You've heard that dollar bills can harbor trace amounts of drugs. If only that were the worst of it.

But those greenbacks in your wallet are also teeming with life. Each dollar bill carries about 3,000 types of bacteria on its surface. Most are harmless. But cash also has DNA from drug-resistant microbes. And your wad of dough may even have a smudge of anthrax and diphtheria.

In other words, your wallet is making you a walking petri dish. And currency may be one way antibiotic-resistant genes move around cities, says biologist Jane Carlton, who's leading the Dirty Money Project at the New York University.

Made from plastic, Canadian $100 bills are resistant to liquids and tearing. But are they better than cotton-based bills at keeping dangerous bacteria at bay? Credit: Mark Blinch/Reuters /Landov

Dirty Money: A Microbial Jungle Thrives In Your Wallet by Michaeleen Doucleff, NPR Blogs