Adams-Sapper Sheila, Nolen Shantell, Donzelli Grace Fox, Lal Mallika, Chen Kunihiko, Justo da Silva Livia Helena, Moreira Beatriz M, Riley Lee W
School of Public Health, Division of Infectious Diseases and Vaccinology, University of California, Berkeley, Berkeley, California, USA.
Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
Antimicrob Agents Chemother. 2015;59(6):3281-9. doi: 10.1128/AAC.05100-14. Epub 2015 Mar 23.
Enterobacteriaceae strains producing the Klebsiella pneumoniae carbapenemase (KPC) have disseminated worldwide, causing an urgent threat to public health. KPC-producing strains often exhibit low-level carbapenem resistance, which may be missed by automated clinical detection systems. In this study, eight Klebsiella pneumoniae strains with heterogeneous resistance to imipenem were used to elucidate the factors leading from imipenem susceptibility to high-level resistance as defined by clinical laboratory testing standards. Time-kill analysis with an inoculum as low as 3 × 10(6) CFU/ml and concentrations of imipenem 8- and 16-fold higher than the MIC resulted in the initial killing of 99.9% of the population. However, full recovery of the population occurred by 20 h of incubation in the same drug concentrations. Population profiles showed that recovery was mediated by a heteroresistant subpopulation at a frequency of 2 × 10(-7) to 3 × 10(-6). Samples selected 2 h after exposure to imipenem were as susceptible as the unexposed parental strain and produced the major outer membrane porin OmpK36. However, between 4 to 8 h after exposure, OmpK36 became absent, and the imipenem MIC increased at least 32-fold. Individual colonies isolated from cultures after 20 h of exposure revealed both susceptible and resistant subpopulations. Once induced, however, the high-level imipenem resistance was maintained, and OmpK36 remained unexpressed even without continued carbapenem exposure. This study demonstrates the essential coordination between blaKPC and ompK36 expression mediating high-level imipenem resistance from a population of bacteria that initially exhibits a carbapenem-susceptibility phenotype.
产肺炎克雷伯菌碳青霉烯酶（KPC）的肠杆菌科菌株已在全球范围内传播，对公众健康构成了紧迫威胁。产KPC菌株通常表现出低水平的碳青霉烯耐药性，这可能会被自动化临床检测系统漏检。在本研究中，使用了8株对亚胺培南具有异质性耐药的肺炎克雷伯菌菌株，以阐明根据临床实验室检测标准，导致从亚胺培南敏感转变为高水平耐药的因素。用低至3×10⁶CFU/ml的接种量以及比最低抑菌浓度（MIC）高8倍和16倍的亚胺培南浓度进行时间杀菌分析，结果导致最初99.9%的菌被杀灭。然而，在相同药物浓度下孵育20小时后，菌量完全恢复。群体分析表明，恢复是由频率为2×10⁻⁷至3×10⁻⁶的异质性耐药亚群介导的。暴露于亚胺培南2小时后选取的样本与未暴露的亲本菌株一样敏感，并产生主要的外膜孔蛋白OmpK36。然而，在暴露后4至8小时之间，OmpK36消失，亚胺培南的MIC至少增加32倍。从暴露20小时后的培养物中分离出的单个菌落显示出敏感和耐药亚群。然而，一旦诱导产生，高水平的亚胺培南耐药性得以维持，即使没有持续的碳青霉烯暴露，OmpK36也仍然不表达。本研究证明了blaKPC与ompK36表达之间的基本协同作用，介导了从最初表现出碳青霉烯敏感表型的细菌群体中产生高水平的亚胺培南耐药性。
