Bugs With New Bite

TOOTH FILLINGS HAVE BEEN ACCUSED OF EVERYTHING from picking up radio transmissions to causing learning disabilities. Now comes another charge that could stick: fillings may be partly to blame for the growing problem of antibiotic-resistant bacteria.

The real villain is the mercury that makes up about 50% of dental amalgam. In a study reported in the journal Antimicrobial Agents and Chemotherapy, monkeys with mercury fillings showed a jump in drug-resistant bacteria from 9% to 70%; when the fillings were removed, resistance dropped to 12%. It seems the genes that protect bacteria from mercury lie close to those that protect against antibiotics, so bugs that survive one tend to survive the other.