The dispenser of anti-bacterial handsoap at my work has the ubiquitous message (of anti-bacterial soaps): “Kills 99.9% of bacteria!”
What happens to the remaining bacteria that aren’t killed, though? That is, if I wash my hands with this stuff, and kill most of the germs on my hands, won’t the rest just continue reproducing until my hands are full of them again?
(Note: I understand how soap generally works by just washing the bacteria down the drain, and that anti-bacterial soaps try to kill bacteria during the process. I’m just curious about these particular “99.9%” claims.)
I assume that the “99.9%” doesn’t necessarily mean that 0.1% of the bacteria are resistant to the antibacterial agent, but rather that 0.1% may not have been exposed to it.
But, of course, bacteria that become resistant to the antibacterial ingredient are problematic too.
I would WAG that “kills 99.9% of bacteria!” really means “when applied in significant concentrations to a laboratory agar plate containing common hand bacteria, no statistically significant evidence of living cells remained.”
Furthermore I’d imagine it’s more a legal wiggle room than anything, to account for some small proportion of more resilient strains that might survive the triclosan or 77someodd% alcohol that generally gets used in antibacterial products. Although I wouldn’t be particularly worried about those toughies infecting me, especially since you’re going to contaminate yourself as soon as you twist the faucet and very quickly end up with teeming millions…on your palms.
As a side question: does anyone know if these antibacterial soaps (e.g., ones containing Triclosan) leave behind some kind of antibacterial residue or film? IOW, do they only do their thing when you’re washing your hands, or do they provide “protection” afterwards as well?
Part of the survival is that some bacteria may be tucked in some microscopic crack where they never get exposed to whatever’s supposed to kill them. Bacteria also form biofilms (impervious layers of lots of bacteria, often including multiple species) to fortify against all sort of environmental hazards. A quick wipe down of even the strongest antibiotic will probably miss some bacteria. Guaranteed methods of killing bacteria include a good long soak in bleach, really high heat, or high-energy radiation. Fact is, you have go to pretty extaordinary lengths to kill all bacteria. Sanitation is thus more of a numbers game – try to avoid high doses of nasty pathogens, your immune system will handle the smaller doses. The vast majority of bacteria out there are pretty benign.
And, FWIW, triclosan resistance is popping up these days. From what I understand, the dose of triclosan used in ordinary antibacterial soaps isn’t enough to really be useful, but is enough to start selecting for tolerance. Most studies that I’ve heard of say the antibacterial stuff isn’t any more effective than a good scrub with ordinary soap and hot water.
I suspect it is more of a legal disclaimer than a claim of efficacy. If they claimed it “killed bacteria”, they might be open to a lawsuit by someone who inferred it killed all the bacteria, but developed an infection after using the product. By stating there could be as much as .1 percent of bacteria that survive the use of the product, it gives them a an out. Nothing is perfect, and it would be unwise to claim it was.
Quite possibly, if by “stronger” you mean “more likely to be resistant to the antibiotic”.
No. At least, doubtful.
Just to reiterate, there’s no such thing as 100% in science, especially biology. There will always be some bacteria left, somewhere, at some point, on someone.
Smeghead’s last point is key here, and in fact in Molecular Biology we rely on this fact. I can take bacteria, force them to take up DNA with an electric shock, and kill 10 million of them…but as long as ONE survives, my experiments are successful. So yes, it only takes one. And usually one survives.
The only way to definitively sterilize something would be to autoclave it, and I’m not sure that even kills 100%. Maybe hurling it into the sun would work.
Take this discussion from my food safety class as an example. Let’s say you know that treating your canned food for 1 minute at X degrees kills 90% of bacteria present. And let’s say that you that, on average, there are 1000 harmful bacteria per can. So after X minutes, you’re down to 100, then after 2X minutes, 10, and after 3X minutes, 1. What happens at 4X minutes? Obviously, you can’t have 0.1 bacteria per can. So has your food now been completely sterilized? Well, no. What you now have is, on average, one harmful bacterium in every tenth can, which is clearly a much less desirable situation. After 5X minutes, one out of every 100 cans is still potentially dangerous.
The government standard for food processing, IIRC, is that ready-to-eat food has to be processed in some way that would kill 99.9999999% of any botulism spores (the most resistant form of harmful critter) if they were present in the food to begin with. It’s either that or 99.99999% - I don’t recall for sure. Anyway, either way, that should put the “99.9%” claims of these cleaning products into perspective.
You think 99.9% is something. . . in the 1968 film “The Swimmer,” one person mentions that their water filter removes 99.99.99% (read 99 point 99 point 99) of impurities.