迄今为止,已经确定了三种碳青霉烯类耐药机制:从病原体释放的碳青霉烯酶,外膜OprD孔蛋白表达的变化,和外排泵MexAB-OprM的过表达。12株碳青霉烯酶阴性耐碳青霉烯类铜绿假单胞菌,从拉里萨大学医院住院的患者中分离出来,希腊中部,在2023年,属于各种序列类型(ST),选择并研究了它们的β-内酰胺酶的特性,关于OprD及其调节蛋白MexT的变化,以及mexR编码的MexAB-OprM调节蛋白的改变,nalC,和nalD基因。全基因组测序分析显示存在β-内酰胺酶编码基因,blaPAO存在于所有分离物中。此外,确定了恶草素酶家族的七个不同基因(blaOXA-35,blaOXA-50,blaOXA-395,blaOXA-396,blaOXA-486,blaOXA-488,blaOXA-494),每个菌株都有一到三个。关于Opro,五个菌株具有截短的结构,在环2、环3、环4和环9处,而其余菌株携带先前报道的氨基酸变化。Further,另一个菌株具有截短的MexR;然而,另外两个菌株具有完全修饰的NalC序列。MexT的活性形式,负责下调OprD生产,作为NalD蛋白的完整序列,在所有研究的菌株中都发现了。结论是截断的OprD,MexR,和NalC蛋白,在八种菌株中检测到,可能导致蛋白质失活,有助于碳青霉烯抗性。然而,四种菌株在OprD中进行了已知的修饰,MexR,还有NalC,正如先前在易感菌株和耐药菌株中报道的那样,这一发现表明铜绿假单胞菌碳青霉烯耐药性的复杂性。
To date, three carbapenem resistance mechanisms have been identified: carbapenemase released from the pathogen, changes in the expression of the outer membrane OprD porin, and overexpression of the efflux pump MexAB-OprM. Twelve carbapenemase-negative carbapenem-resistant Pseudomonas aeruginosa strains, isolated from patients hospitalized at the University Hospital of Larissa, Central Greece, during 2023, which belonged to various sequence types (STs), were selected and were studied focusing on the characterization of their β-lactamases, on changes to OprD and its regulator
MexT proteins, and on alterations to the MexAB-OprM regulator proteins encoded by the mexR, nalC, and nalD genes. Whole genome sequencing analysis revealed the presence of β-lactamase encoding genes, with blaPAO present in all isolates. Additionally, seven different genes of the oxacillinase family (blaOXA-35, blaOXA-50, blaOXA-395, blaOXA-396, blaOXA-486, blaOXA-488, blaOXA-494) were identified, with each strain harboring one to three of these. Regarding the OprD, five strains had truncated structures, at Loop 2, Loop 3, Loop 4, and Loop 9, while the remaining strains carried previously reported amino acid changes. Further, an additional strain had a truncated MexR; whereas, two other strains had totally modified NalC sequences. The active form of
MexT, responsible for the downregulation of OprD production, as the intact sequence of the NalD protein, was found in all the strains studied. It is concluded that the truncated OprD, MexR, and NalC proteins, detected in eight strains, probably led to inactive proteins, contributing to carbapenem resistance. However, four strains carried known modifications in OprD, MexR, and NalC, as previously reported in both susceptible and resistant strains, a finding that indicates the complexity of carbapenem resistance in P. aeruginosa.