Bacteria, Where Would We Be Without You? Without bacteria, we probably wouldn't be here. Infections can help as well as harm us. Joe Palca talks about infection — both the good and the bad — with researcher and writer Gerald Callahan, the author of Infection: The Uninvited Universe.

Bacteria, Where Would We Be Without You?

Bacteria, Where Would We Be Without You?

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Without bacteria, we probably wouldn't be here. Infections can help as well as harm us. Joe Palca talks about infection — both the good and the bad — with researcher and writer Gerald Callahan, the author of Infection: The Uninvited Universe.

JOE PALCA, host:

This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Joe Palca. Ira Flatow is away.

Infectious diseases are never far from the headlines, avian flu and E. coli here, malaria and cholera in the developing world, AIDS and tuberculosis nearly everywhere. And while we fear infection - and with good reason - if we weren't infected, we wouldn't be alive, at least not for very long.

Up first this hour we'll take a look at infections and what they do to us and what they can do for us. Let me introduce my guest. Gerald Callahan is the author of "Infection: The Uninvited Universe," just out by St. Martin's Press. He's an associate professor in the departments of pathology and English at Colorado State University. He joins us from KGNU in Boulder, Colorado. Gerry, thanks for being on the program.

Professor GERALD CALLAHAN (Author, "Infection: The Uninvited Universe"; Pathology, English, Colorado State University): Thanks for the opportunity, Joe, and good afternoon.

PALCA: Good afternoon to you. And we'd like to hear from you. If you - this is kind of a peculiar topic. I mean, if you're not expecting it, it sort of runs against the grain to think of bacteria as our friends. But I think you'll find that they are and it's worth hearing about.

Anyway, our number is 1-800-989-8255, that's 800-989-TALK. And if you want more information about what we'll be talking about this hour, go to our Web site at, where you'll find links to our topic.

And actually, Gerry, just before we get started, because I feel obliged to say this, we've known each other for about 30 years. We go back to when we were both working at Scripps Clinic in La Jolla, and so you know, if - I won't say those terrible things you did, if you'll do the same for me.

(Soundbite of laughter)

Prof. CALLAHAN: I promise to keep that to myself, Joe.

PALCA: OK, all right. So OK, I think I set up the premise here, and I hope it's right. I mean, basically your book is saying, hey, wait a minute, bacteria, viruses, don't think of them as bad, bad, bad. Why not?

Prof. CALLAHAN: I think that, first of all, one of the things that is poorly recognized is what an influence bacteria have on everything. You know, it's estimate there's something like 10 to the 29th bacteria on this planet. At best, there's only something like what, 10 to the 10th people. That means they outnumber us a trillion to one. Everything is coated with bacteria, and it's been part of our evolutionary history. And without them, we're not us.

PALCA: So are these - I mean - are these bacteria important historically? In other words, genes came from bacteria once upon a time. Or is this something that, you know, on our day-to-day life, bacteria are doing something good for us?

Prof. CALLAHAN: I think that there is some evidence that there have been bacterial genes transferred in. That remains somewhat controversial. But on a day-to-day basis, the bacteria that inhabit our skin and our gut, and all the other parts that are exposed to the environment, are doing us lots of good. They're producing things we need. They're running part of the show. They actually control several hundred human genes.

PALCA: So what's the - I mean, what makes a good bacteria go bad? Or put another way, I mean are there - I mean, for example E. coli. That's a good example. I mean, there's E. coli all over our gut, as I understand it, but you know, there are bad kinds of E. coli. So how does our body figure out which is which?

Prof. CALLAHAN: That's a question that immunologists are still struggling with, Joe. I mean, that is a major question, because a lot of diseases seem to arise from the process of the body forgetting which are the good and which are the bad diseases like - both Crohn's disease and Colitis result from the fact that the immune system seems to get involved and start inflammation where it shouldn't.

Normally, we don't recognize those things as foreign. There's just - there's no simple answer to that question.

PALCA: And are there bacteria that would be OK if they're on the skin but would be bad for you if they got into your lungs?

Prof. CALLAHAN: Absolutely. And although the upper parts of our lungs are normally inhabited by bacteria, the lower part of the lungs are not, and not only lungs but in the blood. You brought up one example, E. coli, which all of us live with every day.

E. coli in the blood is a major problem, though. It's a real threat, any sort of substance like that. So yeah, lots of different things can cause problems when they get in the wrong spot.

