Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: Caroline on 08/09/2011 16:01:08
-
Caroline asked the Naked Scientists:
Hi,
There's the statement that _insert absolutely anything (including water)_ kills 99% of bacteria. Is this true? Can I simply wipe down a tidy bench with water before preparing food?
If this is true does the water need to be above a certain temperature, or is hotter only better for melting grease away when doing the dishes?
Kind regards,
Caroline Greville
What do you think?
-
No, in fact bacteria like/need water.
-
It sounds like the method one often uses to wash one's hands in a public restroom!!! [xx(]
I'm sure this is all semantics. If you wash a table with a warm wet washcloth, it may in fact pick up 99% of bacteria that would be in dirt, or in larger chunks of stuff.
The 1% left behind may be another species, and and might be tightly bound to the surface. A soap might help break loose the majority of that remaining bacteria.
Warm/hot water may kill some bacteria, but there will be many that are moderately heat tolerant, especially at temperatures below freezing. It will help cut grease, and in general make cleaning easier.
-
The question asked was for wiping - mechanical removal - not kill. Sure it's possible but, where it could be accomplished, it would probably not be clinically significant. A surface fouled with material including high bacterial count (think feces) can be wiped to remove sufficient material to remove 99%. But if the initial count was in the billions - you'd still have million left.
Killing of 99.9% meets the success criteria that allows "sanitizer" claim and even greater kill levels must be demonstrated to claim disinfectancy.
-
I think the one percent left behind would be well chuffed as they now have water and less competition. [;D]
-
If you rinse the surface clean with fresh water, then let it dry there will be very few bugs left.
-
Any ref's for that? Rinsing with water, with or without subsequet drying, is unlikely to effectively remove bacteria. If microbes were present, they're unlikely associated with the surface by a water soluble mechanism and tap water itself usually includes significant bacterial populations - esp. pseudomads. Drying of islated cells of pseudomnads does substnatially redcue viability but those found in water are usualy assoioated with bioflim that protects against the effect of drying.
-
aerobic or anarobic?
-
Any ref's for that? Rinsing with water, with or without subsequet drying, is unlikely to effectively remove bacteria. If microbes were present, they're unlikely associated with the surface by a water soluble mechanism and tap water itself usually includes significant bacterial populations - esp. pseudomads. Drying of islated cells of pseudomnads does substnatially redcue viability but those found in water are usualy assoioated with bioflim that protects against the effect of drying.
At the risk of being crass, it's a statement of the obvious.
Most faecal matter is composed of bacteria.
Each time I flush the toilet I demonstrate that lots of water will remove the vast majority of the bacteria present.
-
Not crass - just sophomoric.
The question involved wiping away bacteria from a surface - not removing suspended solids from a fluid-filled vessel by removing the fluid. Bacteria on surfaces don't sit on top waiting to be rinsed away. They exist in a matrix - fecal smear, biofilm, dried food or bodily fluid resdue, etc. Even tap water typically includes significant levels of pseudomonads not as isolated cells but in biofilm remnants sloughed off the water system. In wet biofilm as well as in dried films on the surface, these microbes are not simply rinsed away.
The EPA-specified methods for disinfectant registration, including those for us in toilets, require that inoculum be dried in a film of bovine serum albumin before challenge unless the surface is chemically/mechanically cleaned beforehand - rinsing with water is not recognized as cleaning.
-
You can't actually wipe something with a liquid- you use a cloth or something.
http://en.wikipedia.org/wiki/Wipe
If that wiping action removes the biofilm (and it would be expected to) then it will remove the bugs, even if the cloth is damp with plain water. Obviously, it doesn't sterilise things, but it will reduce the bacterial count.
Even flushing or rinsing will give some reduction.
Also you seem not to have noticed what I wrote "If you rinse the surface clean..."
Obviously, if you rinse it but don't get it clean then the outcome will be different. Odd as it may seem, that's why I made that stipulation.
Re."rinsing with water is not recognized as cleaning."
http://en.wikipedia.org/wiki/Washing
says "Washing is one way of cleaning,"
and
http://en.wikipedia.org/wiki/Rinse
says "
Rinse may refer to:
Washing
Mouthwash..."
so, when you say "rinsing with water is not recognized as cleaning." it seems that either you are talking about a specific application (such as the EPA's methods for testing disinfectants), or you are wrong.
-
absolutely anything (including water)_ kills 99% of bacteria.
I'm not sure about the "absolutely anything" part, although as mentioned, there is the mechanical cleansing that isn't mentioned.
Bacteria can colonize some pretty extreme environments. However, there are some environments that most bacteria have troubles growing in. For example, they have trouble growing in very concentrated sugar. So, you might as well wash your counters with your favorite pancake syrup.
Likewise, if you had 100% pure H2O water, then bacteria would have troubles growing in it. Even if you inoculated it with a bacteria culture. In fact, depending on the concentration of bacteria, many of the bacteria would eventually die. The remaining bacteria would survive only through cannibalism.
-
I always thought you need soap to kill 99% of the bacteria. Well that's according to the commercial anyway.