If you get cash from a New York City ATM, you're liable to withdraw more than just new bills. Just like the city's subway, which harbors a community of bacteria more varied than the population of the city above, the city's ATM keypads are teeming with microbes from food, human skin, and possibly even new specially adapted organisms. Taken together, the pattern of these organisms makes up a kind of dirty DNA of the city.
The researchers behind this study of crud come from New York University. The team collected microbial swabs from the keypads of ATMs in Manhattan, Queens, and Brooklyn, and cultured them back at the lab. The majority of bacteria came from "taxonomic groups known to be associated with human skin communities," but the scope of this array of organisms proved too much for the standard tools used to identify them. "SourceTracker analysis was unable to identify the source habitat for the majority of taxa," says the report.
By identifying the microbes, the NYU researchers could work out where they came from. Most of the sources were from homes: TV, restrooms, kitchen, and pillows were common—all places that collect household bacteria and transfer it to our hands. Food residues varied by neighborhood, with bony fish, shellfish, and chicken residue found in various parts of the city. This may point to specific local biomes which vary geographically.
So where were the dirtiest ATM keypads? In other words, which machines should you avoid if possible? Laundromats and stores are the worst, and as those places aren't in themselves dirty, or havens for unhygienic people, we can assume that they just don't get cleaned that often.
The most prominent microbe found on the keypads? Lactobacillales, probably from "decomposing plants or milk products." In Manhattan, there was a concentration of X. bisporus, associated with spoiled cakes and other baked goods. The researchers posit that this is down to the high number of commuters in the area, "where there are many nearby convenience stores and cafés selling this type of food product to business workers."
In retrospect, it's no surprise that a keypad stabbed by hundreds or thousands of unwashed fingers every day would become a hive of filth if left uncleaned. The proper solution is for the owners and operators of these machines to sanitize them regularly. That's unlikely, though, so you should probably just avoid ATMs in laundromats and convenience stores, and wash your hands often. Or I guess you could keep one of those little rubber money-counting thimbles in your pocket, although when you slip a nubbed rubber tip onto your finger you might get some weird looks. Then again, it's New York, so maybe nobody will pay you any attention.