A Low-Affinity Penicillin-Binding Protein 2x Variant Is Required for Heteroresistance in Streptococcus pneumoniae
A Low-Affinity Penicillin-Binding Protein 2x Variant Is Required for Heteroresistance in Streptococcus pneumoniae
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DOI：
10.1128/aac.02547-14
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发表时间：
2014-07-01
影响因子：
4.9
通讯作者：
Hilty, Markus
中科院分区：
文献类型：
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作者：
Engel, Hansjuerg;Mika, Moana;Hilty, Markus
肺炎链球菌对青霉素的异抗性是指亚群在比 MIC 预期更高的抗生素浓度下生长的能力。这可能使得传统的耐药性测试不可靠并导致治疗失败。我们研究了主要 β-内酰胺耐药决定簇青霉素结合蛋白 2b (PBP2b) 和 PBP2x 以及次要耐药决定簇 PBP1a 在青霉素异质耐药中的作用。通过群体分析谱(PAP)测试在非异抗性菌株R6背景中含有来自异抗性菌株Spain(2349)(23F)的PBP基因的转化体的异抗性。我们发现 pbp2x，而不是单独的 pbp2b 或 pbp1a，赋予 R6 异质抗性。然而，没有观察到 pbp2x 表达的变化，因此，表达与耐药亚群比例的增加无关。此外，通过 PAP 对 ciaR 破坏突变体评估了 CiaRH 系统介导不依赖于 PBP 的 β-内酰胺耐药性的影响，但未发现异种耐药表型。我们还表明，含有低亲和力 pbp2x 的转化子的高抗性亚群（HOM 星）在青霉素平板上选择后会出现抗性增加，在无选择培养基上传代后部分恢复。鸟枪法蛋白质组学分析显示，在这些高度耐药的亚群中，由 pstS、phoU、pstB 和 pstC 编码的磷酸盐 ABC 转运蛋白亚基蛋白上调。总之，低亲和力 pbp2x 的存在使得某些肺炎球菌菌落能够在 β-内酰胺存在下存活。磷酸盐 ABC 转运蛋白基因的上调可能代表对抗生素应激的可逆适应。
Heteroresistance to penicillin in Streptococcus pneumoniae is the ability of subpopulations to grow at a higher antibiotic concentration than expected from the MIC. This may render conventional resistance testing unreliable and lead to therapeutic failure. We investigated the role of the primary beta-lactam resistance determinants, penicillin-binding protein 2b (PBP2b) and PBP2x, and the secondary resistance determinant PBP1a in heteroresistance to penicillin. Transformants containing PBP genes from the heteroresistant strain Spain(2349)(23F) in the nonheteroresistant strain R6 background were tested for heteroresistance by population analysis profiling (PAP). We found that pbp2x, but not pbp2b or pbp1a alone, conferred heteroresistance to R6. However, a change of pbp2x expression was not observed, and therefore, expression does not correlate with an increased proportion of resistant subpopulations. In addition, the influence of the CiaRH system, mediating PBP-independent beta-lactam resistance, was assessed by PAP on ciaR disruption mutants but revealed no heteroresistant phenotype. We also showed that the highly resistant subpopulations (HOM star) of transformants containing low-affinity pbp2x undergo an increase in resistance upon selection on penicillin plates that partially reverts after passaging on selection-free medium. Shotgun proteomic analysis showed an up-regulation of phosphate ABC transporter subunit proteins encoded by pstS, phoU, pstB, and pstC in these highly resistant subpopulations. In conclusion, the presence of low-affinity pbp2x enables certain pneumococcal colonies to survive in the presence of beta-lactams. Upregulation of phosphate ABC transporter genes may represent a reversible adaptation to antibiotic stress.