PALCA: So here's the other thing that puzzled me. So you've got these bacteria that you need and that help you out and do good things for you, and then you get a bacterial infection, which is clearly not doing a good thing. So you go to the doctor, you get an antibiotic - hopefully, you do have a bacterial infection and not a viral one. But anyway, does it kill all the bacteria in your body and you have to get them all back, or does it specifically kill the ones that are causing - making you ill?

Prof. CALLAHAN: There is no antibiotic that is sufficiently focused to just act on those bacteria that are causing problems. Even those of the narrowest spectrum will kill whole groups of bacteria. And wide-spectrum antibiotics that we often get will wipe out everything and you've got to start over almost from zero.

PALCA: Right. So yeah, so if the bacteria are good for us and we take an antibiotic that wipes out everything, is it possible that we're, you know, curing one problem and causing another?

Prof. CALLAHAN: Well, I think especially you might ask that question of women, but it's also true to some extent of men about how often yeast infections follow taking a wide-spectrum antibiotic.

Normally, the bacteria not only occupy the space the yeast would like to colonize, but they also produce factors that slow down the growth of the yeast. Once they're gone, the yeast just take over.

PALCA: Right. You talk in the book about some diseases that you think are related to bacteria that I think most people wouldn't necessarily think of as being related to bacteria. Can you give an example of that?

Prof. CALLAHAN: There's a whole series of things that fall under the heading of what we normally call chronic diseases - certain types of cancer, certain types of heart disease - that appear to have at least an element that's involved with an infectious agent.

Schizophrenia is another one. Schizophrenia is more common in children whose mothers had flu or other viral infections during the second trimester. There's evidence of a higher incidence of a particular virus called Borna disease virus found in people at autopsy that have died from mental disorders.

So there's a whole series of things. I think it may turn out that the disease that has no infectious component may well be the exception, not the rule.

PALCA: And does this - I mean, this must represent a change in thinking.

Prof. CALLAHAN: It certainly does. I mean, what started it - I think what really started people re-examining things was the issue with ulcers and Helicobacter pylori. You know, we've always been told that ulcers were caused primarily by stress and maybe taking too many aspirin and some things like that, and certainly those factors do seem to play a role.

But often if you treat people with ulcers with an antibiotic, they get better, and it's because of a bacterium called Helicobacter pylori that begins to colonize the stomach lining and actually digest and eliminate part of that lining as a result of infection.

Once people realized that this disease that everyone has always assumed was unrelated to infectious agents was clearly involving a bacterium, that sort of changed everyone's thinking. And a lot of things are being examined more critically now for infectious agents.

PALCA: But it seems to me that - I went to a conference now I guess 20 years about viral-associated cancers, and so the cancer-virus link has been around for a while.

Prof. CALLAHAN: That's true, and it's surprising in some ways that it hasn't drawn more attention. The most obvious cases, I think, being of Kaposi's Sarcoma and some of the lymphomas that show up in AIDS patients.

Certainly, the Kaposi's Sarcoma is a Herpes-virus infection that's causing that. And perhaps we don't pay too much attention to that because that's only in people with severely suppressed immune systems, but also it looks like some lymphomas and perhaps some leukemias may be viral in origin too. For reasons that aren't clear to me, that seems like that's kind of been set aside as the exception, not the rule.

PALCA: Interesting. Well, as I thought, there's a lot of interest on this. The phones are blinking away. So let me - let's go to the calls now and take one from Erica(ph) in Tallahassee, Florida. Erica, welcome to SCIENCE FRIDAY.

ERICA (Caller): Hi, thanks.

PALCA: What's your question?

ERICA: On the helpfulness of bacteria, I'm the mother a 9-month-old and I've been keeping her at home. And I have a friend who has hired a nanny because she was told by her pediatrician that too much infection before the first year - exposure to bacteria - actually weakens the child's body and doesn't serve to strengthen the immune system. I'm wondering if you could speak on that?

PALCA: OK, Erica. Thanks for that question. Gerry, what about that?

Prof. CALLAHAN: The most recent study I saw shows actually a direct correlation between the age at which a child enters preschool and the decrease in their likelihood of developing both allergies and asthma. It appears that early exposure is a normal part of existence and that if we overprotect during that time there's a real risk of having consequences because of that.

