The bodies of two 19th century Arctic explorers -- found frozen in ice after nearly 150 years and so well preserved that their clothes were intact and their cheeks still had stubble -- may yield important clues about how bacteria become resistant to antibiotics.

From the explorers' intestines, microbiologist Kinga Kowalewska-Grochowska and her colleagues at the University of Alberta in Canada were able to recover and grow bacteria of the genus Clostridia, which normally live in the gut.

Kowalewska-Grochowska said that these may be the longest-dormant bacteria ever revived.

More surprising was the discovery that the bacteria are resistant to clindamycin and cefoxitin, two antibiotics.

Neither drug was developed until more than a century after the men died.

Modern strains of the same bacteria did not become resistant to these particular antibiotics until after the drugs were introduced. "Resistance of preantibiotic-era bacteria to antibiotic agents is a completely unexpected finding," she said.

"But we're working completely in the dark, because nobody has looked at bacteria this old before."

The issue is important because bacteria resistant to antibiotics can be deadly to people whose immune systems are too weak to fight off the bugs, such as AIDS patients.

The explorers had high levels of lead in their bodies, and Kowalewska-Grochowska said that fact may have caused the bacteria to develop resistance.

Some researchers have speculated that bacteria that become resistant to heavy metals may also become resistant to antibiotics.

Kowalewska-Grochowska presented her findings at the Interscience Conference on Antimicrobial Agents and Chemotherapy this spring.