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Name: James
Status: Other
Age: 50s
Location: N/A
Country: N/A
Date: N/A 


Question:
Question is what is the minimal(threshold) type of current necessary to kill bacteria? AC or DC?, voltage?, were the microorganisms in solution of some sort, etc.

Any and all info would be helpful.



Replies:
Dear Mr. Gross,

My experience with electrical shock and bacteria is limited to the application of 'electroporation' (also called electro-transformation), a method to force DNA into bacteria. The bacteria are suspended in a solution of glycerol and glucose (isotonic so that the bacteria won't burst as they do in water, and free of ions to give sufficient resistance). This solution is put in a cuvette sided with two electrodes and DNA is added. An electrical current is applied for several milisec, and the result is that the DNA is 'shot' into the bacterial cells.

The voltage should be high enough to be effective, but not too high so that the bacteria survive. When salts (from the growth medium) are not sufficiently removed, the voltage results in a current (a flash!) and the bacteria are killed. I am not sure weather it is the heat or the current itself (or the combination) that kills the bugs. How much current is needed for electroporation, and how much the bacteria can survive, is dependent on the organism. Note, however, that these experiments are optimalized for cell survival, not for killing. I did a quick search for you on the internet about applications:

Research is going on to use electrical current to kill micro-organisms, see for instance this (lay-man) article on killing bacteria and viruses in medical blood products

(http://www.ioa.com/~dragonfly/blackbox.html).

Bacteria that form biofilms (multiple layers of tightly packed cells) on catheders are a serious problem in invasive medicine. Such bacteria are hard to treat with antibiotics because the inner layers are not reached. The application of electrical current (1-10 mA/cm2), often in combination with antibiotics is used for desinfection of such devises. See for instance this scientific publication

(http://aac.asm.org/cgi/reprint/40/9/2012?view=reprint&pmid=8878572).

Another application to kill bacteria with help of electricity is to rinse foods/cutting boards etc. with electrolyzed water

(see http://www.scienceagogo.com/news/20000728182516data_trunc_sys.shtml).

In this case it is the acidity of the water and oxidation/reduction that distroy the microorganisms.

I hope this answers your questions

Trudy Wassenaar



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