Heat resistant bacteria?
January 29, 2010 1:44 AM   Subscribe

Will heat treating food lead to heat-resistant bacteria?

Over prescription of antibiotics has led to antibiotic-resistant bacteria. There are bacteria at the bottom of the sea that live next to incredibly hot hydrothermal vents.

Is it possible that the heat treatment factories use to kill a lot of the bacteria in packaged foods could lead to bacteria becoming heat resistant?
posted by devnull to Science & Nature (7 answers total) 1 user marked this as a favorite
Yes they could, but there are a couple of reasons why it is not common.

First, most antibiotics target a single gene or pathway. To get resistance, all you need to do is alter that pathway or gene, or make a pump that takes the antibiotic out of the cell. This is usually one or a couple of genes, so a small mutational distance away, or can easily be spread on plasmids or phage. In contrast, high temperature requires every single pathway in the bacteria to adapt, as none of them are likely to function at higher temperatures. You cant just pump out the heat, you need to change your metabolism, your DNA replication, your cell wall etc. There are heaps of mutations of small effect: it is easier to get a couple and tolerate a few more degrees but to survive higher temperatures would require sustained selection, which does not often happen.

Think pasteurisation, where milk is heated to 72C to reduce the number of bacteria. There is no reinoculation here. Even if bacteria survive the heat treatment through a heritable means, their next step is into your gut, not back into the cow. It is unlikely that the descendants will ever get back into a cow, to redo the cycle and gain more heat resistance. In contrast, any pathogenic bacteria that survive antibiotics will likely cause another infection, and be reexposed to antibiotics, leading to more selection for resistance.

Lastly, adapting to one environment eg high heat, often leads to lower fitness in another environment eg host body temperature especially when the environments are multigenic, like heat stress. If you can tolerate heat, you will likely be a lousy pathogen.
posted by scodger at 2:01 AM on January 29, 2010 [22 favorites]

Note, also, that if a company were to find bacteria growing in their packaged food, then it would be promptly destroyed. And there is no special collection of genes that will protect an organism from the disposal methods employed then.
posted by kisch mokusch at 2:10 AM on January 29, 2010

Could I piggyback on this question and Scodger's excellent answer to ask: What about alcohol and/or bleach?
posted by Mike1024 at 4:22 AM on January 29, 2010

Previously re: resistance to alcohol. My favourite line, "like expecting humans to develop a resistance to fire."
posted by anaelith at 4:28 AM on January 29, 2010 [1 favorite]

I'm not a biologist, but I have a feeling that that's like asking if heat-treating humans could lead to heat-resistant humans.

Yeah, over time I'm sure that the human race could evolve to a SLIGHTLY higher range of temperature, but there's still a certain point at which humans would still fry up no matter what. I would say the same is true for bacteria (save for the bacterium species who are already adapted to super-heated temperatures, but those strains usually aren't stable in temperatures WE find comfortable anyway, so we wouldn't encounter them to begin with).
posted by EmpressCallipygos at 4:52 AM on January 29, 2010

The issue is the mode of killing. An antibiotic is typically a single compound with a very specific mode of action. A small change to a single protein might be sufficient to confer resistance to an antibiotic - something analogous to immunity to HIV in humans as a result of a mutation to the gene responsible for the cell receptor CCR5.

Heat isn't targeted. It's like having a load of entropy delivered by a dump truck. Hundreds and hundreds of changes would likely be required. Eventually you might get a bacteria that is heat resistant, but it might very well no longer be interested in your Kraft Lunchables, now preferring a diet of hydrogen sulfide and strontium.
posted by Kid Charlemagne at 5:18 AM on January 29, 2010

There are two factors involved here when it comes to resistance to heat, bleach, and alcohol. First, like Kid Charlemagne pointed out, evolving resistance to these would require lots (as in thousands) of mutations occurring in order for the bacteria to even function. Heat unfolds proteins permanently (think of what happens to an egg white, which is mainly protein, when you heat it); alcohol dissolves all lipids in the bacteria; bleach chemically attacks pretty much every organic molecule. So all of the affected proteins would have to mutate. It gets even worse -- due to mutations relying on each other, most of these mutations would have to occur simultaneously. If a protein needs two cystine amino acids to bond to each other to make the protein stronger, then just getting a mutation with one cystine isn't going to help.

Next, the vast, vast, vast majority of the time evolution to do well in one environment leads to doing less well in another, as scodger pointed out. Lots of bacteria can survive at higher temperatures because they evolved to that environment over lots of time; these bacteria can't grow / grow very slowly at room temperature. Growing slowly is not a good thing when it comes to bacteria infections, as the immune system would quickly react to the foreign bacteria. For example, the deadly strains of E. coli divide every 20-30 minutes. This is lightning fast when it comes to most bacteria, most of which divide every 6 hours - 1 week.

There are ways to evolve resistance to strong chemicals like alcohol and bleach (but not heat). If the bacteria never comes into contact with chemical, then it's safe and it doesn't have to worry about evolving all of its proteins at once. Many bacteria form biofilms, which are basically layers of slimy gunk (exceptionally organized, non-haphazard slimy gunk) which coats the whole bacteria community. An example would be plaque in your mouth -- and think about how strong it is that a dentist has to scrape it off with a hook. If a hostile chemical hits the biofilm, the slime layer might prevent the chemical from ever hitting the bacteria. This is why hospitals worry about biofilms growing on any medical equipment that stays inside of the body, like catheters.

Heat penetrates to all parts of the community, so biofilms wouldn't help with it.

I evolved bacteria communities which had resistance to dilute bleach fairly easily over the course of a few weeks (as part of graduate work). It's not super hard to do, and my lab believes this just has to do with the community increasing the layers of slime in the biofilm.
posted by Peter Petridish at 9:41 AM on January 29, 2010 [3 favorites]

« Older writing that's direct, morally complex, and...   |   Czech Wild Swans? Newer »
This thread is closed to new comments.