Study of Multi-metal Resistance in Bacteria Highly Resistant to Mercury Isolated from Effluent of Dental Clinics

Abstract

Heavy metals pollution represents an important environmental problem. One of these metals is mercury. The
aim of this research was isolating bacteria highly resistant to mercury from dental clinic effluent to investigate
their growth potential in the presence of other heavy metals, such as Zn, Cu, Ni, Ag, Cd and Pb. Three dental
wastewater samples were selected and their mercury concentrations, pH, EC, BOD5 and COD were determined.
The mercury-resistant bacteria were found to belong to the genera of Pseudomonas, Proteus, Citrobacter,
Bacillus, Corynebacterium and Staphylococcus. In examining multi-metal resistances, the pattern of hexa-R
was seen in the case of Citrobacter and Pseudomonas genera. The highest tolerated concentration of heavy
metals was 25.6 mM which is related to Ag and Cu and tolerated by Citrobacter isolate. It is also indicated that
Citrobacter was the most resistant isolates to Cd with significant difference (P < 0.05). Results of this study
demonstrate the occurrence of different groups of bacteria, capable of high tolerance to mercury with a
potential to tolerate a variety of other toxic heavy metals suggest that, resistance to many types of toxicants
may be present in the same organism; therefore, such organisms have high potential for biotechnology
purposes.