Characterization of the Extended-Spectrum beta-Lactamase Producers among Non-Fermenting Gram-Negative Bacteria Isolated from Burnt Patients

Background & Aims of the Study: Extended-spectrum beta-Lactamases (ESBLs) represent a major group of beta-lactamases which are responsible for resistance to oxyimino-cephalosporins and aztreonam and currently being identified in large numbers throughout the world. The objective of this study was to characterize ESBL producers among non-fermenter gram-negative bacteria isolated from burnt patients. Materials &Methods: During April to July 2012, 75 non-fermenter gram-negative bacilli were isolated from 240 bacterial cultures collected from wounds of burnt patients admitted to the Burn Unit at Shahid Motahari Hospital (Tehran, Iran). Bacterial isolation and identification was done using standard methods. Antimicrobial susceptibility testing was performed by disk diffusion method for all strains against selected antibiotics and minimum inhibitory concentration was determined by microdilution test. The ability to produce ESBL was detected through double disk synergy test among candidate strains. Results: Of 75 non-fermenter isolates, 47 Pseudomonas aeruginosa and 28 Acinetobacter baumannii were identified. The resistance of P. aeruginosa isolates to tested antibiotics in antibiogram test were 100% to cefpodoxime, 82.98% to ceftriaxone, 78.73% to imipenem, 75% to meropenem, 72.72% to gentamicin, 69.23% to ciprofloxacin and aztreonam, 67.57% to cefepime, 65.95% to ceftazidime, and 61.53% to piperacillin. The results for Acinetobacter baumannii were 100% to ceftazidime, cefepime, ciprofloxacin, imipenem, meropenem, cefpodoxime, and cefotaxim, 96.85% to gentamicin, 89.65% to ceftriaxone, 65.51% to aztreonam, and 40% to piperacillin. Double disk synergy test showed that 21 (28%) of non-fermenter isolates were ESBL producer. Conclusions: None of the third or fourth generation of cephalosporins is suitable for treatment of Pseudomonas aeruginosa and Acinetobacter baumannii isolated from burnt patients.