铜绿假单胞菌RSCVs的致病机制与临床干预研究进展
Rugose Small Colony Variants (RSCVs) in Pseudomonas aeruginosa: Pathogenesis, Clinical Implications, and Therapeutic Advancements
DOI: 10.12677/acm.2025.1541232, PDF, HTML, XML,   
作者: 俞 清, 杜小幸*:浙江大学医学院附属邵逸夫医院肝病感染科,浙江 杭州
关键词: 铜绿假单胞菌RSCVs生物被膜c-di-GMP抗生素耐药Pseudomonas aeruginosa RSCVs Biofilm c-di-GMP Antibiotic Resistance
摘要: 铜绿假单胞菌(Pseudomonas aeruginosa)的皱缩型小菌落变异体(Rugose Small Colony Variants, RSCVs)是一种具有高生物被膜形成能力和高适应性的表型变异体,常在囊性纤维化患者的慢性感染分离株中被发现。其形成机制主要与环二鸟苷酸(c-di-GMP)信号通路的异常激活密切相关。本文系统地总结了RSCVs的分子机制、临床意义以及新型治疗策略,以期为RSCVs的基础研究与临床干预提供系统性参考。
Abstract: Rugose Small Colony Variants (RSCVs) of Pseudomonas aeruginosa are phenotypic variants with high biofilm-forming capacity and adaptability, frequently identified in chronic infection isolates from patients with cystic fibrosis. Their formation is primarily associated with the abnormal activation of the cyclic diguanylate monophosphate (c-di-GMP) signaling pathway. This review systematically summarizes the molecular mechanisms, clinical significance, and novel therapeutic strategies of RSCVs, aiming to provide a comprehensive reference for the basic research and clinical intervention of RSCVs.
文章引用:俞清, 杜小幸. 铜绿假单胞菌RSCVs的致病机制与临床干预研究进展[J]. 临床医学进展, 2025, 15(4): 2715-2722. https://doi.org/10.12677/acm.2025.1541232

1. 引言

铜绿假单胞菌(Pseudomonas aeruginosa)是医院感染的主要病原体之一,其强大的生物被膜形成能力和适应性使其在临床治疗中极具挑战性[1]。小菌落变异体(small colony variants, SCVs)最早约100年前在伤寒沙门氏菌(Salmonella enterica serovar Typhi)中发现。早期研究中,“SCV”泛指多种菌落形态较小且生长缓慢的变异体。然而,皱缩型小菌落变异体(Rugose Small Colony Variants, RSCVs)被单独定义为超强生物被膜形成的亚群,最初在铜绿假单胞菌的体外卡那霉素耐药性进化实验中被描述[2],随后逐渐被用作描述铜绿假单胞菌的超生物被膜变种的特定名称。RSCVs是一种细菌适应性变异亚群,其主要特征包括高度皱褶的菌落形态、增强的生物被膜形成能力以及对环境胁迫的高耐受性[3]。本综述从RSCVs形成的分子机制、临床意义和治疗策略三方面,全面解析RSCVs的研究进展,旨在为RSCVs的基础研究与临床干预提供全面的参考依据。

2. RSCVs的形成机制

2.1. c-di-GMP信号通路的异常激活

RSCVs的形成与第二信使环二鸟苷酸(c-di-GMP)的过度积累密切相关[2] [4]。c-di-GMP由GTP在二鸟苷酸环化酶(DGCs)催化下产生,并由磷酸二酯酶(PDEs)降解[4],通过动态平衡控制细菌在浮游状态和生物被膜状态之间转变[5]。在铜绿假单胞菌中,c-di-GMP通过促进胞外多糖和基质蛋白的合成[6],从而促使细菌生物被膜的形成。

2.1.1. Wsp信号转导通路

Wsp (Wrinkly Spreader Phenotype)是铜绿假单胞菌内源的膜应激感应通路,通过感知表面附着引发的细胞膜扰动(如蛋白错误折叠、膜完整性破坏),激活c-di-GMP信号级联以启动生物被膜形成,属于替代趋化功能信号系统的成员[7]。该系统功能异常是导致c-di-GMP升高最常见的原因,由此引发的RSCVs表型变异占比约为40%~60% [3] [8]

