Investigating the role of the uncharacterized gene ygfB in the resistance of multidrug resistant Pseudomonas aeruginosa to β-lactam antibiotics

β-内酰胺酶AmpC的过度产生是β-内酰胺类抗生素耐药的重要原因 铜绿假单胞菌（Pa.）虽然已知Pa ampC表达依赖于转录激活因子AmpR，但使AmpC超生产的信号仍然难以捉摸。更好地了解这些因素可以帮助开发新的治疗策略，对多药耐药Pa菌株，这是越来越普遍的卫生保健settings.AmpC的过度生产是最常见的基因dacB和ampD，编码青霉素结合蛋白PBP 4和肽聚糖回收酰胺酶AmpD，分别失活。作为PBP 4失活的结果导致β-内酰胺抗性的关键事件似乎是（i）脱水-MurNac-五肽的高产量，其有效地去抑制AmpR，和（ii）双组分系统CreBC的活化。CreBC的激活如何导致β-内酰胺耐药性尚不清楚。在最近的一项研究中，我们鉴定了在AmpC超产Pa临床分离株ID 40中对β-内酰胺耐药性贡献最大的基因，该菌株携带dacB功能缺失突变。我们发现对完全β-内酰胺抗性至关重要的基因之一是未表征的基因ygfB。初步研究表明，YgfB在转录上抑制编码ID 40中酰胺酶AmpDh 3的ampD蛋白。缺失ygfB上调ampDh 3表达，这反过来导致ampC表达降低。这些数据表明ampDh 3的转录抑制对于确保dacB突变体中的高AmpC水平是至关重要的。在拟议的研究中，我们希望详细阐明YgfB如何有助于Pa的抗生素耐药性。

The hyperproduction of the ß-lactamase AmpC is an important cause of resistance to ß-lactams in Pseudomonas aeruginosa (Pa). While Pa ampC expression is known to depend on the transcriptional activator AmpR, the signals that enable AmpC hyperproduction remain elusive. A better understanding of such factors could help develop novel therapeutic strategies against multidrug resistant Pa strains, which are becoming increasingly prevalent in health care settings.AmpC hyperproduction is most frequently caused by inactivation of the genes dacB and ampD, which encode for the penicillin-binding protein PBP4 and the peptidoglycan-recycling amidase AmpD, respectively. The key events leading to ß-lactam resistance as a result of PBP4 inactivation seem to be (i) a high production of anhydro-MurNac-pentapeptides, which effectively derepress AmpR, and (ii) the activation of the two component system CreBC. How activation of CreBC contributes to ß-lactam resistance is unclear.In a recent study we identified the genes that contribute the most to ß-lactam resistance in the AmpC hyper-producing Pa clinical isolate ID40, a strain which carries a loss of function mutation in dacB. One of the genes we found to be crucial for full ß-lactam resistance is the uncharacterized gene ygfB. Preliminary studies suggest that YgfB transcriptionally represses the ampD paralogue encoding for the amidase AmpDh3 in ID40. Deletion of ygfB upregulates ampDh3 expression, which, in turn, leads to decreased ampC expression. These data suggest that the transcriptional repression of ampDh3 is critical to ensure high AmpC levels in a dacB mutant. In the proposed study, we want to elucidate in detail how YgfB contributes to antibiotic resistance in Pa.