Certain strains of bacteria can shut down their metabolic functions when trouble comes. They're called persisters. They are genetically identical to their non-persister brethren, but they're nastier. Although they're produced in low numbers, they're able to hide out for weeks or months in a patient being treated with antibiotics. Once they come 'back to life,' they re-start the infection. Once they're in, only patience, persistence, and luck can eventually eradicate them. Recently their luck took a turn for the worse. Researchers discovered a weakness: persisters have a sweet tooth.
Adding some ordinary sugar to the antibiotic helps it kill off persisters. Bacteria, persister and not, feed on sugars. Persisters survive by shutting down their metabolism when antibiotics strike, but if they're stimulated by sugar, they just keep feeding. This allows the antibiotics to destroy them exactly the way ordinary bacteria are destroyed.