IMPACT OF DIFFERENT ENVIRONMENTAL PARAMETERS UPON THE SUSCEPTIBILITY TO HEAVY METALS SALTS IN ESCHERICHIA COLI AQUATIC STRAINS

Purpose: to investigate the relationships among the expression of susceptibility to heavy metal salts, different incubation temperatures and chemical composition of the culture media in E. coli aquatic strains. 100 strains of E. coli isolated from Black Sea were investigated for the expression of resistance to different bivalent metals (Cu, Co, Mn, Zn, Ni) compounds. The experiments were performed comparatively at different incubation temperatures (22°C, 37°C and 44°C) in aerobic and anaerobic conditions, NaCl concentrations (from 0 to 10%), glucose (1.5 and 3%) and pH (5.0, 7.2 and 9.6). The metals susceptibility patterns varied with the tested parameter and the bivalent metal compounds. The temperature growth induced an increase in susceptibility of the tested strains to Zn (from 85% at 22°C, 20% at 37°C and 100% at 44°C), Mn (from 50% at 22°C, 15% at 37°C and 75% at 44°C), Cu (from 10% at 22°C, 0% at 37°C and 55% at 44°C), Co (from 10% at 22°C, 0% at 37°C and 30% at 44°C), Ni (from 0% at 22°C, 0% at 37°C and 5% at 44°C). Concerning the influence of salinity, the highest 10% NaCl induced to occurrence of susceptibility to all tested metals, followed by 2, 6 and 7% NaCl with susceptibility to 4 of 5 metals. The highest susceptibility levels to Zn and Mn was expressed in inverse order to 3, 4, 6, 7, 0, 2 and 0.5 % NaCl, while to Cu at 3, 2 and 7% NaCl. The tested strains were very resistant to Ni and Co, at the majority of tested salinities. Concerning the relationship between the chemical composition of the culture medium and the susceptibility levels to metals, the higher glucose concentration of 3% and the alkaline pH induced higher rates of susceptibility Mn, Zn and Ni. In conclusion the expression of heavy metals susceptibility features of the E. coli strains is strongly influenced by the incubation temperature and salinity, demonstrating the role of these parameters in the selection of resistance genes in the aquatic strains.