Isolation and Molecular Recognition of Heavy Metal and Antibiotic Resistant Bacteria in the Inlet and Outlet Sewage of Ahvaz Refinery, Iran

Abstract

The entrance of toxic heavy metals into aquatic environments has greatly increased, and is considered as a serious hazard for living organisms. In recent years, several technologies have been developed with the aim of heavy metals reducing or removing them from the contaminated environment. Among them, technologies which done based on the use of microorganisms have been more considered than other methods. In the present study, metal resistant bactria (MRB) and antibiotic resistant bacteria (ARB) were isolated from sewage treatment plant of Ahvaz, Iran. Sampling was carried out from the influent and effluent sewage. The parameters of the biological oxygen demand (BOD), chemical oxygen demand (COD), pH and concentration of heavy metals were detected in the samples by ICP-AES. Metal resistant bacteria were isolated by agar diffusion method on lead (Pb) and cadmium (Cd) in PHG II medium. The isolates were molecularly identified by genome sequencing. Antibiotic resistant pattern of the potent metal resistant isolates (MIC > 1 mg/mL) was determined. Pb and Cd concentrations in the sewage samples were above global standards (0.3 and 0.04 mg/mL, respectively). Bacillus cereus and Salmonella enterica subsp. enterica serovar typhi were the most potent Pb resistant isolates (MIC = 5.5 mg/mL, MBC = 6 mg/mL on both isolates). The MIC and MBC on Bacillus cereus were 3.0 and 3.5 mg/mL, and the MIC and MBC on Salmonella enteric serovar typhi were 4.0 and 4.5 mg/mL, respectively. The isolated Bacillus cereus also represented high resistance to cefixime and penicillin.