Novel β-Lactamases in the Clinical Isolates of Enterobacter spp. and Klebsiella pneumoniae in Ramadi General Hospital : A Pharmacodynamics Study


Background: Enterobacter spp. and Klebsiella pneumoniae are among the most common gram-negative pathogens associated with hospital infections, they have a distinctive ability to develop antimicrobial resistance during therapy due largely to their unusual β-lactamases, AmpC and ESBLs. Aim of Study: To investigate the occurrence of novel β-lactamases (AmpC and ESBLs) in clinical isolates of Enterobacter spp. and K pneumoniae based on Pharmacodynamics approaches.Materials and Methods: A total of 165 samples collected from AL-Ramadi General Hospital represented by 15 burn swabs, 95 wound swabs and 55 urine samples from in and outpatients from October 2003 to April 2004, by API 20 E system and motility test 13 isolates have been identified to be Enterobacter spp. and 33 isolates to be K pneumoniae from a total 150 isolates in addition to four isolates of Enterobacter spp. identified from 10 isolates taken from a previous study on Klebsiella spp. The susceptibility of the isolates to β-lactam antibiotics were determined by the standard disk diffusion method as described in the guidelines of the National Committee for Clinical Laboratory standards (NCCLs). Appropriate tests were performed for detecting AmpC β-lactamase, confirming this detection, inducibility of AmpC β-lactamase, and ESBL production.Results: The interpretive reading of the antibiogram for Enterobacter spp. 1. Classical AmpC inducible enzyme: 2/17(11.8%) 2. ESBLs enzyme: 10/17(58.8%) 2. The number of derepressed or partially derepressed mutants were 7/17 (41.2%) that representing 7/14 (50%) of E. cloacae. While, for K pneumoniae infers the following: Classical low SHV-1 β-lactamase 2/33 (6.1%), All Enterobacter spp. isolates were resistant to cefoxitin but 15/17 were positive in the AmpC β-lactamase inhibition and the 3DM tests. Out of the 33 isolates of K pneumoniae one isolate was resistant to cefoxitin and showed positive result in the AmpC β-lactamase inhibition and the 3DM tests. Seven isolates of Enterobacter spp. showed blunting effect in the zone diameter of used β-lactams by cefoxitin or imipenem. According to the double disk synergy test for detecting the ESBLs enzyme, 8/17 (27.1%) of our Enterobacter isolates and 19/33 (57.6%) of K pneumoniae positive in giving phantom phenomenon. Conclusion: It is concluded that the high occurrence of the novel β-lactamases in the clinical isolates of Enterobacter spp. and K pneumoniae infers a poor control of the use of antibiotics and infection in this hospital. Key words: Enterobacter spp, Klebsiella pneumoniae, AmpC, ESBLs