A minor-league pitcher in his younger days, Richard Armbruster kept playing baseball recreationally into his 70s, until his right hip started bothering him. Last February he went to a St. Louis hospital for what was to be a routine hip replacement.

By late March, Mr. Armbruster, then 78, was dead. After a series of postsurgical complications, the final blow was a bloodstream infection that sent him into shock and resisted treatment with antibiotics.

“Never in my wildest dreams did I think my dad would walk in for a hip replacement and be dead two months later,” said Amy Fix, one of his daughters.

Not until the day Mr. Armbruster died did a laboratory culture identify the organism that had infected him: Acinetobacter baumannii.

The germ is one of a category of bacteria that by some estimates are already killing tens of thousands of hospital patients each year. While the organisms do not receive as much attention as the one known as MRSA – for methicillin-resistant Staphylococcus aureus – some infectious-disease specialists say they could emerge as a bigger threat.

That is because there are several drugs, including some approved in the last few years, that can treat MRSA. But for a combination of business reasons and scientific challenges, the pharmaceuticals industry is pursuing very few drugs for Acinetobacter and other organisms of its type, known as Gram-negative bacteria. Meanwhile, the germs are evolving and becoming ever more immune to existing antibiotics.

“In many respects it’s far worse than MRSA,” said Dr. Louis B. Rice, an infectious-disease specialist at the Louis Stokes Cleveland V.A. Medical Center and at Case Western Reserve University. “There are strains out there, and they are becoming more and more common, that are resistant to virtually every antibiotic we have.”

The bacteria, classified as Gram-negative because of their reaction to the so-called Gram stain test, can cause severe pneumonia and infections of the urinary tract, bloodstream and other parts of the body. Their cell structure makes them more difficult to attack with antibiotics than Gram-positive organisms like MRSA.

Acinetobacter, which killed Mr. Armbruster, came to wide attention a few years ago in infections of soldiers wounded in Iraq.

Meanwhile, New York City hospitals, perhaps because of the large numbers of patients they treat, have become the global breeding ground for another drug-resistant Gram-negative germ, Klebsiella pneumoniae.

According to researchers at SUNY Downstate Medical Center, more than 20 percent of the Klebsiella infections in Brooklyn hospitals are now resistant to virtually all modern antibiotics. And those supergerms are now spreading worldwide.

Health authorities do not have good figures on how many infections and deaths in the United States are caused by Gram-negative bacteria. The Centers for Disease Control and Prevention estimates that roughly 1.7 million hospital-associated infections, from all types of bacteria combined, cause or contribute to 99,000 deaths each year.

But in Europe, where hospital surveys have been conducted, Gram-negative infections are estimated to account for two-thirds of the 25,000 deaths each year caused by some of the most troublesome hospital-acquired infections, according to a report released in September by health authorities there.