Wsp信号转导通路主要由六种蛋白质组成,包括膜结合的甲基受体趋化蛋白WspA、膜定位锚定蛋白WspB、信号传递辅助蛋白WspC和WspD、组氨酸激酶WspE、二鸟苷酸环化酶WspR以及磷酸酶WspF [7]。WspA感知表面相关信号后,触发磷酸化级联反应,激活WspR使其合成c-di-GMP [9],进而促进生物被膜基质的产生。

该通路中,尤其是WspF蛋白与皱缩型小菌落变异体(RSCVs)表型密切相关[10]。WspF蛋白对应的wspF基因发生框内缺失和氨基酸取代突变时,可将Wsp系统“锁定”到一种持续的活性状态,导致c-di-GMP的过量产生[11]。此外,也有研究指出WspA蛋白对应的wspA基因的框内缺失突变(如wspAΔ280-307)同样会使Wsp系统进入持续的活性状态,从而产生过量的c-di-GMP [12]

2.1.2. Yfi信号传导系统

Yfi (Yersinia filamentation inducer)信号通路是细菌(如耶尔森菌、铜绿假单胞菌)中调控环境适应和致病性的信号通路,通过感知宿主压力信号调控c-di-GMP代谢[13]。Yfi信号传导系统由三个主要组分构成:YfiN是一种膜结合的二鸟苷酸环化酶(DGCs),负责催化合成c-di-GMP;YfiR是一种周质中的抑制蛋白;而YfiB是一种外膜脂蛋白。这三者之间的相互作用调节YfiN的活性。当YfiR的抑制作用被解除时,YfiN被激活,导致c-di-GMP水平上升,进而促进皱缩型小菌落变异体(RSCVs)表型和生物被膜形成[14]

与Wsp信号转导通路类似,YfiR的突变(如转座子插入)可以解除对YfiN的抑制,使Yfi系统“锁定”在高c-di-GMP状态,从而促进生物被膜基质过度分泌[15]

2.2. Gac/Rsm调控网络的改变

Gac (Global activator of antibiotic and cyanide synthesis)系统是一个双组分信号转导系统,由组氨酸激酶GacS和反应调控蛋白GacA组成[16]。改系统通过调控下游的Rsm蛋白家族(如RsmA、RsmE)及小RNA(如RsmY、RsmZ)来影响细菌的运动性、致病性及生物被膜形成能力[17]

在铜绿假单胞菌中,RsmA通过对psl (Psl多糖合成编码基因)操纵子的翻译后修饰来调节Psl胞外多糖的产生。Psl mRNA具有广泛的5'非编码区,RsmA可以直接结合该区域并抑制psl的翻译[18]。因此RsmA蛋白功能的缺失会促进皱缩型小菌落变异体(RSCVs)表型的形成。RsmZ是铜绿假单胞菌中一个功能明确的小RNA,作为翻译阻遏物RsmA的拮抗剂,其上调导致RsmA的螯合,从而促进超生物被膜的形成[19]

2.3. 鞭毛基因突变与生物被膜增强的关联

鞭毛相关基因(如fleQflaA)的突变不仅影响细菌的运动性,还通过调控c-di-GMP和胞外多糖的水平,直接或间接促进RSCVs形成[20]。具体而言,失去鞭毛转录调控功能的fleQ突变体,通过解除对胞外多糖合成的抑制,形成超黏附生物被膜[20]。此外,flaA基因编码的鞭毛蛋白的丢失,导致鞭毛依赖的生物被膜调控反应,从而提高胞内c-di-GMP水平,促进生物被膜的形成[21]。这种鞭毛系统的功能丧失是RSCVs在宿主压力下的一种适应性进化策略,有助于细菌在复杂环境中生存和传播。

