For 70 years war has been waged against harmful bacteria using antibiotics. Bacteria are fighting back and today more and more bacterial infections are becoming resistant to antibiotics. Drug-resistant superbugs are spreading, and not just MRSA, but also TB, pneumonia and E coli. In Britain, hundreds are already dying of these infections, mainly the very young or the frail and elderly. Experts warn that unless the problem is solved, by 2050 there will be a massive health crisis with over 10 million people dying of resistant-bacterial infection every year. Dr Michael Mosley goes in search of the causes of the crisis and new solutions to overcome it, and asks: Have we caused the resistant superbug crisis by overusing antibiotics?