In this study, we report the insertion sequence ISPpu21 in the oprD porin gene of carbapenem-resistant Pseudomonas aeruginosa isolates from burn patients in Tehran, Iran. Antibiotic susceptibility tests for P. aeruginosa isolates were determined. Production of metallo-β-lactamases (MBLs) and carbapenemase was evaluated and the β-lactamase-encoding and aminoglycoside-modifying enzyme genes were investigated by PCR and sequencing methods. The mRNA transcription level of oprD and mex efflux pump genes were evaluated by real-time PCR. The outer membrane protein profile was determined by SDS–PAGE. The genetic relationship between the P. aeruginosa isolates was assessed by random amplified polymorphic DNA PCR. In all, 10.52% (10/95) of clinical isolates of P. aeruginosa harboured the ISPpu21 insertion element in the oprD gene. The extended-spectrum β-lactamase-encoding gene in ISPpu21-carrying isolates was blaTEM. PCR assays targeting MBL and carbapenemase-encoding genes were also negative in all ten isolates. The rmtA, aadA, aadB and armA genes were positive in all ISPpu21 harbouring isolates. The relative expression levels of the mexX, mexB, mexT and mexD genes in ten isolates ranged from 0.1- to 1.4-fold, 1.1- to 3.68-fold, 0.3- to 8.22-fold and 1.7- to 35.17-fold, respectively. The relative expression levels of the oprD in ten isolates ranged from 0.57- to 35.01-fold, which was much higher than those in the control strain P. aeruginosa PAO1. Evaluation of the outer membrane protein by SDS–PAGE suggested that oprD was produced at very low levels by all isolates. Using random amplified polymorphic DNA PCR genotyping, eight of the ten isolates containing ISPpu21 were shown to be clonally related. The present study describes a novel molecular mechanism, ISPpu21 insertion of the oprD gene, associated with carbapenem resistance in clinical P. aeruginosa isolates.

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Background and Objectives. The aim of this study was to determine the frequency of bla NDM, bla PER, bla VEB, bla IMP, and bla VIM type genes among A. baumannii isolates from hospitalized patients in two hospitals in Tehran, Iran. Patients and Methods. Antibiotic susceptibility tests were performed by Kirby-Bauer disc diffusion and Broth microdilution methods. The frequency of MBL (metallo-beta-lactamase) and ESBL (extended-spectrum-beta-lactamase) producers was evaluated by CDDT. The β -lactamases genes were detected by PCR and sequencing methods. Results. The resistance of A. baumannii isolates against tested antibiotics was as follows: 103 (95.4%) to ceftazidime, 108 (100%) to cefotaxime, 105 (95.7%) to cefepime, 99 (91.7%) to imipenem, 99 (91.7%) to meropenem, 87 (80.6%) to amikacin, 105 (97.2%) to piperacillin, 100 (92.6%) to ciprofloxacin, 103 (95.4%) to piperacillin/tazobactam, 44 (40.7%) to gentamicin, 106 (98.1%) to ampicillin/sulbactam, 106 (98.1%) to co-trimoxazole, 87 (80.6%) to tetracycline, and 1 (1.8%) to colistin. Using combined disk diffusion test, 91 (84.2%) and 86 (86.86%) were ESBL and MBL producers, respectively. The prevalence of bla PER-1, bla VEB-1, bla IMP-1, and bla VIM-1 genes was 71 (78.03%), 36 (39.5%), 3 (3.48%), and 15 (17.44%), respectively. Conclusions. The prevalence of ESBLs and MBLs-producing A. baumannii strains detected in this study is a major concern and highlights the need of infection control measures.

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Background: Pseudomonas aeruginosa and Acinetobacter baumannii are the common causes of nosocomial infections especially among patients with burn injuries. Objectives: The current study aimed to determine the frequency of blaIMP, blaVIM, blaDIM, blaAIM, blaGIM and blaNDM genes among P. aeruginosa and A. baumannii strains isolated from patients with burn injuries hospitalized in Shahid Motahari hospital, Tehran, Iran. Methods:The current cross-sectional study evaluated a total of 309 nonduplicate isolates of P. aeruginosa and 189 isolates of A. baumannii collected from different clinical samples of patients with burn injuries in Shahid Motahari hospital in Tehran, Iran, from 2012 to 2015. Antibiotic susceptibility tests were conducted by Kirby-Bauer disc diffusion and broth microdilution methods according to the clinical and laboratory standards institute (CLSI) guidelines. The frequency of metallo-beta-lactamase (MBL) producers was evaluated by the combination disk diffusion test (CDDT). The blaIMP, blaVIM, blaDIM, blaAIM, blaGIM and blaNDM genes were detected by polymerase chain reaction (PCR) and sequencing techniques. Results: The most effective agent against the studied isolates was colistin. By CDDT, it was found that among 278 imipenem resistant P. aeruginosa strains, 178(64.02%) were MBL producers. The blaIMP-1 and blaVIM-1 genes were detected in 30(16.8%) and 52(29.2%) of P. aeruginosa isolates, respectively. Result of 187 imipenem resistance A. baumannii strains showed that 85(45.4%) were MBL producers. The blaOXA-51, blaIMP-1 and blaVIM-1 genes were detected in 187(100%), 10(5.3%) and 34(18.18%) of A. baumannii isolates, respectively. Conclusions: The high prevalence of MBLs-producing P. aeruginosa and A. baumannii strains in the study were one of the major concerns.