isppu22, a novel insertion sequence in the oprd porin gene of a carbapen- em-resistant pseudomonas aeruginosa isolate from a burn patient in tehran, iran

background and objectives: the oprd mutation and ampc overproduction are the main mechanisms of intrinsic resistance to carbapenems such as imipenem and meropenem in pseudomonas aeruginosa . materials and methods: in this study, we investigated intrinsic resistance to carbapenems including mutation of oprd and ampc overproduction in a carbapenem-resistant p. aeruginosa isolated from a burn patient by phenotypic and molecular methods. results: in our study, the carbapenem-resistant p. aeruginosa isolate was resistant to imipenem, meropenem, cefepime, gentamicin, ceftriaxone, carbenicillin, aztreonam and ciprofloxacin but was susceptible to ceftazidime and polymyxin b. the minimum inhibitory concentrations (mics) against imipenem, meropenem and ceftazidime were 64 μg/ml, 16 μg/ml and 2μg/ml, respectively. the isolate was esbls and ampc overproducer. no carbapenemase activity was detected by modified hodge test (mht). this isolate was carrying only bla oxa-10 . pcr amplification and sequencing of oprd performed on isolate resulted in pcr product of 2647bp. sequence analysis of the 2647bp product revealed insertion of a sequence of 1232 bp at position 8 in coding region of oprd. conclusion: according to the results of this study, oprd mutation and ampc overproduction can cause the main mechanism of resistance of p. aeruginosa to carbapenems.