Determination of Minimum Inhibitory Concentration of Potassium Tellurite Against Escherichia Coli Isolates from Human Urinary Tract and from Normal Faecal Flora

Obective:Resistance to heavy metal ions has been reported in many bacteria. Since any change in the bacterial activity can have important consequnesc both from scientific and clinical aspects, this study was performed for the determination of potassium tellurite resistance in the clinical isolates of Escherichia coli. Subjects and The minimum inhibitory concentration (MIC) of potassium tellurite was determined for 449 isolates of Escherichia coli, isolated from infected urinary tract or normal fecal flora, using standard agar dilution method. Approximatley half (48.7%) of the isolates had MIC of ≤1µg/ml after 24 hours of incubation at 35 ºC. Many of the bacteria that were cultured with low concentrations of potassium tellurite, ≤ 5 µg/ml, overcame the toxicity of this heavy metal when they were re-incubated for the additional 24 hours. The MIC for these isolates was increased, so that the difference between the MIC after 24 and 48 hours of incubation became significant (P ≤ 0.001). In medium containing ≥10 μg/ml of potassium tellurite, the bacteria formed typical black colonies. No statistically significant difference was found between the MIC of bacteria that where isolated from urinary tract infection or normal fecal flora.Since resistance to heavy metals can be simultaneous with resistance to antibacterial agents, determination of simultaneous resistance to antibacterial agents and other heavy metals in this bacterium and other bacterial genus is necessary in this region.