The prevalence of extended spectrum beta-lactamases in acinetobacter baumannii isolates from burn wounds in Iran

Acinetobacter baumannii is a Gram-negative bacillus found in many hospital environments and its very high resistance to antimicrobial renders it as a successful nosocomial pathogen. There are many reports of Multi Drug Resistant A. baumannii from hospitals all over the world. ESBLs are beta-lactamases that hydrolyze extended-spectrum cephalosporins with an oxyimino side chain; These cephalosporins include cefotaxime, ceftriaxone, and ceftazidime. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. This study aimed to assess the incidence of ESBLs in 48 burn isolates of A. baumannii. The susceptibilities of isolates to different antibiotics were tested by the Kirby-Bauer method. The Minimum inhibitory concentration of cefotaxime for each isolate was determined by Hicomb strips in the range of 0.001-240 μg of antibiotic. For phenotypic detection of the ESBLs double disc diffusion method. Cefazolin (100%), ciprofloxacin (100%) ofloxacin (95.8%) and kanamycin (95.8%) showed the highest rate of resistance and amikacin (52%) and imipenem (14.6%) demonstrated the lowest. 45.8% of isolates showed resistance to the 11 tested antimicrobials. 46 isolates (95.8%) were resistant to all tested concentrations of Cefotaxime (The Minimum inhibitory concentrations were above 240 μg). only one isolate (2%) has been considered as ESBL producing isolate. The high resistance of isolates to cefotaxime, ceftazidime and cefepime in companion with the low number of ESBL producing isolates, proposed another resistance mechanisms for these isolates to extended-spectrum cephalosporins.