Will bacteria develop resistance?

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Special to The Times

Could the use of nanosilver products create another problem for medicine -- strains of bacteria that are resistant to silver? Although silver is not used to treat disease, it is used in hospital settings to speed wound-healing, prevent eye infections in newborns and as a coating for catheters, where it can cut infection rates.

Here, too, there is much surmise and not much evidence, although researchers do know there are strains of bacteria that have developed resistance to silver.

“If [nanosilver] is used without restriction, then you’re increasing the chances that a number of microbes will develop resistance to it,” says Andrew Maynard, chief science advisor for the Project on Emerging Nanotechnologies at the Woodrow Wilson International Center for Scholars.


Maynard says he worries especially about bacteria that develop resistance to the major classes of antibiotics and silver.

But Dr. David Weber, an infectious disease and public health expert at the University of North Carolina in Chapel Hill, isn’t convinced that silver resistance will prove much of a problem. Resistance to antibiotics occurs quite readily in bacteria once prolonged exposure to, say, penicillin, occurs. But there’s little reason to suppose that resistance to silver would develop so easily, he says.

An antibiotic like penicillin works by hitting a bacterium in a limited fashion, at specific sites. Because the killing is done precisely, the bacterium has a good chance of developing a mutation that would confer resistance.

In contrast, silver kills microbes in a broad, unspecific fashion -- like tossing a bomb at a bacterium. It hits many essential points such as a bacterium’s entire respiratory system. This makes it much more difficult for silver-resistance to develop.

And even if tolerance did develop, Weber says, increasing the dose of silver the bacterium is exposed to will solve the problem in most cases.