Production of plasmid-mediated ß-lactamases in Pseudomonas aeruginosa isolated from burn patients

Pseudomonas aeruginosa is the most important pathogen causing nosocomial infections in burn patients. The existence of ß-lactamase producing isolates exhibiting resistance to most ß-lactam antimicrobial agents greatly complicates the clinical management of patients infected with such isolates. The aim of this study was to evaluate plasmid mediated ß-lactamase production in Pseudomonas aeruginosa isolates. 80 isolatedPseudomonas aeruginosa were isolated from patients with nosocomial infections admitted to Motahari Burn Center in Tehran from March 2004 to February 2005. ß-lactamase production was determined by Iodomertric test, and plasmids were extracted by alkaline lyses method. Electroporation was used for transfection of E. coli DH5α with extracted plasmids. ß-lactamase production was positive in all Pseudomonas aeruginosa isolates. Most of the strains (97.5%) showed between one and three plasmid bands in agarose gel. Only large plasmids were transferred to E. coli DH5α by electroporation, and ß-lactamase production was positive in all of transformed E. coli DH5α. The results indicate that the ß-lactamase producing Pseudomonas aeruginosa isolates are predominant in the Motahari Burn Center, and the plasmids commonly involve in ß-lactamase production. Therefore, these plasmids may transfer resistance to the same or different species.