prevent cross-contamination and wear protective gear to ensure safety. Confirm positive results with biochemical tests or PCR if necessary.

Question 2: Identify three variables you would control and three variables you would measure in this experiment.

Answer: Controlled variables: incubation temperature, type of culture medium, sample size. Measured variables: number of bacterial colonies, time taken for colonies to appear, size of colonies.

Question 1: A laboratory tests 50 food samples for Salmonella. 8 samples test positive. Calculate the percentage of contaminated samples and interpret what this implies about food safety in this context.

Answer: Percentage contaminated = (8 / 50) × 100 = 16%. This indicates that a significant proportion of the food samples are contaminated, highlighting the need for improved hygiene and food handling practices.

Question 1: Describe the process by which Salmonella bacteria invade the human intestinal lining and cause disease. Include the roles of toxins and immune response. (6 marks)

Answer: Salmonella bacteria enter the body through contaminated food or water. They survive the stomach’s acidic environment and reach the intestines, where they invade the epithelial cells. The bacteria produce toxins that damage the intestinal lining, leading to inflammation and diarrhoea. The immune system responds by sending white blood cells to fight the infection, which can cause further tissue damage and symptoms like fever. The bacteria’s ability to invade cells and produce toxins is key to its pathogenicity.

Question 1: Suggest three measures the food industry can implement to reduce Salmonella contamination in poultry products.

Answer: Implement strict hygiene and sanitation protocols, ensure thorough cooking of poultry, and regularly test products for Salmonella before distribution.

Question 2: Discuss how advancements in molecular biology, such as PCR, have improved detection of Salmonella in food safety testing.

Answer: PCR allows rapid, sensitive, and specific detection of Salmonella DNA in food samples, reducing false negatives compared to traditional culture methods. This technology enables quicker response to contamination, improving food safety and protecting public health.