PALCA: Yeah, because there has been - people have been scrambling around to come up with an explanation for why this sort of alarming rise in asthma, especially in inner cities, and maybe this is part of it.

Prof. CALLAHAN: There's a great deal of evidence now to suggest the lack of infection during early childhood directly correlates with the probability of developing an allergy or asthma. In fact, you can even show that there's a direct correlation between the educational level of parents and the likelihood that their children will have allergies or asthma because they tend to live better, they tend to be more protective, those sorts of things. And without that early infection it changes the immune system.

PALCA: Interesting. Let's take another call now and go to Sam(ph) in Tucson, Arizona. Sam, welcome to SCIENCE FRIDAY.

SAM (Caller): Thank you for taking my call. My question is about - I saw a study a little while ago that didn't really make sense to me about bacteria effecting weight gain, saying they had given mice some bacteria and given mice some other bacteria in their stomach and some gained weight and some didn't. Does that have application to humans? Did I get it right?

PALCA: OK. Sam, let's ask Gerry. What do you think, Gerry?

Prof. CALLAHAN: I have seen studies in mice where they have looked at issues of weight gain and obesity in mice. Starting the mice out with no infection made them much more at risk later on when they were re-infected for rapid weight gain. I don't know of any studies in humans.

PALCA: It seems to me, though, I've read that there have been people who've been trying to address this question about the - you know, the kind of bacteria in the stomach and whether that may or may not have something to do with how much weight a person will - or how efficient it is that he or she is digesting food and things like that.

Prof. CALLAHAN: You know, it makes complete sense because the normal flora, the bacteria that inhabit the stomach and the intestine, in each of us is different. Even those of us who grow up in the same household, eat the same food, breath the same air end up with a population of bacteria that are unique, almost as unique as our genetic imprint. And obviously one of the things the bacteria are involved with in certainly another species, and probably in humans too, is aiding in aspects of digestion, increasing the efficiency of digestion of cellulose, for example - lots of things that could cause an increased caloric addition to a person's diet that the rest of us wouldn't get.

PALCA: Sam, thanks very much for that question. Just very quickly - we have only a few seconds before the break - but there are genes that bacteria are switching on and off that could be effecting people's health, isn't that right?

Prof. CALLAHAN: That is right. Somewhere in the range - it's estimated somewhere in the range of one or 200 genes of ours are under the control of bacteria. That may not seem like a huge number, but when, you know - the genome study should say we've only got about 30,000. That's approaching, you know, a percent, so it's significant.

PALCA: OK. All right. Well, Gerry, we have to take a short break but we'll come back and talk some more about infection and also look at a new - an early warning system for infectious disease outbreaks around the globe. Stay with us.

(Soundbite of music)

PALCA: From NPR News.

(Soundbite of music)


We're talking this hour about why - about infections with my guest, Gerald Callahan. He's the author of "Infection: The Uninvited Universe." He's a professor in the Department of Pathology and the Department of English at Colorado State University. That's actually a kind of an interesting mix, Gerry. How did you wind up getting a joint appointment like that?

Prof. CALLAHAN: Some time ago - actually, it began when my wife signed me up for a poetry course one time, and I became very interested in writing. And as it develop, I developed a stronger relationship with the English Department and they found the sorts of things I was writing more interesting. On the other hand, my department - the Pathology Department - found it harder and harder to figure out whether I was doing anything at that time. So, one of the things that was suggested was that I consider a joint appointment and I could be evaluated by the two different departments as well as participate in classes for both of these departments. And it's really worked out very well.

PALCA: So, I mean, just as we're on this topic, briefly, you know - how - what do you think? There's been historically - scientists who are good communicators tend to be slammed by their colleagues because, you know, they're good communicators, therefore they can't be good scientists. What do you think about that argument?

Prof. CALLAHAN: Yeah, the classic example of that is Carl Sagan, I guess, and what happened with the National Academy.

PALCA: Yeah.

Prof. CALLAHAN: I think that one of the shortcomings of science and one of the difficulties of selling science to the public - the people who actually foot the bill - is the lousy job of communication that we as scientists have done. And I think science can only benefit from people who can more effectively share the real wonders of science - things like what you do, Joe, and what I've had an opportunity to do. I think they're critical.

