Document Type: Brief Report
Department Of Microbiology, Kerman University of Medical Sciences, Kerman, I.R. Iran.
In this study the mechanism of chromium (Cr) and copper (Cu) resistance in Pseudomonas aeruginosa was
investigated. For this reason, 50 isolates of this microorganism were separated from 345 burn patients hospitalized in burn unit of Kerman hospital, Iran, during May 2001 to April 2002. Susceptibility/resistance of the isolates to KCrO4, CuSO4, 5 H2O, AgNO3 and HgCl2 was determined by the agar dilution method. Among
them, 6% were highly resistant to KCrO4 (MIC 50 mM), 56% were resistant to CuSO4, 5 H2O (MIC 10 mM),
while, all the isolates were sensitive to HgCl2 and AgNO3 with MIC range 0.5 -1 mM, respectively. Metal
resistant isolates exhibited different rate of Cr and Cu accumulation. Isolates 14, 39 and 50 accumulated
11,14 and 15 mM/g biomass chromate, similarly, isolate 24 accumulated 8 mM/g biomass copper. The
accumulation of Cr and Cu was mainly surface bound (biosorption), since considerable quantity of these
heavy metals was lost from the cell biomass after treating the cells with 50 mM EDTA. Furthermore, P. aeruginosa isolates did not produce H2S. X-ray diffraction analysis of the cell surface exposed to the above
heavy metal ions revealed that Cr and Cu were mainly deposited on the cell surface in the form of chromium
and copper sulfide (CrS and CuS). These complexes were in the form of electron dense nanoparticles ranging
in size from 10 to 40 nm in diameter. However, cells treated with EDTA did not show such complexes.