Inside a third-floor office a few blocks from the Hudson River in Yonkers, N.Y., a small biotechnology company called ContraFect prepares to test a remarkable new way to kill bacteria in humans. Antibiotics, after many years of use and overuse, have lost their edge against rapidly evolving bacteria, with everything from staph infections to tuberculosis becoming more devastating, deadly and difficult to treat. Whereas traditional antibiotics have mostly been derived from chemicals produced by soil bacteria and fungi, ContraFect has found an alternative in bacteriophages: viruses that infect bacteria and hijack their internal machinery. In nature, phages produce enzymes called lysins, causing the bacteria fall to pieces and new phages to tumble out by the hundreds. ContraFect believes it can harness these lysins to treat bacterial infections in humans.