PALCA: We're talking with Gerry Callahan, who, in addition to being a pathologist or an immunologist, as I know he started out as, and a writer, he's someone I've known for 30 years because we had the fortune or misfortune - I'm not sure which - of working together a long time ago. But you're welcome to join the conversation. Even if you didn't work with Gerry 30 years ago, you're welcome to talk to us. Number here is 800-989-8255. That's 800-989-TALK. And let's take another call now. How about if we go to Larry(ph) in Durham, North Carolina, I assume that is. Larry, welcome to the program.

LARRY (Caller): Thank you.

PALCA: What's your question?

LARRY: My question is: Do you think that vaccines should be given to children at a later stage instead of the normal starting at eight weeks?

PALCA: Gerry, is that - are you able to address that?

Prof. CALLAHAN: I mean, I think it's important for me to say up front that I am not a physician and my studies have focused a lot on animals, and I would never presume to make a recommendation. With my own children I felt that it was important to start that early, and I think that it's - the thing about vaccination is that it is, in effect, an infection and it strengthens the immune system. And that phase - that early phase when kids - you know, the moment kids leave the womb they're confronted with all kinds of infection.

The little bit of additional stress that may be put on the immune system by vaccination at that point doesn't seem to me to warrant - it didn't I my case warrant my deciding not to vaccinate my children according to the schedule.

PALCA: Let's take another call now and go to - how about - let's see, Jeremy(ph) in Ford Lauderdale - I guess that must be Florida. Jeremy, welcome to the program.

JEREMY (Caller): Yes it is. Thank you for having me on here. I'd really like to go into the conversation that you just had about the vaccines. But my question refers to the controversial statement that he - that Gerry made in the beginning about bacteria from the beginning. And I was wondering if he was referring to mitochondria, and if so, could he please tell me what kind of controversy it is or, like, the argument for or against.

PALCA: Let me - so Gerry, I'd like to hear that answer. But remember, we have to describe what a mitochondria is, first of all.


Prof. CALLAHAN: I'm not completely certain I understand the question.

JEREMY: (Unintelligible) in the cells. I'm sorry (unintelligible).

PALCA: OK, I think I understand the question. What he basically is asking - you know, I've read and I think you mention in the book that mitochondria - I'll explain - Mitochondria, they call them the power plant of cells. They're little sort of organelles. They're little cells inside of cells, essentially. They have their own DNA and they're the part of the cell that makes the energy, the ATP that fuels the chemical reactions inside the cell. And the question is: Were these once in fact bacteria and mammalian cells sort of scooped them up and used them for their own purposes? And that's I think what the question was getting at.

Prof. CALLAHAN: Yeah, and I think that the evidence says that these were once free-living bacteria. And in my mind they're still bacteria, they're just not free-living any longer. They replicate on their own schedule, they have their own genes, as you said. They have their own (unintelligible), et cetera, that look - all of which look very much like bacterial components. And it's even been argued by some people who studied it more carefully that I that maybe all of the cellular organelles represent at some level some interaction with another organism at some point.

But I'm pretty comfortable about mitochondria and chloroplasts, the similar sorts of organs that work in plants that convert sunlight into sugar.

PALCA: What does - if you take that point of view, instead of looking at them as parts of mammalian cells but bacteria that are sort of captured but retain some identity, what does that do to your thinking about what it means to be a human being?

Prof. CALLAHAN: Yeah, I think that that's a wonderful question, and I think that's been the most interesting part of doing this work all together. I don't think of myself anymore as something apart from all the rest of it. I think that there are many different living things that go into making up one thing that we like to call humans, but much of it's beyond any level of control that I have. And I'm more of an ecosystem than an individual.

PALCA: But are there things - I mean, you would - I mean, in development, in evolution, there's a constant changing and altering of the human genome. So how do you think of the difference between genes that were sort of performing a function in a bacteria that were sort of taken into the human genome and become part of what is human in an evolutionary sense, versus a free-living organism that could be set off on its own? In other words, when do we own the genes and when are we just borrowing them?

Prof. CALLAHAN: Yeah, that's a great question. There are - mitochondria had continued to shift genes into the human genome along the way, in some ways maybe economizing. But in a sense that sort of a question in my mind like asking: Which of the ants in the anthill are really part of the whole thing? It takes it all for it to function. And the biggest impact on our genome has been viral effects over the years, all kinds of changes in the human genome that were caused by viruses. And I think it's hard to separate ourselves from those infections in a way that is biologically sensible.

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