Antibiotics & antibiotic resistance

Antibiotics are the medicines that fight bacterial infections, and this lesson explains exactly how they work — and why they are now under threat. We follow penicillin, the very first antibiotic, and see how it blocks the enzymes that build the bacterial cell wall out of peptidoglycan, so that a growing bacterium ends up with a weak wall and bursts by osmotic lysis. We then answer two questions people often get wrong: why antibiotics do nothing against viruses (which have no wall, ribosomes or metabolism of their own) and why they leave our own eukaryotic cells unharmed (no peptidoglycan wall, and 80S rather than 70S ribosomes) — the idea of selective toxicity. Next we tell the story of antibiotic resistance: how a chance mutation can make a single bacterium resistant, and how natural selection then lets that survivor multiply until the whole population — like the MRSA superbug — can shrug off the drug. Finally we weigh up the consequences of resistance and the steps we must all take to slow it down, and finish with the agar-plate zone-of-inhibition experiment.