MRSA and C. difficile are resistant bacterial strains which cause life-threatening infections in hospitals. Explain how MRSA/ C. difficile could arise from non-resistant bacteria. [6 marks]

Natural SelectionCompetition for survival between bacterial colonies/ Selection pressure is survivalVariation between colonies linking to phenotype of resistanceSpontaneous mutation produces antibiotic resistance gene/alleleAntibiotic resistance gene is advantageousThose bacteria with the gene survive and reproduce/ Survival of the fittestOffspring inherit gene and so express resistance phenotypeOver time/ after many generations, this process repeats until most of the bacteria in the population are resistantEach point is worth 1 mark. Must have 2,4,6,7 to score full marks, if not 4 marks max.