Staphylococcus aureus is thebug responsible for many hospital infections, and scientists are worried that some strains were acquiring high levels of resistance to virtually every available antibiotic.
Scientists first changed three amino acid molecules of H5N1 in a way they believed would boost the bug's affinity for human hosts, then infected ferrets with the mutated virus.
In the experiment published in Nature in May, scientists combined H5N1 and swine flu and came up with a hybrid bug that could leap from mammal to mammal.