Bacteria as pathogensEdexcel A-Level Biology B: Mind map

Exam questions on Bacteria as pathogens

1. A patient develops a red, swollen surgical wound. Swabs taken from the wound grow Staphylococcus aureus, and the bacteria are found only in the wound. Over the next day the patient develops a high fever, a rash and a fall in blood pressure. Blood tests find a toxin made by S. aureus circulating in the blood, but no bacterial cells.
   The bacteria were found only in the wound. Explain why the patient has symptoms in tissues far from the wound.2 marks
2. Several students became ill 12 hours after a barbecue, with fever, vomiting and diarrhoea. Salmonella was cultured from undercooked chicken that they had eaten. A doctor explained that part of their symptoms was caused by a component of the Salmonella cell wall that is released when the bacteria die and break open.
   A student suggests that killing large numbers of Salmonella in the gut could briefly make the symptoms worse. Explain why this is plausible.2 marks
3. A 34-year-old man has had a cough for eight weeks, with blood in his sputum, night sweats and weight loss. A chest scan shows several small rounded lesions in his lungs and areas where lung tissue has been destroyed, leaving cavities. Mycobacterium tuberculosis is cultured from his sputum. Unlike Staphylococcus aureus, M. tuberculosis does not make a powerful toxin.
   Explain how M. tuberculosis causes the lung damage seen in this patient.3 marks