ISPpu22,a novel insertion sequence in the oprD porin gene of a carbapenem-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 blaoxa-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. © 2015,tehran university of medical science. all rights reserved.