Study Reveals How Bleach Wipes Out Bacteria

Researchers have figured out just how bleach kills bacteria, according to a new study in the journal Cell. Ursula Jakob, one of the authors of the paper, explains how bleach does its dirty work and how this information might be put to good use.

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IRA FLATOW, host:

Back in 1913, a handful of California entrepreneurs set up shop across the bay from San Francisco to churn out gallons upon gallons of industrial-strength sodium hypochlorite - bleach. They started out selling wagon loads of this stuff to local laundries, breweries, municipal water companies. But pretty soon, they developed a lighter concentration, household bleach, which they marketed as a cleanser and germicide. It came in small little bottles, pretty similar to the one you might have under your kitchen sink or your bathroom right now. And from the words chlorine and sodium hydroxide which together form the product's active ingredient, they came up with the company's name, Clorox.

Of course, today, Clorox and other chlorine bleaches are a common ingredient in the arsenal of household-cleaning products. We use bleach's cleaning power to sanitize our toilets, to scour the bathroom tile, to clean the kitchen. We even use chlorine in our pools to chlorinate our water. But just how does this ubiquitous product work to wipe out bacterial foes? Well, a new work in the lab may have found the answer. Joining me now to talk about that research out this week in the journal Cell is Ursula Jakob. She's an associate professor in the Department of Molecular, Cellular and Developmental Biology at the University of Michigan in Ann Arbor and she joins us today from a studio in Ann Arbor. Welcome to the program, Dr. Jakob.

Dr. URSULA JAKOB (Director, The Jakob Lab, Department of Molecular, Cellular and Developmental Biology, University of Michigan): Hello, Ira. Thank you so much for having me on the show. It's wonderful to be here.

FLATOW: Didn't we always know how bleach worked?

Dr. JAKOB: That is a very good question. We all assumed, I guess many people assumed, that we knew, and that is also the response that I now get since we have published the study, actually...

(Soundbite of laughter)

Dr. JAKOB: Oh, we didn't know how it worked. And when we started out, we did not start out our research to try to figure how bleach works. That's was not even on our horizon, I have to say. We started out working on a bacterial protein, a stress protein called Hsp33, and midway through this project, we actually stumbled onto hydrochloric acid or the active ingredient in household bleach, and we had to figure out how it works. So, that's what we did.

FLATOW: So, how does it work?

Dr. JAKOB: So, it works very similar to high temperature. So, I have to go back a little bit to explain to you what stressed us or what does - what high temperature or bleach does. It has the main or the most sensitive components in our cells, as well as in the cells of bacteria, are the proteins. And these are our workhorses, as I'm sure you know; they do everything. The muscle proteins allow us to walk, and the enzymes allow us to digest the food that we just ate here in Michigan, to get the energy. And the same is true for bacteria. So - and we have thousands of different proteins, and for these proteins to do all those different jobs, they need to have very, very specific, beautiful structures. And we know many structures of those proteins. And you can sometimes compare to houses; you know, every house has a specific structure...

FLATOW: Sure.

Dr. JAKOB: To fulfill this specific function.

FLATOW: Right.

Dr. JAKOB: And that's exactly the same with proteins. And what elevated temperatures, for instance do, when we have fever or when we incubate bacteria with the elevated temperatures, these structures, these protein structures, some of them are damaged. We call them the protein unfold. They lose this beautiful structure.

FLATOW: Because proteins need to fold in the right way for them to work.

Dr. JAKOB: Exactly, exactly.

FLATOW: So, when we heat them up or we put bleach on them, they unfold.

Dr. JAKOB: Exactly, they unfold. They lose the structure, and what they then do, they lose their function. Now, that's one problem. A much bigger problem, however, is it seems to be, at least during heat (unintelligible) as well as doing bleach stresses, that these proteins not only lose their structure, but they also start to form these large aggregates. So, when proteins unfold, they expose their core, which is a very sticky core, but it's usually surrounded by the outside, so it's not - so it doesn't matter. But when they unfold, they start to stick to other proteins that also unfold and formed these large aggregates. And this is very dangerous for the cells.

And you can compare that very nicely when you make your five-minute breakfast egg. So, you start out the egg, and then you have this liquidly egg white and yolk, and everything is liquid, and it doesn't taste very good, and you start heating it up. And within five minutes, what you do is you unfold all these egg proteins. They start to clump together; they aggregate, as we call it...

