Farra Anna, Islam Sohidul, Strålfors Annelie, Sörberg Mikael, Wretlind Bengt
Division of Internal Medicine, Department of Infectious Diseases, Karolinska Institutet, Karolinska University Hospital, Solna, Stockholm, Sweden.
Int J Antimicrob Agents. 2008 May;31(5):427-33. doi: 10.1016/j.ijantimicag.2007.12.016. Epub 2008 Mar 28.
The main mechanism of imipenem resistance in Pseudomonas aeruginosa is via downregulation of the gene for OprD porin. In a previous study, it was shown that the level of resistance did not parallel with the degree of downregulation of the porin gene, thus arguing for the existence of other resistance mechanisms. Penicillin-binding protein (PBP) 2 and PBP3 are involved in carbapenem resistance in Escherichia coli. The genes for PBPs were sequenced in three imipenem-resistant clinical strains and these strains were conjugated with two susceptible P. aeruginosa PA0 strains, selecting for auxotrophic markers. In all the clinical and resistant isolates there was no obvious elevation of AmpC cephalosporinase. The active sites of PBP1b (ponB), PBP2 (pbpA), PBP3 (pbpB) and PBP6 (dacC) had no mutations in any of the examined strains. Production of oprD mRNA was significantly lower in clinical strains and transconjugants after selection for the proB marker (PA4565 at 5113kb). The clinical strains had alterations in OprD that were not found in transconjugants. Our findings suggest that PBPs do not play a role in imipenem resistance in the clinical strains examined here, but that a regulatory gene for oprD contributing to carbapenem resistance is located close to the proB gene.
铜绿假单胞菌对亚胺培南耐药的主要机制是通过下调孔蛋白OprD的基因。在先前的一项研究中，已表明耐药水平与孔蛋白基因的下调程度并不平行，因此表明存在其他耐药机制。青霉素结合蛋白（PBP）2和PBP3与大肠杆菌对碳青霉烯类的耐药性有关。对三株耐亚胺培南的临床菌株中的PBPs基因进行了测序，并将这些菌株与两株敏感的铜绿假单胞菌PA0菌株进行接合，选择营养缺陷型标记。在所有临床分离株和耐药株中，AmpC头孢菌素酶均无明显升高。在任何检测菌株中，PBP1b（ponB）、PBP2（pbpA）、PBP3（pbpB）和PBP6（dacC）的活性位点均无突变。在选择proB标记（位于5113kb处的PA4565）后，临床菌株和转接合子中oprD mRNA的产生显著降低。临床菌株中OprD存在改变，而在转接合子中未发现。我们的研究结果表明，PBPs在此处检测的临床菌株对亚胺培南的耐药性中不起作用，但对碳青霉烯类耐药性起作用的oprD调控基因位于proB基因附近。
