Schmidtke Amber J, Hanson Nancy D
Department of Medical Microbiology and Immunology, Center for Research in Anti-Infectives and Biotechnology, Creighton University, Omaha, Nebraska 68178, USA.
Antimicrob Agents Chemother. 2008 Nov;52(11):3922-7. doi: 10.1128/AAC.00341-08. Epub 2008 Sep 8.
AmpD indirectly regulates the production of AmpC beta-lactamase via the cell wall recycling pathway. Recent publications have demonstrated the presence of multiple ampD genes in Pseudomonas aeruginosa and Escherichia coli. In the prototype P. aeruginosa strain, PAO1, the three ampD genes (ampD, ampDh2, and ampDh3) contribute to a stepwise regulation of ampC beta-lactamase and help explain the partial versus full derepression of ampC. In the present study, the roles of the three ampD homologs in nine clinical P. aeruginosa isolates with either partial or full derepression of ampC were evaluated. In eight of nine isolates, decreased RNA expression of the ampD genes was not associated with an increase in ampC expression. Sequence analyses revealed that every derepressed isolate carried mutations in ampD, and in two fully derepressed strains, only ampD was mutated. Furthermore, every ampDh2 gene was of the wild type, and in some fully derepressed isolates, ampDh3 was also of the wild type. Mutations in ampD and ampDh3 were tested for their effect on function by using a plasmid model system, and the observed mutations resulted in nonfunctional AmpD proteins. Therefore, although the sequential deletion of the ampD homologs of P. aeruginosa can explain partial and full derepression in PAO1, the same model does not explain the overproduction of AmpC observed in these clinical isolates. Overall, the findings of the present study indicate that there is still an unknown factor(s) that contributes to ampC regulation in P. aeruginosa.
AmpD通过细胞壁循环途径间接调节AmpCβ-内酰胺酶的产生。最近的出版物表明，铜绿假单胞菌和大肠杆菌中存在多个ampD基因。在原型铜绿假单胞菌菌株PAO1中，三个ampD基因（ampD、ampDh2和ampDh3）有助于对ampCβ-内酰胺酶进行逐步调节，并有助于解释ampC的部分与完全去阻遏现象。在本研究中，评估了九个ampC部分或完全去阻遏的临床铜绿假单胞菌分离株中三个ampD同源物的作用。在九个分离株中的八个中，ampD基因的RNA表达降低与ampC表达增加无关。序列分析表明，每个去阻遏的分离株在ampD中都携带突变，在两个完全去阻遏的菌株中，只有ampD发生了突变。此外，每个ampDh2基因都是野生型，在一些完全去阻遏的分离株中，ampDh3也是野生型。通过使用质粒模型系统测试了ampD和ampDh3中的突变对功能的影响，观察到的突变导致AmpD蛋白无功能。因此，尽管铜绿假单胞菌ampD同源物的顺序缺失可以解释PAO1中的部分和完全去阻遏现象，但相同的模型无法解释在这些临床分离株中观察到的AmpC过量产生。总体而言，本研究结果表明，仍有一个未知因素有助于铜绿假单胞菌中ampC的调节。
