Constitutive high expression of chromosomal β-lactamase in Pseudomonas aeruginosa caused by a new insertion sequence (IS1669) located in ampD
Constitutive high expression of chromosomal β-lactamase in Pseudomonas aeruginosa caused by a new insertion sequence (IS1669) located in ampD
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DOI：
10.1128/aac.46.11.3406-3411.2002
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发表时间：
2002-11-01
影响因子：
4.9
通讯作者：
Hoiby, N
中科院分区：
文献类型：
--
作者：
Bagge, N;Ciofu, O;Hoiby, N
铜绿假单胞菌染色体AmpC β -内酰胺酶的表达受酰胺酶AmpD活性的负调控。在本研究中，我们检测了耐药的临床铜绿假单胞菌菌株和从体内和体外生物膜中分离的几种耐药变体，以检测ampD突变，以寻找导致染色体β -内酰胺酶高水平表达的遗传变化的证据。在两个临床分离的铜绿假单胞菌和几个生物膜分离的变体的ampD基因中发现了一个新的插入序列IS1669。IS1669在ampD中的存在导致AmpC β -内酰胺酶的高水平表达。这些菌株与参考菌株PAO1的ampD互补，导致AmpC β -内酰胺酶的表达急剧下降，头孢他啶的MIC也相应下降到与PAO1相当的水平。一种高度耐药的、组成型β -内酰胺酶产生的变异在ampD中没有突变，但在ampR中观察到一个点突变，导致Asp-135—>Asn改变。据报道，阴沟肠杆菌中AmpR的相同突变导致AmpC的表达增加450倍。然而，在许多表达高水平染色体β -内酰胺酶的分离株中，在ampD、ampR或ampD、ampR或ampC的启动子区域均未发现变化。我们的研究结果表明，可能存在多种途径导致染色体β -内酰胺酶引起的抗菌素耐药性增加。
The expression of chromosomal AmpC beta-lactamase in Pseudomonas aeruginosa is negatively regulated by the activity of an amidase, AmpD. In the present study we examined resistant clinical P. aeruginosa strains and several resistant variants isolated from in vivo and in vitro biofilms for mutations in ampD to find evidence for the genetic changes leading to high-level expression of chromosomal beta-lactamase. A new insertion sequence, IS1669, was found located in the ampD genes of two clinical P. aeruginosa isolates and several biofilm-isolated variants. The presence of IS1669 in ampD resulted in the expression of high levels of AmpC beta-lactamase. Complementation of these isolates with ampD from the reference P. aeruginosa strain PAO1 caused a dramatic decrease in the expression of AmpC beta-lactamase and a parallel decrease of the MIC of ceftazidime to a level comparable to that of PAO1. One highly resistant, constitutive beta-lactamase-producing variant contained no mutations in ampD, but a point mutation was observed in ampR, resulting in an Asp-135-->Asn change. An identical mutation of AmpR in Enterobacter cloacae has been reported to cause a 450-fold higher AmpC expression. However, in many of the isolates expressing high levels of chromosomal beta-lactamase, no changes were found in either ampD, ampR, or in the promoter region of ampD, ampR, or ampC. Our results suggest that multiple pathways may exist leading to increased antimicrobial resistance due to chromosomal beta-lactamase.