Wolter Daniel J, Black Jennifer A, Lister Philip D, Hanson Nancy D
Center for Research in Anti-Infectives and Biotechnology, Creighton University School of Medicine, Omaha, NE 68178, USA.
J Antimicrob Chemother. 2009 Aug;64(2):294-300. doi: 10.1093/jac/dkp185. Epub 2009 May 25.
Although Pseudomonas aeruginosa from cystic fibrosis patients are well known for their antibiotic resistance, isolates that are highly susceptible to multiple drug classes have also been encountered. In this study, hypersusceptible P. aeruginosa isolates were analysed for changes in intrinsic resistance mechanisms to explain the observed phenotype.
P. aeruginosa strains PA30 and PA431 were isolated from the sputa of cystic fibrosis patients and susceptibilities were determined by agar dilution. Isolates were genetically unrelated by PFGE analysis. Expression of efflux pumps, porins, a chromosomal cephalosporinase and a gene, glmS, previously implicated in hypersusceptibility were evaluated by real-time RT-PCR, outer membrane protein analysis and beta-lactamase hydrolysis assays.
PA30 was hypersusceptible to beta-lactams, fluoroquinolones and antimetabolites, with MICs at least 4-fold lower than those for the prototype strain PAO1, while PA431 was hypersusceptible to beta-lactams and antimetabolites. Both isolates overproduced the porin OprF but showed down-regulation in the production of the carbapenem channel OprD despite carbapenem hypersusceptibility. PA30 had decreased expression of the mexAB-oprM pump involved with intrinsic antibiotic resistance but overexpressed the mexCD-oprJ and mexEF-oprN efflux systems normally associated with acquired resistance. PA431 showed down-regulation of oprM, the last gene in the mexAB-oprM operon, but overexpressed the mexXY pump. The ampC beta-lactamase was weakly inducible in strain PA30, corresponding to cefoxitin hypersusceptibility.
The changes in expression of several intrinsic mechanisms in the hypersusceptible strains did not correlate with the observed phenotype. These data highlight the complex interactions of resistance mechanisms in P. aeruginosa and their roles in drug susceptibility.
尽管囊性纤维化患者的铜绿假单胞菌以其抗生素耐药性而闻名，但也遇到了对多种药物类别高度敏感的分离株。在本研究中，对超敏感的铜绿假单胞菌分离株的固有耐药机制变化进行了分析，以解释观察到的表型。
从囊性纤维化患者的痰液中分离出铜绿假单胞菌菌株PA30和PA431，并通过琼脂稀释法测定其敏感性。通过PFGE分析确定分离株在基因上不相关。通过实时RT-PCR、外膜蛋白分析和β-内酰胺酶水解试验评估外排泵、孔蛋白、染色体头孢菌素酶和先前与超敏感性有关的glmS基因的表达。
PA30对β-内酰胺类、氟喹诺酮类和抗代谢物高度敏感，其MIC至少比原型菌株PAO1低4倍，而PA431对β-内酰胺类和抗代谢物高度敏感。两种分离株均过量产生孔蛋白OprF，但尽管对碳青霉烯类药物超敏感，但碳青霉烯通道OprD的产生却下调。PA30与固有抗生素耐药性相关的mexAB-oprM泵的表达降低，但超表达通常与获得性耐药性相关的mexCD-oprJ和mexEF-oprN外排系统。PA431显示mexAB-oprM操纵子中的最后一个基因oprM下调，但mexXY泵超表达。PA30菌株中的AmpCβ-内酰胺酶诱导较弱，这与头孢西丁超敏感性相对应。
超敏感菌株中几种固有机制的表达变化与观察到的表型不相关。这些数据突出了铜绿假单胞菌耐药机制的复杂相互作用及其在药物敏感性中的作用。
