Worse followed.

The woman's doctors knew how to stem her gangrene. They knew how to maintain her on dialysis too. But they'd failed to keep a microbe called Staphylococcus aureus from invisibly contaminating the woman's dialysis catheter, as well as the ulcers on her foot. The bugs proved resistant not only to every drug in the penicillin family--by now, penicillin-resistant infections in hospitals have become routine--but also to all variants of methicillin, a drug once touted as the replacement for penicillin. Grimly, the woman's doctors gave her their standard drug of last resort: intravenous vancomycin.

This time, the nightmare that doctors around the world had been dreading for more than a decade came true. Vancomycin failed completely. If the bug could not be stopped, it would infect the woman's bloodstream, attacking her vital organs and causing high fever, plummeting blood pressure, systemic infection, and ultimately, death.

To many doctors who read the tersely worded news in a July bulletin from the Centers for Disease Control and Prevention, the Michigan case was a harbinger of a future in which antibiotics increasingly may not work, a future very much like the pre-penicillin past, when unstoppable infections killed the majority of seriously ill hospital patients. In that dark past--which ended only 60 years ago--S. aureus was the bug that reigned supreme. Today, among the hospital bacteria that prey on weakened patients like the Michigan woman, it remains the most aggressive and lethal, the most widespread, and among the fastest to develop resistance to each new antibiotic.

Bugs like S. aureus roam hospitals freely, spreading by contact on the hands of a doctor or nurse, on a stethoscope or a bed railing. The more resistant they become, the greater the threat. Strict hygiene can prevent their spread, but few hospitals manage to maintain it, especially in busy intensive-care units and operating rooms. A lengthy investigative report in the Chicago Tribune this summer concluded that half of doctors fail to adhere to clean-hand policies established by the Centers for Disease Control.

Hospitals typically veil deaths from such infections in generalities. When an obituary reports the cause of death as "complications from surgery," it most likely means multi-drug-resistant S. aureus. The CDC reckons that of ten million Americans entering hospitals each year, 40,000 will die as a result of bacterial infections contracted during their stay--as many as die in car wrecks and twice the number who die of AIDS. S. aureus accounts for the bulk of those hospital deaths.

Many victims are old, with chronic conditions that weaken their immune systems. Trauma patients--victims of car crashes or bad burns--are also especially vulnerable, as are cancer patients in for radiation or chemotherapy, and newborns. But anyone entering a hospital for surgery can get it, a weekend athlete in for a knee repair, say, or an otherwise healthy person in for a bypass.

With the emergence of vancomycin-resistant staph, the danger is sure to get worse. Pharmacists have no new antibiotic that is as broadly effective as vancomycin. Traditional sources of antibiotics are tapped out, and new ones from the genomics revolution are at least five years away. The brightest hope may not be an antibiotic at all, but a vaccine from an obscure biotech company called Nabi Biopharmaceuticals, in Boca Raton, Fla. But even that is a couple of years off--scant reassurance for anyone entering a hospital today.

To battle-weary doctors and research scientists, S. aureus sometimes seems like a demonic adversary. Seen through a microscope, its round cells look like inviting golden grapes--hence the name, an amalgam of the Greek words staphule (bunch of grapes) and kokkos (grain) and the Latin aureus (golden). Usually S. aureus lives unnoticed on our skin or in our noses; a third of us are colonized with it. But once the bug reaches the bloodstream of an immunocompromised host, it infects one organ after another, causing them to fail. Often, as if intuiting its prey's weakest spots, it seeks out the heart and the brain, both difficult-to-reach sites for antibiotics, or the lungs, where it causes pneumonia. It can also cause bloodstream infections, dispatching toxins like so many torpedoes and causing the immune system to overreact in a cataclysm of toxic shock.