2.4. 环境压力驱动的适应性演化

在抗生素暴露、低氧或宿主免疫压力下,细菌通过高频突变(如wspFyfiR)快速进化成RSCVs以增强生存优势。例如,氨基糖苷类抗生素(如卡那霉素)通过激活PvrR-PDE途径,短暂诱导皱缩型小菌落变异体(RSCVs)表型的形成[2]。在静态培养中,氧气限制通过促进纤维素合成基因(wss)的表达,驱动铜绿假单胞菌进化出“皱褶扩散体”[22]。这些研究表明,环境压力是RSCVs形成的选择动力,揭示了生物被膜在复杂生态位中的进化优势。

2.5. 群体感应系统的调控

群体感应系统(Quorum Sensing, QS)是细菌通过分泌和感知信号分子来协调群体行为的一种机制[23]。细菌通过分泌自诱导分子(如酰基高丝氨酸内酯,AHLs;自诱导物-2,AI-2)感知种群密度,从而协调基因表达,影响生物被膜形成、毒力因子分泌等生理过程。QS系统通过调控二鸟苷酸环化酶(DGC)的活性,如WspR,上调细胞内环二鸟苷酸(c-di-GMP)水平,促进生物被膜的形成和表面黏附。当细菌感知到特定的信号分子(如AI-2、AHLs)后,会触发基因表达,调节毒力因子的分泌和生物被膜基质(如多糖、胞外DNA)的合成。

在慢性感染中,QS系统可能通过抑制急性毒素基因的表达(如RhlR调控的毒力因子),推动细菌向高生物被膜、低毒力的皱缩型小菌落变异体(RSCVs)表型进化,以逃避免疫清除[24]。这种适应性进化策略有助于细菌在宿主压力下生存和传播。

3. RSCVs的临床意义

3.1. 慢性感染中普遍存在

皱缩型小菌落变异体(RSCVs)在慢性感染中频繁被检测到。铜绿假单胞菌的RSCVs是囊性纤维化(CF)患者肺部慢性感染的主要病原菌之一。相关研究表明,在CF患者的痰液样本中,RSCVs的检出率高达30% [25]。此外,某项研究指出,在某医院重症监护病房中,患有呼吸机相关性肺炎的患者痰样本中,RSCVs的检出率达到了15.2% [26]。值得注意的是,在接受氨基糖苷类抗生素治疗的持续烧伤伤口感染患者中,也检测到了RSCVs。进一步的研究通过构建猪全层烧伤模型发现,铜绿假单胞菌在初始感染阶段经历了强烈的RSCVs阳性选择。RSCVs在感染后第3天迅速进化,并持续整个感染周期,在感染后第14天达到峰值频率,约占种群数量的2% [10]

3.2. 与不良临床结局相关

(1) 感染持续时间延长:RSCVs在压力缓解后可恢复为浮游状态,从而重新激活毒力基因,导致感染复发[3]。RSCVs形成的生物被膜对抗生素具有更高的耐受性,导致感染持续时间延长。

(2) 治疗失败率升高:RSCVs因生物被膜形成能力增强和代谢抑制,增加了机体清除的难度,显著降了低抗生素敏感性,导致治疗失败率升高[27]

3.3. 诊断挑战

(1) 表型特征干扰传统培养鉴定:RSCVs的典型特征(菌落粗糙、生长缓慢、体积小)易与污染菌(如葡萄球菌或真菌)混淆,导致漏检或误判。在囊性纤维化患者痰液培养中,RSCVs因需延长培养时间(>72小时)常被忽略[28],而常规报告仅针对快速生长的野生型菌株。此外,RSCVs在血琼脂平板上可能呈现类似凝固酶阴性葡萄球菌的干燥外观,需依赖基因型分析确认[29]

(2) 分子检测的局限性:RSCVs相关突变(如ΔwspFΔyfiR)未被纳入常规铜绿假单胞菌鉴定引物设计,导致基因型漏检。临床样本中RSCVs常包裹于藻酸盐或Pel/Psl多糖基质内,降低DNA提取效率,影响qPCR或测序灵敏度。

(3) 表型可逆性导致的假阴性:RSCVs在体外传代或脱离宿主压力后可能恢复为野生株表型,导致实验室检测时无法捕捉到原始感染状态[3]

