Isolation and molecular recognition of heavy metal and antibiotic resistant bacteria in the inlet and outlet sewage of Ahvaz refinery, Iran

The influent of toxic heavy metals into aquatic environments has greatly increased and is considered a serious hazard for living organisms. In recent years, several technologies have been developed with the aim of reducing or removing heavy metals from the contaminated environment. Among these, technology developed based on microorganisms is more advantageous than other methods. In the present study, metal resistant bacteria (MRB) and antibiotic resistant bacteria (ARB) were first isolated from the sewage treatment plant of Ahvaz, Iran. Sampling was carried out from sewage. Then, 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 the agar diffusion method on lead (Pb) and cadmium (Cd) in a PHG II medium. The isolates were molecularly identified by genome sequencing. Next, the antibiotic resistant pattern of the potent metal resistant isolates (MIC > 1 mg/mL) was determined. Results showed that 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 found to be 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 enterica serovar typhi were 4.0 and 4.5 mg/mL, respectively. The isolated Bacillus cereus also showed high resistance to cefixime and penicillin.