【www.zhangdahai.com--村官个人工作总结】
【关键词】 金黄色葡萄球菌;异质性;耐万古霉素 近年来,耐甲氧西林金黄色葡萄球菌(methicillin-resistant Staphylococcus aureus ,MRSA)所致的医院获得性肺炎在全球范围内呈上升趋势,引起了全世界的关注。万古霉素作为治疗MRSA最常用的抗生素已经应用于临床近50年,并已成为治疗MRSA肺炎的最后一道防线。随着近年来医院获得性MRSA肺炎的增多和万古霉素的大量使用,异质性万古霉素耐药金黄色葡萄球菌(heterogeneous vancomycin-resistant staphylococcus aureus, heteroVISA)[1]和万古霉素中介耐药金黄色葡萄球菌(vancomycin-intermediate staphylococcus aureus,VISA)[2]的出现更为人们敲响了警钟。尽管目前我国未发现耐万古霉素的金黄色葡萄球菌(vancomycin-resistant staphylococcus aureus ,VRSA)[3]肺炎病例,但全国范围内heteroVISA/VISA肺炎正逐年增多,患者在足量的糖肽类抗生素治疗下死亡率仍较高,给临床治疗带来了困难和挑战。本文主要从耐药机制、治疗对策等方面对hVISA/VISA感染进行综述。�
1 定义�
万古霉素敏感性下降的金黄色葡萄球菌分为3种: 万古霉素耐药金黄色葡萄球菌(VRSA)、万古霉素中介敏感金黄色葡萄球菌(VISA)、万古霉素异质性耐药金黄色葡萄球菌(hetero-VRSA,hVRSA)。各国判断金黄色葡萄球菌万古霉素耐药折点不完全相同,美国CLSI2006 年的新标准规定MIC≥16 μg/ml为耐药,4～8 μg/ml 为中介,≤2 μg/ml为敏感。而根据英国BSAC 及瑞典SRAG 标准,MIC≥8 μg/ml即为耐药。hVRSA 是指亲代菌株对万古霉素敏感,但含有对万古霉素中介甚至完全耐药的亚克隆,出现频率为10-6或以上,可用万古霉素选择平板筛选出来,并且在无抗生素的培养基上连续培养9 d以上耐药性保持稳定[2] 。但是由于hVRSA 是在万古霉素药物平板上反复筛选出来的亚克隆,存在体外诱导的因素,并且大部分hVRSA 是通过回顾性研究发现的,其临床意义目前仍不明确。因此,美国CDC规定hVRSA 目前仅用于实验室研究,结果不作为临床报告。�
2 耐药机制�
2.1 细胞壁的改变�
2.1.1 细胞壁的增厚 细胞壁的增厚是VISA和hVRSA的一个共同特点,在临床上第一次描述VISA之前就已经有许多认识`。Hanaki等[4]研究发现VISA 和hVRSA的细胞壁较VRSA 显著增厚,且细胞壁厚度和万古霉素耐药程度相关。增厚的细胞壁主要通过“亲密诱捕”和“阻塞”现象引起万古霉素耐药,前者是指细胞壁上增多的肽聚糖单体D-丙氨酰-D-丙氨酸残基与万古霉素结合,大部分药物结合在细胞壁上,不能到达细胞质膜发挥作用;后者是指万古霉素与D-丙氨酰-D-丙氨酸残基结合,阻塞其网状结构,阻止万古霉素向细胞质膜渗透。通过电镜观察,一些菌株在未暴露于万古霉素之前并没有明显的细胞壁增厚,而在暴露万古霉素之后则有明显的细胞壁增厚[4]。�
2.1.2 肽聚糖交联减少 细胞壁谷氨酰胺非酰胺化成分增加,肽聚糖交联降低,是金葡菌对万古霉素耐药机制之一。VISA 体内6-磷酸葡糖胺合成酶活性增加,消耗大量的谷氨酰胺,未酰胺化的肽聚糖单体合成增加,后者与万古霉素结合能力增强,加强了“亲和诱捕”和“阻塞”作用。但是仅仅肽聚糖交联减少并不引起万古霉素耐药,需要和细胞壁增厚共同发挥作用[5]。�
2.1.3 青霉素结合蛋白合成改变 金葡菌有5种PBPs,其中PBP2、PBP4与万古霉素耐药相关。Moreira 等[6]发现体外诱导的VRSA 的PBP2 产量增加,并且与万古霉素MIC 增加正相关,推测可能PBP2 与万古霉素竞争结合肽聚糖前体上的靶位,阻碍万古霉素与靶位结合。PBP4 具有羧肽酶活性,可于肽聚糖上切除丙氨酸残基,避免过多的丙氨酰-丙氨酸五肽形成,保证万古霉素有效地作用于金黄色葡萄球菌。Finan 等[7]发现VISA 的PBP4含量降低,将PBP4 过度表达的高拷贝质粒导入VISA,可使万古霉素MIC降低。�
