Antibiotics and infection controlEdexcel International A Level Biology: Subtopic test

1. 1
   A hospital laboratory compares two antibiotics on separate cultures of the same bacterium. When antibiotic X is added, the number of living bacteria stops increasing but does not fall. When antibiotic Y is added, the number of living bacteria falls rapidly.

   (a)

   Which term describes antibiotic X?

   [1 mark]

   • ABacteriostatic
   • BBactericidal
   • CAntiviral
   • DAntigenic

   (b)

   Why might doctors prefer antibiotic Y for a patient with a very weak immune system?

   [1 mark]

   • AIt stimulates the patient to make more antibodies
   • BIt only stops bacteria dividing, so the immune system is not needed
   • CIt kills the bacteria, so recovery does not depend on the patient's immune system
   • DIt is a vaccine that gives long-term immunity

   (c)

   Explain how a patient with a healthy immune system could still recover from an infection treated with antibiotic X.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student spreads a culture of a harmless bacterium evenly over nutrient agar in a Petri dish. She places on the surface four paper discs, each 6 mm in diameter, soaked in antibiotic P, antibiotic Q, antibiotic R and sterile water. All antibiotic solutions have the same concentration. She tapes the lid on, inverts the dish and incubates it at 25 degrees Celsius for 48 hours. The clear zones around the discs measure 18 mm for P, 6 mm for Q, 24 mm for R and 6 mm for sterile water.

   (a)

   Which antibiotic was most effective against the bacterium?

   [1 mark]

   • AP
   • BR
   • CQ
   • DSterile water

   (b)

   Why did the student incubate the dish at 25 degrees Celsius rather than 37 degrees Celsius?

   [1 mark]

   • ABacteria cannot grow at 37 degrees Celsius
   • BAntibiotics are denatured at 37 degrees Celsius
   • C25 degrees Celsius kills the weakest bacteria
   • DPathogenic bacteria grow best near body temperature, so a lower temperature reduces the risk of growing them

   (c)

   Calculate the area of the clear zone around antibiotic R. Use the formula area = pi r squared, and give your answer in mm squared.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   On a hospital ward, six patients developed infections with MRSA, a strain of Staphylococcus aureus that is resistant to methicillin. Investigators found the bacterium on the hands of some staff and on bed rails.

   (a)

   Suggest three measures that could reduce the spread of MRSA on the ward, and explain how each would help.

   [3 marks]

   (b)

   Explain how the use of antibiotics in hospitals has led to MRSA becoming common.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A patient in hospital was given a broad-spectrum antibiotic for a chest infection. Five days later he developed severe diarrhoea caused by Clostridioides difficile, a bacterium that forms resistant spores and is not killed by this antibiotic. The hospital has a code of practice for antibiotic prescription and for infection control.

   (a)

   Explain why the patient developed a Clostridioides difficile infection after taking the broad-spectrum antibiotic.

   [6 marks]

   (b)

   Discuss how a code of practice for antibiotic prescription and for infection control could reduce the spread of antibiotic-resistant bacteria in hospitals.

   [6 marks]

   Total for question 4: 12 marks

End of questions