Cells: Cell recognition and the immune system

(1) Bacteriophages, or phages, are viruses that infect bacteria. Each type of phage recognises and binds to specific proteins on the surface of particular bacterial cells. (2) Once attached, the phage injects its genetic material, which takes over the bacterial cell's enzymes and ribosomes to make new phages. (3) Within an hour the cell bursts, releasing hundreds of phages that can infect neighbouring bacteria. (4) Phages were used to treat infections in the early twentieth century, but in most countries they were abandoned after antibiotics became widely available. (5) The rise of antibiotic-resistant bacteria has renewed interest. (6) In several recent cases, patients with resistant infections that had not responded to any antibiotic were treated with a mixture, or 'cocktail', of phages chosen to match their particular strain of bacteria. (7) Critics point out that bacteria can also become resistant to phages, for example by changing the proteins on their surface. (8) Supporters reply that phages evolve too, and that a resistant bacterium is often less able to cause disease. (9) Because each cocktail must be matched to the patient's bacteria, phage therapy is difficult to test in the large, standardised clinical trials that regulators usually require.