There are up to 3,000 types of bacteria living on paper money.

This is the means of "transporting" bacteria from one person's hands to another and is a source of transmission of many dangerous diseases to human health.

By analyzing the material of a $1 bill, researchers discovered more than 3,000 different types of bacteria. This number far exceeds all previous studies that examined banknotes under a microscope to detect bacteria.

Still, researchers have only been able to identify the DNA of about 20 percent of the bacteria. The rest have yet to be catalogued in the genetic database.

Among the bacteria found on paper money, the most common are those that cause acne. Other bacteria are equally dangerous, with the ability to cause stomach ulcers, pneumonia, food poisoning, and staph infections in humans.

Some types of bacteria on paper money also contain genes that can weaken human immunity.

"We were really surprised by what we found. We even saw bacteria growing on paper money," said Jane Carlton, director of the Center for Molecular Biosciences at New York University.

Another unpublished study also offers a glimpse into just how dirty paper money can be. From rubles to euros, paper money is one of the most widely circulated forms of currency in the world. Epidemiologists have long worried that paper money is a source of disease that is difficult to control.

Philippe Etienne, director of Innovia Security Pty, who conducted a study on 23 types of banknotes from many different countries, said: "The wallet you carry with you carries your body temperature. This is the perfect petri dish for growing bacteria."

According to the US Central Bank, an additional 150 billion US dollars are circulated around the world every year. Each $1 bill is printed on a cotton-flax blend and can be used for at least 21 months.

In 2014 alone, the US Federal Reserve spent $826.7 million to print a total of $297.1 billion worth of money.

To make paper money more durable, some countries such as Canada or the kingdom of Bhutan have used polymer materials to print money with biological identification elements to increase the level of anti-counterfeiting.

In a study on the impact of banknote materials on public health, researchers at the University of Ballarat (Australia) examined the changes in 10 banknotes as they moved from supermarkets, cafes to restaurants. The study was conducted in 10 countries with the same types of banknotes in circulation.

According to a 2010 study conducted by the journal Food Safety and Pathogens, there are differences in the levels of bacteria on banknotes from different countries.

In addition, the study also showed that there were fewer bacteria on polymer money than on cotton paper money. "Money printed on polymer materials has the characteristic of being impermeable to water. This is the characteristic that makes it less likely to contain bacteria than cotton money."

In another study conducted by the Center for Antibiotic Research and Infection Control, scientists tried culturing bacteria on seven different currencies.

Research results show that there are still some types of bacteria that can survive for a long time on polymer foil.

Humans also contribute to the growth of bacteria on banknotes. Bacteria can feed on the oils or sebum on human skin as banknotes are passed from person to person.

"When you hold a piece of paper money, you're feeding the bacteria on it," said Nabil Lawandy, a physicist at Brown University who has designed security features on banknotes for more than 19 central banks.

In a study of the surface of banknotes conducted by a team of scientists from India, the Netherlands and the United States, researchers isolated 93 types of bacteria that adhere to the surface of banknotes.

In 2012, microbiologists at Queen Mary University (UK) concluded that 6% of banknotes in circulation in the UK contained e.coli bacteria at levels equivalent to a toilet seat.

In the latest study conducted by a team at New York University, researchers used DNA databases and computer analysis to quickly identify the DNA of bacteria present on paper money.

As a result, the study found many more types of bacteria than previous studies that only looked at banknotes under a microscope.

In the experiment, the researchers analyzed DNA samples from 80 one-dollar bills collected from a bank in Manhattan.

The results were 1.2 billion. This data took up 320 GB of computer storage, equivalent to the amount of space used to store all the medical documents in a library.

Half of the 1.2 billion DNA fragments collected were human. The other half belonged to bacteria, viruses, fungi, and other disease-causing biological agents.

In addition, the researchers also found small amounts of the viruses that cause anthrax and diphtheria. In addition, the research bills also contained DNA from horses, dogs, and even rhinos.

"We've found so many species on just one piece of paper," said Julia Maritz, a geneticist at New York University who has done a lot of DNA analysis.

According to Dan Tri