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Name: TJ
Status: Other
Grade:  Other
Location: SC
Country: United States
Date: August 2008


Question:
Are bacteria able to develop resistance against any disinfectant when they are periodically subjected to mild concentrations of that disinfectant?



Replies:
Yes. At low concentrations, mutations which confer resistance will begin to be selected in the population and eventually you will develop a resistant population due to natural selection. This is why the FDA requires rotation of disinfectants in pharmaceutical manufacturing facilities.

Ron Baker, Ph.D.


In order to provide an answer to this question it is important to ensure that you have an understanding of what it means for a bacteria to "develop resistance"

First of all - no single bacteria develops resistance. They do not learn to cope, or become stronger, or anything else. In fact bacteria are almost incapable of making any change during their life.

Like people, not all bacteria are exactly the same. Small changes can occur, which make the offspring not identical to the parents. These changes occur naturally as a result of incorrect duplication of genetic material, but can be accellerated if there is high levels of radiation, or other mutagenic material nearby ( mutagenic literally means causing changes ) Some of those changes may be helpful - others may not. A bacteria which cannot live in milk will not last long and poses no threat to the dairy industry, but a bacteria which is not affected by disinfectant has a great advantage.

If we take a random population of bacteria and apply a weak disinfectant solution, we will kill most of the bacteria. Those which are most able to withstand the disinfectant are the ones which will survive, and they will then multiply and pass on the ability to withstand disinfectant to many of their offspring. If we continue to apply weak disinfectant, we will again wipe out those less able to withstand, and will therefore increase the percentage of the population who are resistant. This is a classic case of Darwinian Selection at work - only the fittest will survive to breed.

So, to answer your question - if the disinfectant you are using is not 100% fatal to all bacteria even at low concentrations, then yes - bacteria can develop resistance, because those that are not killed are able to pass on their resistance to the future population.

Nigel Skelton


The ability to resist an antibiotic or disinfectant requires a genetic change. This is called a mutation. Mutations are random and usually bad for an organism. They also usually take a long time to show up but bacteria have a very short life cycle so mutations have a chance to happen more often. Just because you expose them doesn't necessarily mean they will definitely develop resistance. The right mutation also has to happen. You could go on forever and the bacteria could stay sensitive or it could develop the mutation the first time it is exposed.

Kvh



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