Marshall Isabel, Henkel Maggy, Balogh Halie, Stempel Robin, Monge E Renee, Valenzano Gabriel Z, Blackledge Meghan S, Miller Heather B
Department of Biology, High Point University, High Point, North Carolina.
Department of Chemistry, High Point University, High Point, North Carolina.
bioRxiv. 2025 Jun 5:2025.06.05.657702. doi: 10.1101/2025.06.05.657702.
Methicillin-resistant (MRSA) is a bacterial pathogen that relies on expression of a wide range of virulence factors. Hemolysins are a diverse collection of cytolytic toxins that promote virulence by being excreted and lysing host blood cells. We previously reported on novel anti-virulence compounds that modulate hemolysis in vitro, including a brominated carbazole (compound 8) and the active ingredient in Claritin (loratadine). We analyzed expression and activity of MRSA hemolysins in two hospital-acquired strains. Even with the same staphylococcal cassette chromosome (SCC) type, the strains displayed unique responses to loratadine where both repression and elevation of hemolysis occurred. We hypothesized that modulation of hemolysis by these putative Stk1 inhibitors would extend to community-acquired strains of MRSA. Furthermore, we wanted to determine if Stk1 was the only hemolysis regulatory protein being engaged by these compounds. To test this, we examined compound 8 and loratadine's effects on two different USA300 strains, in addition to deletion mutants for a range of hemolysis regulatory genes. We observed strain-specific regulation of hemolysis by Stk1. Loratadine continued to downregulate both alpha and beta hemolytic activity in USA300 JE2 in both Stk1-dependent and independent pathways. Finally, we report that this anti-virulence compound effectively disrupts hemolysis by modulating global regulators at the mRNA level including the and systems that likely contribute to reduced hemolysin levels. Both and mRNA reductions extended to a human cell line model of MRSA infection. Together, these results expand our knowledge of loratadine's function as a virulence modulator.
Methicillin-resistant (MRSA) is a human pathogen of concern worldwide. It can cause infections of the skin, soft tissue, blood, and lungs, among others, in both community and hospital settings. This work evaluates loratadine, the active ingredient in Claritin, as an anti-virulence compound. We show that loratadine is effective at lowering expression of hemolysin genes in MRSA and, concomitantly, lessening host blood cell hemolysis due to staphylococcal hemolysin proteins. This effect occurs in the presence and absence of loratadine' proposed target, a serine-threonine kinase called Stk1. In a model of human infection, every hemolysin gene expression is also downregulated by loratadine. This FDA-approved antihistamine has many properties that warrant repurposing as an anti-virulence therapy.
耐甲氧西林金黄色葡萄球菌（MRSA）是一种依赖多种毒力因子表达的细菌病原体。溶血素是一类多样的细胞溶解毒素，通过分泌并裂解宿主血细胞来促进毒力。我们之前报道了新型抗毒力化合物，它们在体外可调节溶血作用，包括一种溴化咔唑（化合物8）和开瑞坦中的活性成分氯雷他定。我们分析了两种医院获得性菌株中MRSA溶血素的表达和活性。即使具有相同的葡萄球菌盒式染色体（SCC）类型，这些菌株对氯雷他定也表现出独特的反应，溶血作用既有抑制也有增强。我们推测这些假定的Stk1抑制剂对溶血作用的调节会扩展到社区获得性MRSA菌株。此外，我们想确定Stk1是否是这些化合物作用的唯一溶血调节蛋白。为了验证这一点，我们除了检测一系列溶血调节基因的缺失突变体之外，还研究了化合物8和氯雷他定对两种不同的USA300菌株的影响。我们观察到Stk1对溶血作用具有菌株特异性调节。氯雷他定在USA300 JE2中通过依赖Stk1和不依赖Stk1的途径持续下调α和β溶血活性。最后，我们报道这种抗毒力化合物通过在mRNA水平调节全局调节因子有效地破坏溶血作用，这些全局调节因子包括可能导致溶血素水平降低的 和 系统。 和 mRNA的减少在MRSA感染的人类细胞系模型中也有体现。总之，这些结果扩展了我们对氯雷他定作为毒力调节剂功能的认识。
耐甲氧西林金黄色葡萄球菌（MRSA）是一种全球关注的人类病原体。它可在社区和医院环境中引起皮肤、软组织、血液和肺部等部位的感染。这项研究评估了开瑞坦中的活性成分氯雷他定作为一种抗毒力化合物的作用。我们表明氯雷他定能有效降低MRSA中溶血素基因的表达，并相应减少因葡萄球菌溶血素蛋白导致的宿主血细胞溶血。无论是否存在氯雷他定假定的靶点——一种名为Stk1的丝氨酸 - 苏氨酸激酶，这种作用都会发生。在人类感染模型中，氯雷他定也会下调每个溶血素基因的表达。这种经美国食品药品监督管理局（FDA）批准的抗组胺药具有许多特性，值得重新用作抗毒力疗法。
