Kills 99.9% of bacteria

1. Jan 4, 2006

dleacock

"Kills 99.9% of bacteria"

You know how on basically all anti-bactiera product commericals (soap, kictchen cleaner, hand santizer..etc), they always say "kills 99.9% of bacteria", what I'm wondering is, what is that 0.1% that they cant kill, is it something specific?

hope this doesnt sound like to silly of a question

2. Jan 4, 2006

shruth

Bacteria, due to a variety of reasons, have the ability to develop resistance to most anti-bacterial agents. So if a large enough sample of bacteria are taken, there will be a very very tiny fraction which are resistant. So when they say 99.9% of bacteria, they are acknowledging this fact.

Though different bacterial strains have varying capacities to develop resistance, I do not know of any specific strains which are resistant to disinfectants in general. Maybe a bacteriologist might offer her/his opinion.

3. Jan 4, 2006

dleacock

ok, heh... cause what i'm picturing is this strain of bacertia thats immune to it, and its that %0.1

I find bacteria to be really interesting, I found this used biology textbook on amazing. looking forward to that comming in

4. Jan 4, 2006

iansmith

Staff Emeritus
There is two to consider when you try to sanitize or sterilize a surface or any other thing: Time and the number of bacteria present. Resistance has nothing to do with it most of the time.

Here how it works. In the product there is specific concentration of the anti-bacterial agent inside. So when you spread the product, there is a limited amount of chemical that can interact with a specific number of bacteria at a time. So the larger the number of bacteria the larger the amount of product must be applied. Also, time is another factor. The product take a certain amount of time to interact with its target and takes a certain amount of time to kill the target.

So when they test their product, they used it as described in their direction. So they set a specfic number a bacteria on a surface and then treat the surface. They then recover the bacteria from the surface and count them. the lower the number the more efficient the killing by the product. So at 99.9% your product can handle about 1000 bacteria per mL or cm3. The more the 9 the better.

Also you have to take into account that science does not work with absolute certainties. Although we recover a given amount of bacteria only part of that recovered material is looked at and there might be mistake. Therefore there is no way for people to know for sure that 100% of the bacteria have been killed.

Last edited: Jan 4, 2006
5. Jan 4, 2006

shruth

No....I am pretty positive that it is not any one particular bacterial strain. But species like Staphylococcus have a very high resistance development rate.
Bacteria are interesting....because they have had millions of years to evolve more than we have had

Last edited: Jan 4, 2006
6. Jan 4, 2006

dleacock

makes sense, thanks for the response.

I also read that bacteria have the ability to pass their genetics onto other bacteria that isnt of their decent, it was called "hortizontal..." something. is this true?

7. Jan 5, 2006

iansmith

Staff Emeritus
Yes it true. It is called Horizontal gene transfer (HGT). There is different ways a bacteria can pick up DNA from another bacteria.

There something called conjugation. This is dependent on a cell to cell contact.
http://www.hhmi.org/biointeractive/animations/conjugation/conj_frames.htm

Some bacteria can also pick up DNA from the environment. The best examples are Streptococcus pneumoniae and Haemophilus influenzae.

Also viruses may transfer bacterial genetic material into a new recipent.

8. Jan 5, 2006

scott1

It might be a legel thing if it says it killes 100% of bacteria the FDA or somthing might do some testing and then they find some of the bacteria doesn't get killed they might make them do a recall or somthing.If it says 99.9% it whould adovid them form going to court.

9. Jan 5, 2006

DaveC426913

This, by the way, is why anti-bacterial soaps are a bad idea. They wipe out perfectly good, harmless bacteria and leave behind resistant types as well as lots of rich feeding ground for other types to thrive.

Anti-bacterial soaps are actually going to be the cause of widespread bacterial infections.

Same logic goes for antibiotics.

Did we learn nothing from Wells' Martians?

10. Jan 5, 2006

matthyaouw

I've actually been meaning to ask about that for a while, so thanks for the pre-empive answer!

One question though- In order to prevent the spread of MRSA and other resistant strains, some hospital wards have alcohol based handwash despensers at the entrance to each ward, and won't allow you to enter until you've cleaned your hands. Are these a good idea or not?

11. Jan 5, 2006

iansmith

Staff Emeritus
The problem is not the use of anti-bacterial soaps but the misuses of it.

I don't think the general public should have acces to anti-bacterial soap. Most people do not know how to use soap and wash their hand properly.

Efficient anti-bacterial soaps and antibiotics that are used properly are very powerfull tool. Resistance is harder to acquire when these are use properly.

Washing your hand is always the best idea to prevent disease.

The mode of action of alcohol against bacteria is different then most antibacterial agent. It is very hard for resistance to develop against alcohol even when misused. These solution should have 70-75% alcohol content. This concentration is the most best for killing. The only problem alcohol does not kill spores, some viruse and fungus but luckly Staph aureus does not produce spores.

12. Jan 5, 2006

DaveC426913

Agreed. It should be used in circumstances where cleanliness is particularly important. Note that these clean conditions are temporary. Once that situation (such as surgery or other hospital things) is resolved, one goes back to normal bacteria presence. That way, one never gets vulnerable.

This is true. And note that normal washing cleans mostly due to mechanical removal, so no issues about resistance - and it works on all types of critters, including spores etc. It also removes the oils and dirt that these critters thrive on.

As for alcohol stations and hospital clean conditions, don't get my wife started on that. She worked front-line during the SARS scare here in Toronto. Wacky. Great gaping holes in protocol.

13. Jan 5, 2006

dleacock

how does normal soap then do the trick of killing bacteria?

If I'm understand the issue correctly, the problem with antibacterial soap is that it kills both good and bad bacteria, right?

Well how does regular soap then work? Does it just take off dirt and grime which the bacteria would live off?

14. Jan 5, 2006

DaveC426913

Well, it also mechanically removes the bacteria. That, as I understand it, is the preferred way.

15. Jan 5, 2006

Mk

Where can I get a hand washing guide?

Is that evaporating hand soap antibacterial than? I think it's 60-65% usually.

16. Jan 5, 2006

Staff Emeritus
My daughter, who knows something about these issues, says the surfactants in soap, designed to break down fatty and waxy substances, disrupt the cell walls.

She also confirmed that the 99.9% is a science thing, lab accuracy, not a government or legal thing. In fact she says the Department of Health refers to the 99.9% level of activity as "100% effectiveness".

Last edited: Jan 5, 2006
17. Jan 6, 2006

iansmith

Staff Emeritus
Both regular and antibacterial soap have a broad spectrum of activity. So both good and bad bacteria will be kill.

Any health related agency should have a hand washing protocol to be distributed to the population.