Alm Richard A, Johnstone Michele R, Lahiri Sushmita D
Infection Innovative Medicines Unit, AstraZeneca R&D Boston, Waltham, MA, USA
Infection Innovative Medicines Unit, AstraZeneca R&D Boston, Waltham, MA, USA.
J Antimicrob Chemother. 2015 May;70(5):1420-8. doi: 10.1093/jac/dku568. Epub 2015 Jan 28.
The spread of NDM-1 amongst Enterobacteriaceae has highlighted a significant threat to the clinical management of serious infections. The combination of aztreonam and avibactam, a non-β-lactam β-lactamase inhibitor, may provide a much-needed therapeutic alternative. This combination was potent against most NDM-containing Enterobacteriaceae, although activity was diminished against many Escherichia coli isolates. These E. coli isolates were characterized to elucidate the mechanism of decreased susceptibility to aztreonam/avibactam.
MIC determinations were performed using broth microdilution, and whole-genome sequencing was performed to enable sequence-based analyses.
The decreased susceptibility was not due to avibactam being unable to inhibit the serine β-lactamases found in the E. coli isolates. Rather, it was manifested by a four-amino-acid insertion in PBP3. This same insertion was also found in non-NDM-containing E. coli that had reduced susceptibility to aztreonam/avibactam. Construction of an isogenic mutant confirmed that this insertion resulted in decreased susceptibility to aztreonam and several cephalosporins, but had no impact on carbapenem potency. Structural analysis suggests that this insertion will impact the accessibility of the β-lactam drugs to the transpeptidase pocket of PBP3.
The acquisition of β-lactamases is the predominant mechanism of β-lactam resistance in Enterobacteriaceae. We have demonstrated that small PBP3 changes will affect the susceptibility to a broad range of β-lactams. These changes were identified in multiple MLST lineages of E. coli, and were enriched in NDM-containing isolates. However, they were not present in other key species of Enterobacteriaceae despite significant conservation among the PBP3 proteins.
NDM-1在肠杆菌科细菌中的传播凸显了其对严重感染临床治疗的重大威胁。氨曲南与非β-内酰胺类β-内酰胺酶抑制剂阿维巴坦联合使用，可能提供一种急需的治疗选择。这种联合用药对大多数携带NDM的肠杆菌科细菌具有强效，不过对许多大肠杆菌分离株的活性有所降低。对这些大肠杆菌分离株进行特征分析，以阐明其对氨曲南/阿维巴坦敏感性降低的机制。
采用肉汤微量稀释法进行最低抑菌浓度（MIC）测定，并进行全基因组测序以进行基于序列的分析。
敏感性降低并非由于阿维巴坦无法抑制大肠杆菌分离株中发现的丝氨酸β-内酰胺酶。相反，其表现为PBP3中出现四个氨基酸的插入。在对氨曲南/阿维巴坦敏感性降低的非NDM携带的大肠杆菌中也发现了相同的插入。构建同基因突变体证实，这种插入导致对氨曲南和几种头孢菌素的敏感性降低，但对碳青霉烯类药物的效力没有影响。结构分析表明，这种插入将影响β-内酰胺类药物进入PBP3转肽酶口袋的可及性。
获得β-内酰胺酶是肠杆菌科细菌对β-内酰胺类耐药的主要机制。我们已经证明，PBP3的微小变化会影响对多种β-内酰胺类药物的敏感性。这些变化在大肠杆菌的多个多位点序列分型（MLST）谱系中被发现，并且在携带NDM的分离株中富集。然而，尽管PBP3蛋白之间存在显著保守性，但在肠杆菌科的其他关键菌种中并未出现这些变化。
