The Usual Suspects: The Microorganisms that Cause HAIs

It is estimated that there are  5×10³⁰ bacteria on Earth. That's 5,000,000,000,000,000,000,000,000,000,000, or 5 nonillion. We have not even begun to identify them all, and new strains are evolving all the time. We not only coexist with bacteria on Earth, they outnumber us by such a mind-boggling degree that we cannot even conceive it. Consider this: There are currently just over 7 billion humans on earth, and one spoonful of rich soil contains approximately 10 trillion bacteria. And our bodies? Bacterial cells outnumber human cells 10 to 1. (But don't worry, you're not a zombie. They make up only 3% of our body mass. But still.)

Before these numbers make you uneasy, remember that bacteria are, on the whole, essential to our survival. They help break down plants and animals as part of the decay cycle. They help us digest our food. They recycle nutrients in the soil and air, breaking down compounds into the components other living things need to survive, including humans. Hey, they help us make cheese, yogurt, and beer.

But some bacteria are pathogenic, that is, they cause disease. Even harmless bacteria can cause disease when the right opportunity arises, such as when skin flora enter the body.  When they enter our bodies and reproduce, creating an infection, they can cause severe illness and even death. This week's posts will explore the bacteria responsible for the most common HAIs.

The 10 most common pathogens (accounting for 84% of any HAIs):

And, because it's not bad enough that there are opportunistic infections, there are also the Keyser Söze germs: Drug-resistant opportunistic infections.

16% of all HAIs were associated with the following multidrug-resistant pathogens: