Lloyd H. Conover, a scientist who had the simple idea of exchanging an atom in one antibiotic to create a new, better one — tetracycline — that became one of the most widely used drugs of its kind and heralded a new era in the treatment of infection, died March 11 at a retirement community in St. Petersburg, Fla. He was 93.

The cause was congestive heart failure, said his wife, Katharine Meacham Conover.

Dr. Conover helped spark a revolution in the development of antibiotics while working as a research chemist with the Pfizer pharmaceutical company in the early 1950s.

His creation, tetracycline, is used to treat conditions ranging from acne to pneumonia to Lyme disease to sexually transmitted disease. Beyond its clinical applications, the drug revealed vast new potential for man-made antibiotics.

According to the Lemelson-MIT Program honoring invention, tetracycline was “the first antibiotic made by chemically modifying a naturally-produced drug.” It eventually was used in farm animals as well as in humans.

Dr. Conover died March 11 at 93. (Family Photo)

When Dr. Conover began his career, naturally occurring antibiotics were commonly prescribed to combat bacterial infections. The best known of those drugs was penicillin — the “marvelous mold that saves lives,” as Time magazine dubbed it — discovered by the Scottish biologist and future Nobel laureate Alexander Fleming in 1928.

Dr. Conover’s insight — near-heresy at the time — was that a chemically altered version of an antibiotic might be more powerful than the existing one. To test the theory, he and his colleagues tweaked the structure of aureomycin, another common antibiotic, by replacing a chlorine atom with a hydrogen atom.

To the surprise of many scientists, the new drug did prove more effective in fighting bacteria, particularly bacteria that had developed resistance to antibiotics already in use. It also produced fewer side effects in the patient.

Reported in the Journal of the American Chemical Society in 1953, the discovery was patented in 1955 and swiftly became a mainstay of medicine, despite decades-long legal wrangling and licensing battles.

“I had essentially a second career, preparing for and giving depositions and testifying,” Dr. Conover wrote in a journal article cited by the New York Times.

Lloyd Hillyard Conover was born in Orange, N.J., on June 13, 1923. His mother was an artist, and his father was a lawyer.

After Navy service in the Pacific during World War II, he received a bachelor’s degree in chemistry from Amherst College in Massachusetts in 1947 and a doctorate, also in chemistry, from the University of Rochester in New York in 1950.

Dr. Conover served at times as Pfizer’s director of chemical research on chemotherapy and as research director at the company’s laboratory in Sandwich, England. He was credited with helping develop Pyrantel and Morantel, drugs used to eliminate worms and other parasites. He retired from Pfizer in 1984.

Dr. Conover’s first wife, Virginia Rogers Kirk, died in 1988 after 44 years of marriage. His second wife, Marie Strauss Solomons, died in 2003 after 13 years of marriage.

Survivors include his wife Katharine Meacham Conover, whom he married in 2005, of St. Petersburg; and four children from his first marriage, Kirk Conover of Little Falls, N.J.; Roger Conover of Freeport, Maine; Heather Conover of Washington; and Craig Conover of Evanston, Ill.

He also had six surviving stepchildren, Suzanne Love of Afton, Va., Virginia Karpovich of Paia, Hawaii, Walter Solomons of Sarasota, Fla., Katharine Meacham of Asheville, N.C., and Andrew Meacham and Laura Meacham Keane, both of St. Petersburg; 16 grandchildren; and seven great-grandchildren. His stepson Robert C. Meacham Jr. died in 2000.

Dr. Conover was a 1992 inductee of the National Inventors Hall of Fame in North Canton, Ohio. His innovation six decades ago, according to Lemelson-MIT, “prompted an industry-wide search for superior structurally-modified antibiotics, which has provided most of the important antibiotic discoveries made since then.”