Good Germs, Bad Germs: Health and Survival in a Bacterial World by Jessica Snyder Sachs, is an up-to-date summary of what we know about how bacteria interact with humans.
It's a fascinating story, because after a lifetime of "fighting germs" it seems that scientists are coming to learn that the interaction between bacteria and our bodies is far more complex than was ever realized and we have to work with germs and make alliances with "good germs" in order to survive.
The book starts out with several chapters that explore in greater detail than I've seen elsewhere, the research that has been establishing "The Hygiene Hypothesis." This is the idea that the huge rise in autoimmune disease we are currently experiencing is being caused by too much cleanliness.
It is starting to look like we are not being exposed to enough of the right bacteria very early in life or as we go through our daily lives, thanks to changes in water treatment, how we get our food, how we medicate illness, and how we clean our homes.
It turns out that our bodies are complex ecosystems in which maintaining populations of billions of bacteria of various kinds is essential for preserving our health, particularly in the digestive system, where, if our population of bacteria are killed off, the digestive system fails to function properly. Children absorb the good bacteria they need to have populating their own digestive tract from birth on. A caesarian birth, for example, results in a baby who is not exposed to the bacteria found in the mother's perineal area, which raises the risk of developing autoimmune problems like asthma and Type 1 diabetes.
Children who are given antibiotics early in life which kill off the developing populations of healthful bacteria also develop more autoimmune diseases, particularly asthma.
And all of us who drink filtered water (which the book mentions was not common until the last 25 years of the 20th century) and eat packaged, preservative-filled foods, may not be maintaining the colonies of soil and fecal bacteria which our bodies depend on to regulate our immune systems and fend off dangerous bacterial invaders.
An important point that Sach's raises in Good Germs, Bad Germs, is that while in the past many people, including those opposed to vaccination, have argued that exposure to disease is required for the development of a healthy immune systems this is not, in fact, true. More recent research suggests that it is not infection with disease that protects children. Disease, is NOT good for people.
What is good for people is acquiring populations of benign non-disease causing bacteria that live on skin, on mucous membranes, and within the digestive tract. This is because these populations of benign bacteria do two things. One is that they fill up the ecological niche your body represents, making no room for the more dangerous bacteria which cause disease to move in.
The other, which is just starting to be understood, is that by their very presence, these benign bacteria send out biochemical signals that cause the immune system to respond by developing what is called "tolerance"--i.e. turning down the immune system. It is this tolerance that turns off the inappropriate immune attacks that cause asthma, diabetes, multiple sclerosis, etc. When the body is not populated by the bacteria it expects to meet, it does not develop tolerance, and instead seems to go on high alert, and unfortunately, this leads it to attack things like peanuts and pancreases.
Another interesting finding is that having the right bacteria established in your body causes changes in the cytokine mix which affect your mood. Sachs describes some research that finds that when levels of Interleukin-10, a cytokine that is secreted when tolerance develops, rise, serotonin levels surge too. The implication here is that the depression that is associated with autoimmune disease may not be psychological. Yes, it is a bummer having to deal with diabetes, but it may FEEL like a bummer because of the lack of calming chemicals in the brain.
This reminded me of one of the oddities of tuberculosis in the 19th century, which is that its victims were always described as being bizarrely cheerful especially as their condition worsened. One wonders if perhaps this had something to do with their immune systems having developed too much tolerance and pumping out serotonin happy juice. The book mentions that this kind of inappropriate tolerance can develop in the presence of some kinds of chronic infections that the immune system cannot take care of.
The good news reported in this book is that there are people working on using carefully cultured populations of benign bacteria to modulate the immune system. The bad news is that it turns out that bacteria can trade just about any trait you can think of with each other, particularly resistance to any antibiotic ever made, and they do it across species lines and very, very fast. A bad bug you pick up on your spinach can pick up a drug resistance gene from a "good" bacteria in your gut in the 3 hours it takes to hit your lower intestine.
This means that the most "healthful" bacteria in the world can go bad if you already have drug resistant bacteria haunting your gut. And unfortunately, most of us do. Much of the rest of the book is taken up with discussing the problems caused by the drug resistant bacteria that now fill our world.
One huge reason for the unstoppable growth of MRSA and other bacteria that do not respond to antibiotics is the overuse of antibiotics in animal feed. It turns out that the problem is not just residues that you might eat. The problem is that resistance genes that develop in livestock pass into the ground and get out into the world where the promiscuous bacteria trade them around continually. You don't need to eat meat to get bacteria in your gut that are resistant to antibiotics used only in cattle.
Another problem is the use of antibacterial soaps which kill off the friendly bacteria in our homes and leave a nice, big empty place for baddies to grow. Sachs compares cleaning your cutting board with antibiotic soap to nuking your lawn with Roundup without reseeding it, which ensures that you will end up ONLY with clumps of crabgrass and weeds.
There's lots more in this book that you should read if you are concerned about MRSA or worry about infection. And if you aren't concerned about MRSA, you should be!