Lupo Agnese, Ruppen Corinne, Hemphill Andrew, Spellerberg Barbara, Sendi Parham
Institute for Infectious Diseases, University of Bern, Bern, Switzerland.
Institute of Parasitology, University of Bern, Bern, Switzerland.
Int J Med Microbiol. 2014 Jul;304(5-6):717-24. doi: 10.1016/j.ijmm.2014.05.003. Epub 2014 May 16.
Group B Streptococcus (GBS) causes invasive infections in neonates, older adults and patients with comorbidities. β-hemolysin/cytolysin is an important GBS virulence factor. It is encoded by the cyl operon and confers GBS hemolytic activity. Isolates displaying hyperpigmentation are typically hyperhemolytic. Comparison of clonally identical isolates displaying different levels of pigmentation has shown transcriptional dysregulation due to mutations in components of the control of the virulence S/R (CovS/R) regulatory system. In addition, hyperpigmented isolates show decreased CAMP factor and decreased capsule thickness. In analogy to findings in group A Streptococcus, a pivotal role of CovS/R has been proposed in the host-pathogen interaction of invasive GBS infection. However, corresponding investigations on multiple clinical GBS isolates have not been performed. We prospectively collected hyperpigmented isolates found in a diagnostic laboratory and performed phenotypic, molecular and transcriptional analyses. In the period from 2008 to 2012, we found 10 isolates obtained from 10 patients. The isolates reflected both invasive pathogens and colonizers. In three cases, clonally identical but phenotypically different variants were also found. Hence, the analyses included 13 isolates. No capsular serotype was found to be significantly more frequent. Bacterial pigments were analyzed via spectrophotometry and for their hemolytic activity. Data obtained for typical absorbance spectra peaks correlated significantly with hemolytic activity. Molecular analysis of the cyl operon showed that it was conserved in all isolates. The covR sequence displayed mutations in five isolates; in one isolate, the CovR binding site to cylX was abrogated. Our results on clinical isolates support previous findings on CovR-deficient isogenic mutants, but suggest that - at least in some clinical isolates - for β-hemolysin/cytolysin and CAMP factor production, other molecular pathways may be involved.
B族链球菌（GBS）可导致新生儿、老年人及合并症患者发生侵袭性感染。β-溶血素/细胞毒素是一种重要的GBS毒力因子。它由cyl操纵子编码，赋予GBS溶血活性。表现出色素沉着过度的分离株通常具有高溶血活性。对克隆相同但色素沉着水平不同的分离株进行比较发现，由于毒力S/R（CovS/R）调控系统控制组件的突变，导致转录失调。此外，色素沉着过度的分离株显示CAMP因子减少和荚膜厚度降低。与A族链球菌的研究结果类似，CovS/R在侵袭性GBS感染的宿主-病原体相互作用中被认为起关键作用。然而，尚未对多种临床GBS分离株进行相应研究。我们前瞻性地收集了诊断实验室中发现的色素沉着过度的分离株，并进行了表型、分子和转录分析。在2008年至2012年期间，我们从10名患者中获得了10株分离株。这些分离株既包括侵袭性病原体，也包括定植菌。在3例病例中，还发现了克隆相同但表型不同的变体。因此，分析包括13株分离株。未发现某一荚膜血清型明显更常见。通过分光光度法分析细菌色素及其溶血活性。典型吸光光谱峰获得的数据与溶血活性显著相关。对cyl操纵子的分子分析表明，它在所有分离株中均保守。covR序列在5株分离株中显示有突变；在1株分离株中，CovR与cylX的结合位点被消除。我们对临床分离株的研究结果支持了先前对CovR缺陷同基因突变体的研究发现，但表明至少在一些临床分离株中，对于β-溶血素/细胞毒素和CAMP因子的产生，可能涉及其他分子途径。
