The study of simultaneous resistance to heavy metals and antibiotics in resistant bacteria to silver and cadmium isolated from the wastewater

This laboratory study simultaneously was conducted to evaluate the resistance to heavy metals, silver, cadmium and a number of commonly used antibiotics. Sampling was done in 2014 of the two silver workshops in Isfahan, and the inlet of phase 2 of Shahin Shahr wastewater treatment plant, Isfahan. To isolate resistant bacteria to metal silver and cadmium and review multiple resistance to other metals in the medium PHG II agar with a concentration of 0.5 mM of metals and to determine the minimum inhibitory concentration (MIC) of growth, agar dilution method were used. To determine the resistance to several common antibiotics, disk diffusion techniques in agar with Kirby-Bauer method was used. In this study, molecular identification of bacteria was performed through gene sequencing 16S rDNA. New nucleotide sequences of the Cd1 and Cd2 isolates in GenBank’s database were deposited under accession numbers of KP753912 and KP753913. Most heavy metal-resistant isolated bacteria in this study had multiple resistance (MMR) compared to the Cadmium, Silver, Copper and Zinc metals and showed simultaneous resistance pattern to several heavy metals and antibiotics. Resistant isolates to cadmium compared to resistant isolates to silver had lower resistance and minimum inhibitory concentration (MIC), they also showed less resistance to a variety of antibiotics used in this study in a way that Cd2 isolate that was recognized as Dechloromonas hortensis strain MS2 was sensitive to all tested antibiotics. Since some of the isolates were highly sensitive to some of the antibiotics, the metal-resistant isolates and sensitive to antibiotic may be a proper candidates for biological removal of these metals from contaminated wastewater in the future.