Abstract

Microorganisms are known to be highly sensitive to the presence of heavy metals and some of the early attempts to control microorganisms had used copper sulphate as plant fungicide and mercury salts for some infectious diseases; but, the order of toxicity varies among different organisms and in general mercury and silver are more toxic than manganese and zinc. It has been seen that responses of organisms to heavy metal occur at concentration considerably below those at which they response to alkali and alkaline earth metal occur. Here an attempt has been made to study the susceptibility and resistance pattern of three common pathogenic bacteria, Klebsiella pneumonia, Escherichia coli and Staphylococcus aureus against heavy metals. The inhibitory effect of different concentrations of five metal salts, namely chromium, nickel, iron, cobalt and zinc on microbial growth were studied using gel diffusion method. Results show that all three study organisms were completely resistant for all concentrations of chromium and iron salts. E. coli and S. aureus were most susceptible for zinc and nickel salts as compared to K. pneumonia. In all salts, zones of inhibition were increased along with increasing concentrations of salts and maximum inhibition was seen at 150 mM concentration. All the three microbes were highly susceptible for zinc.

Key words: Chromium, iron, metal salts, resistant.