Microbes and Metals

Abstract

THE effect of metals on the growth of bacteria has been examined by Miller, Behring, and others, and another t contribution to this subject has lately been published by Dr. Meade Bolton, in the December number of the International Medical Magazine. According to Uffelmann, who smeared the surface of copper coins with liquefied jelly-cultures of cholera bacilli, the latter were destroyed in seventeen minutes; whilst on a brass coin they were alive after thirty hours, but dead after sixty hours. Bolton employed Miller's method of inoculating a tube of melted jelly with particular microbes, and pouring the contents out on a sterilised glass-plate, after which bits of the metal under examination were laid on the jelly whilst it was still soft. If the metal has an inhibitory action on the microbes, then a clear zone is left around the metal after the colonies have developed in the other parts of the jelly. The width of this zone, Dr. Bolton found, varied very considerably with different organisms, as well as with different metals. Thus carefully purified bits of silver produced in the case of cholera bacilli a clear zone 5 millimetres broad, in the case of typhoid bacilli a zone of about 1 millimetre, whilst with the closely allied colon bacillus a zone of about 5 millimetres was produced. In the case of purified gold, no inhibition was observed with the staphylococcus pyogenes aureus, colon bacillus, typhoid bacillus, or cholera bacillus. Freshly “glowed gold” had invariably no inhibitory action; and in the few cases where inhibition was observed, the gold had not been glowed for several weeks. Pure nickel, platinum wire, and platinum black aluminium, silicon, and niobium, again, also failed to give any reaction with most of the microbes examined. Throughout the investigations it was found that those metals that are resistant towards chemical reagents in general, failed to produce any effect on microbes; whilst, on the other hand, those metals which are readily attacked by chemical reagents, all exhibited a marked inhibitory action upon the growth of bacteria. This result is probably due to a solution of the metal taking place in the medium. The length of time it is necessary to leave the metals in contact with the jelly, to produce an effect on the microbes present, was tried with brass, copper, cadmium, and zinc, on the staphylococcus pyogenes aureus. The metals were put on and removed at various intervals. When cadmium was left on for a minute, there was a clear space underneath where it had rested, which extended to 1 millimetre round; when it was left on for three or four minutes, the clear space usually extended over 3 millimetres. Very similar results were obtained with zinc. With brass no effect was produced when it was left on thirty-six minutes, but after this there was more and more marked inhibition up to fifty minutes; but to produce a clear space, it was necessary to leave it on for still longer. Copper produced no visible effect under thirty-six minutes, and fifty minutes was required to produce a clear space.