(4) 影像学与临床症状的非特异性:RSCVs感染引发的慢性肺炎或伤口感染与普通铜绿假单胞菌感染的影像学特征重叠,且炎症标志物(如CRP、IL-6)升高模式相似,难以通过常规临床评估区分。

3.4. 传播和进化

RSCVs在慢性感染中通过基因突变和表型可逆性动态适应宿主微环境,同一感染灶内RSCVs与浮游菌共存[28],根据生存微环境变化,适应性调整群菌状态。长期抗生素暴露(如氨基糖苷类)下从野生株中筛选出RSCVs亚群,停用氨基糖苷类后,非RSCVs菌株重新占优,但RSCVs在后续重复治疗中可迅速重新占据优势,表明其具有潜伏存留和耐药记忆能力[30],从而实现适应性进化。

4. 针对RSCVs的治疗策略

4.1. 优化传统抗生素的使用方法

在抗生素对生物被膜的作用方面,氟喹诺酮类抗生素表现出最强的清除能力,而亚氨培南和头孢他啶的效果相对较弱。大环内酯类抗生素在穿透菌细胞外多糖基质方面表现最为出色,氟喹诺酮类和β内酰胺类则处于中间水平,氨基糖苷类的穿透力最弱[31]。尽管大环内酯类本身对铜绿假单胞菌的抗菌活性较弱,但其生物被膜穿透性良好,即使在亚抑菌浓度下,也能有效抑制和破坏生物被膜[32]。其中,阿奇霉素不仅能抑制藻酸盐的生成,还能干扰密度感知信号系统,从而增强细菌对过氧化氢和补体系统的敏感性[33],这使得其在抗生物被膜的临床应用中最为广泛。有研究报道硝基氧化物能够通过破坏生物被膜结构来增强环丙沙星的杀菌渗透,实现“分散–杀灭”协同效应[34]。该化合物在400 μM浓度时能够显著减少尿路致病性大肠杆菌的存活量,减少程度可达104,其效果优于单纯的环丙沙星,并且能够达到99.9%的清除阈值。在感染人膀胱细胞(T24)的模型中,该化合物也能显著降低细胞内外的尿路致病性大肠杆菌存活量,部分实现对感染的清除。然而,目前对于该化合物在铜绿假单胞菌中的治疗有效率缺乏进一步的研究。此外,在临床转化过程中,仍需解决药物渗透性、安全性和耐药性风险等诸多问题。

依据临床分离RSCVs的药敏试验结果,联合使用具有较强生物被膜清除能力的抗生素,从而实现传统抗生素治疗的优化。

4.2. 抗生物被膜策略

皱缩型小菌落变异体(RSCVs)的生物被膜主要由细胞外多糖(EPS)、细胞外DNA(eDNA)和蛋白质组分构成。研究表明,藻酸裂解酶能够破坏藻酸盐交联,减少EPS的生成[35] [36]。此外,N-乙酰半胱氨酸(NAC)可通过剂量依赖的方式剥离已形成的生物被膜。具体而言,0.5 mg/ml的NAC即可显著破坏铜绿假单胞菌成熟生物膜,且其作用呈剂量依赖性,当浓度达到10 mg/ml时,可完全清除生物膜。在0.5 mg/ml和1 mg/ml的NAC处理下,胞外多糖(EPS)产量分别降低了27.46%和44.59%。同样地,0.5 mg/ml的NAC与1/2 MIC的环丙沙星联用,可显示出协同杀菌作用,减少生物膜内的活菌数。然而,当前研究主要集中在体外实验(PAO1及20株临床菌),尚缺乏临床试验直接验证NAC对生物膜感染患者的疗效。另一方面,DNase1 L2脱氧核糖核酸酶通过降解eDNA,有效抑制铜绿假单胞菌在皮肤表面的定植以及生物被膜的构建[37]。此外,天然肉桂提取物通过抑制鞭毛蛋白合成和群体感应,减少细菌黏附及生物被膜形成[38]

