The effects of exposure to heavy metals under laboratory conditions were studied in the bacteria AB6 and AB4 isolated from a polluted site. 16S rRNA sequencing divulged that the AB6 and AB4 were phylogenetically related to Enterobacter cloacae and Bacillus subtilis. The examined biological responses includes concentration of protein, the activity of Catalase (CAT), superoxide dismutase (SOD), glutathione peroxidise (GR) and the level of lipid peroxidation. The strains were treated with different concentrations of copper, lead, cadmium and chromium based on the minimum inhibitory concentrations. No significant differences were observed for lipid peroxidation levels between control and treated strains exposed to 75, 20, 5 and 20mg/L Cu, Pb, Cd and Cr (E.cloacae) and 75, 5, 4 and 15mg/L Cu, Pb, Cd and Cr respectively (B.subtilis), implies that both isolates have potential to tolerate increased ROS generation produced by heavy metals. However, increased concentration of metal ions results in increased lipid peroxidation levels which affirmed that the isolates were under stress. Protein content and the activity of CAT, SOD and GR were found to be increased when bacteria exposed to low concentrations of metal ions whereas increased metal ion concentrations results in decreased protein content and antioxidant enzymes. This study clearly reveals that the defensive nature and the adaptive mechanism of E. cloacae and B. subtilis against free radical induced toxicity.