plasmid mediated metal and antibiotic resistance in pseudomonas aeruginosa strains isolated from burn patients

pseudomonas aeruginosa is a leading cause of bum infections, and antibiotic- resistant strains of this bacterium are emerging due to extensive application of antibiotics in the bum unit of hospitals. in this study 50 strains of p. aeruginosa were isolated from bum patients infected with this micro-organism in the bum unit of a general hospital in kerman, iran over one year [may 1999-aprii2000]. sensitivity/ resistance of the isolates for antibiotics and metals was determined by mic test. 46% of the isolates were resistant to ciprofioxacin, kanamycin (k), gentamicin (gm), tetracycline (te) and chloramphenicol ( c ). 35% were resistant to amikacin (an), ceftriaxone (ceft), and cefotaxime (ctx), and 10% were resistant to imipenem (imp) and piperacillin (pip). the isolates exhibited varied mic's to metal ions. 87% were sensitive to cadmium (cd), 62% to lead (pb), 91 % to mercury (hg), 54% to zinc (zn), 85% to chromium (cr), and 83% to arsenate (ars). among them, strain 16 was found to be resistant to pb, cr, and zn as well as te, c, gm, and k. conjugation and transformation experiments revealed the transfer of ter, cr, krand gmr along with pbr to a sensitive strain of p. aeruginosa ptcc1074.1 (rif) but not to e. coli k12 hb101.1(rifr). subsequent plasmid isolation and agarose gel electrophoresis (0.7%) confirmed the presence of three-plasmid bands in strain 16 and the transconjugant. furthermore, strain 16 accumulated a maximum amount of pb (50µm) within 60 min. and reached a plateau afterwards.