FLATOW: Right.

Dr. JAKOB: And then they form this hard mass that you can eat with a little bit of salt on top, and it tastes delicious. And so this is exactly what we found that bleach does as well; it targets these, we call them thermolabile proteins, proteins that have the tendency to unfold when you slightly rise the temperature. It targets those proteins and starts to unfold them, and then these proteins start to aggregate.

FLATOW: And they're - they're just - so, you destroy the proteins and the bacteria and they're gone.

Dr. JAKOB: That's at least one mechanism by which we think it works, yes, yes.

FLATOW: Hm. Does the bacteria have any way of fighting back?

Dr. JAKOB: Yeah. And this is actually what we started with. We started out with a bacterial protein called Hsp33 that we found about ten years ago, and we knew it is protecting bacteria, but we didn't know against what. And this is actually how we found bleach in the first place, because what you do when you know you have a protein and you don't know exactly what it does in bacteria, you can do something that's - a bacteria, actually, very easy to do. You remove that protein from the bacteria and then you have a bacterium that makes your protein and a bacterium that doesn't make this protein. So, otherwise, they're completely identical. And it's a very nice setup, because now, you can test under what conditions does new protein become essential for the bacteria to survive? And this is how we found - my post-doc in the lab, Jeannette Winter, the first author of the study, found it out because she treated the bacteria with bleach, and we found when the bacteria lacked the Hsp33, they were more sensitive to bleach. They also started to have more proteins aggregated, and so - and they died with much lower concentrations of bleach. In volatile bacteria, on the other hand, which express Hsp33, we had fewer protein aggregates and they withstood a higher concentration of bleach.

FLATOW: Talking about bleach this hour on Talk of the Nation: Science Friday from NPR News with Ursula Jakob. Why bleach can hurt you also? I mean, the good cells, if you are exposed to it, or even the chlorine compound of it.

Dr. JAKOB: That is true. So, what hurts us is mainly when we inhale chlorine gas; that's really what hurts us the most. And this can happen, for instance, and you might know from your mother or grandmother, never mix bleach with ammonia, for instance, because you do the chlorine gas, and that can be fairly toxic when you inhale it. What many people don't realize is that - I find that always quite fascinating - is that we actually, people, we invented bleach, because bleach has been invented or a major evolution has come up with bleach about - many, many millions of years ago. Because we have in our body these little bleach factories that are called neutrophils; they're white blood cells, and all they do is they find bacteria in our body that they want to fight, and they do that by taking these bacteria up and then releasing very high concentrations of bleach to kill all these bacteria.

FLATOW: So, our body is making bleach itself to kill the bacteria.

Dr. JAKOB: Absolutely.

FLATOW: Wow.

Dr. JAKOB: So, we actually just reinvented something evolution has come up with long, long time ago.

FLATOW: Now, we talk about inflammation earlier. Could this bleaching be causing inflammation during an attack?

Dr. JAKOB: That is something scientists are looking into, because what happens is, especially at sites of chronic inflammation, that you have neutrophils, these white blood cells, that make that bleach. And it might be this uncontrolled secretion of bleach to the - not only to the inside where the bacteria, but to the outside that starts then damaging the own proteins in the body, absolutely.

FLATOW: Wow. So, we've come full circle on the inflammation question.

Dr. JAKOB: I think so, too. Yes.

(Soundbite of laughter)

FLATOW: And I did not know that we make our own bleach.

Dr. JAKOB: There's also the idea that we also make bleach in our mucosal membranes, so in our bronchi and then in our intestine, to limit bacterial inflammations - bacterial colonization. There was a very nice study in Science a few years ago which showed in fruit flies that there is an enzyme that makes and secreted hypochlorous acid, the active ingredient of bleach, and it limits and reduces the extent of bacterial colonization in the fruit flies. And we have the same protein in our bronchi, in our gut.

FLATOW: Fascinating, Dr. Jakob.

Dr. JAKOB: Yes, yeah.

FLATOW: So, you're a bleach expert.

(Soundbite of laughter)

FLATOW: Thank you very much for taking time to talk with us.

Dr. JAKOB: Thank you. It was a pleasure. Thank you.

FLATOW: And good luck to you. Ursula Jakob is an associate professor associate professor in the Department of Molecular, Cellular and Developmental biology at the University of Michigan in Ann Arbor. Everything you wanted to know about bleach-produced inside your body.

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