4.3. 抑制细菌定植及代谢

通过改良医学材料特性以减少细菌在体内的定植,是临床常用的抑制细菌定植的手段。有研究报道,表面覆盖放射性纳米银颗粒的塑料导管能够有效抵抗多种细菌生物被膜的形成,从而显著降低留置导管引发感染并发症的风险[39]。研究发现,铜绿假单胞菌通过HecR-HecE基因开关形成功能不同的亚群,平衡生物被膜形成与分散,抑制该通路可显著减少细菌在黏膜表面的定植[40]。然而,当前研究为早期机制探索,需验证在复杂宿主环境中的效力,同时评估体内安全性和药代动力学特性。

铜绿假单胞菌的代谢及生物被膜构建依赖铁这一关键营养物质。铁含量充足时,生物被膜形成机制才会激活;铁匮乏时,生物被膜薄弱且不完整;而过高铁浓度则抑制生物被膜形成[41]。此外,通过筛选小分子库,研究鉴定出Econazole、Bithionate等化合物,可特异性阻断铜绿假单胞菌利用血红素或亚铁离子,抑制其铁依赖的定植能力[42]

4.4. 靶向c-di-GMP信号通路的新型疗法

针对c-di-GMP信号通路的治疗策略主要聚焦于抑制二鸟苷酸环化酶(DGC)以减少c-di-GMP的生成,或激活磷酸二酯酶(PDE)以加速c-di-GMP的降解。研究表明,糖基化三萜皂苷(GTS)、2'-F-c-di-GMP (c-di-GMP类似物)和三唑连接类似物等能够特异性结合二鸟苷酸环化酶[43],从而抑制其活性。此外,通过高通量筛选鉴定出的H6-335化合物,能够激活内源性磷酸二酯酶BifA的活性[44],进而调控c-di-GMP水平。还有研究报道,通过合成直接诱导c-di-GMP形成功能失活的G-四链体聚合物[45],可以阻断其信号通路,有效降低c-di-GMP浓度。在1.25 μM浓度下,该聚合物能够抑制PAO1ΔwspF (高c-di-GMP铜绿假单胞菌)生物膜形成达62.18% ± 6.76%,且对低c-di-GMP菌株(野生型PAO1)无显著影响,显示出良好的作用靶向性。然而,其仅对高c-di-GMP浓度的菌株有效,可能限制其临床适用场景,例如不适用于基础c-di-GMP水平较低的感染。此外,尽管其最佳活性浓度(1.25 μM)较低,但尚未评估体外实验与实际体内环境的复杂性,如药物的渗透性、代谢稳定性等。

5. 总结与展望

铜绿假单胞菌皱缩型小菌落变异体(RSCVs)作为高生物被膜形成能力的表型变异体,其形成机制与c-di-GMP信号通路的异常激活密切相关。Wsp和Yfi信号系统通过基因突变(如wspF缺失、yfiR失活)导致c-di-GMP过度积累,驱动胞外多糖合成及生物被膜形成。此外,Gac/Rsm调控网络失调、鞭毛基因突变以及群体感应系统(QS)的适应性调控,共同促使RSCVs在环境压力(如抗生素暴露、低氧)下进化。临床上,RSCVs与慢性感染(如囊性纤维化)高度相关,其强生物被膜特性导致抗生素耐受性升高、感染复发及治疗失败。然而,RSCVs的诊断仍面临挑战,包括表型可逆性、分子检测灵敏度不足以及与野生型菌株的临床特征重叠。

当前治疗策略聚焦于多途径干预:优化抗生素联用、降解生物被膜基质、抑制细菌铁代谢及靶向c-di-GMP通路。然而,现有疗法仍存在局限性,例如生物被膜异质性导致的耐药差异及靶向药物的临床转化难度。未来研究需进一步解析RSCVs的动态调控网络,开发基于多组学的精准诊断技术,并探索多靶点协同治疗(如纳米材料载药联合基因编辑)。此外,结合宿主–病原体互作机制及人工智能预测模型,有望为RSCVs感染的防控提供创新策略,最终改善慢性感染患者的临床预后。

NOTES

*通讯作者。

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