2.2 自溶性改变 自溶性下降是hVISA和VISA的一个共同特点,也是持续感染患者获得的连续菌株早期表型改变。最初日本报道的VISA菌株Mu50的自溶性是升高的[8],但是最新的数据证实,Mu50株整个细胞的自溶性也是下降的。有研究发现[9]VISA细胞壁胞壁酸可能对抑制自溶酶降解肽聚糖起一定的作用,同时还有研究表明[10]VISA自溶素之一的肽聚糖水解酶的活性改变与其自溶性下降有关。�
2.3 代谢改变Metabolic Changes
一项分析高水平耐药VISA菌株代谢的研究[11]发现其醋酸盐分解代谢障碍,进一步研究表明,在其他VISA菌株中,71%醋酸盐分解代谢也下降,而VSSA株只有8%醋酸盐分解代谢降低。作者因而得出结论:醋酸盐分解减低可导致VISA生长特征、对抗菌素的耐药性的改变和细胞间粘附的多聚糖合成增加[11]。�
2.4 染色体突变 染色体突变是金黄色葡萄球菌对万古霉素产生耐药的重要机制之一,是细菌在抗生素选择压力的不断作用下发生突变所致,该突变是一个渐进的过程。大量基因分析证实,在万古霉素暴露下,agr基因点突变引起的功能丧失有助于hVISA/VISA的选择[12],Wootton等比较了10株临床分离的VISA,11株VSSA的15个开发读码框,发现glpT和uhpT分别在G1064A和C718T处发生碱基取代,导致了终止密码子的产生,SA2468和mrphomologue分别在A814和A5917处发生碱基缺失,但这4个基因突变并不都存在于VISA中,表明耐药并不完全由基因突变引起[13]。�
3 治疗�
3.1 治疗hVISA/VISA感染的有效的抗菌药物(已上市及在研发药物) 体外试验中有许多抗菌素对hVISA/VISA有效。包括一些老药如利福平、夫西地酸和许多新药,近年来被批准用于临床的新抗菌药物有利奈唑烷(linezolid ,第1 个用于临床的�唑烷酮类药物) 、达托霉素(daptomyein ,第1 个用于临床的脂肽类药物) 、泰利霉素(tigecycline ,由克拉霉素衍生而来的酮内酯类药物) 和替加环素(静脉注射用广谱四环素类药物) 。处于临床研究阶段的新抗菌药物有头孢吡普(cef tobiprole) ,对耐甲氧西林葡萄球菌具有活性的广谱头孢菌素类药物) 、奥利万星(oritavancin) 和(dalbavancin) (均为新糖肽类药物) 。�
3.2 利福平、夫西地酸 体外试验中利福平和夫西地酸都对金黄色葡萄球菌有很好的活性,特别是对多药耐药的MRSA[14]。如单药应用很容易诱导耐药,因此应给和其他对葡萄球菌有效的药物合用。典型的联合方案有利福平联合夫西地酸或利福平联合喹诺酮类药物[15]。在澳大利亚等地区,口服利福平联合夫西地酸是治疗复杂MRSA感染的主要方案。口服利福平及夫西地酸成功的治疗一些万古霉素治疗失败的hVISA/VISA感染病例[16]。�
3.3 利奈唑胺 利奈唑胺属于新一类的完全人工合成的�唑烷酮类抗菌素,它对于万古霉素敏感性下降的金黄色葡萄球菌及凝固酶阴性的葡萄球菌仍保持敏感,MIC90保持不变[17]。尽管已经有报道利奈唑胺耐药的病例[18],但是其耐药率是很低的[19]。虽然利奈唑胺在体外是一种抑菌剂,但许多严重的MRSA、hVISA、VISA病例包括感染性心内膜炎均通过利奈唑胺治愈[17]。利奈唑胺还对一些万古霉素治疗失败的MRSA、hVISA、VISA感染病例特别有效。但对于利奈唑胺,一个重要的问题就是其毒副作用,如延长治疗是应当注意[20]。�
3.4 达托霉素 达托霉素是种环形脂肽类抗菌素。达托霉素是一种广谱抗革兰阳性菌的快速杀菌剂,为环状结构的脂肽类抗生素,通过干扰细菌胞膜对氨基酸的转运,阻碍细菌胞壁肽聚糖的合成[21],由于其作用机制较为独特,较少出现交叉耐药。但已有报道金葡菌对其敏感性下降的病例,可能与高细菌负荷的感染有关[22]。但达托霉素对hVISA/VISA仍保持杀菌活性,在一项涉及50株hVISA/VISA的研究中,通过MIC测定,hVISA/VISA对达托霉素基本上都是敏感的,其MIC范围在0.125~1 g/ml,最低杀菌浓度与最低MIC相同[23]。�
3.5 链阳菌素 奎奴普丁/ 达福普丁是原始霉素ⅠA 的衍生物和原始霉素Ⅱ B 的衍生物的混合物(3∶7),可抑制蛋白合成,对葡萄球菌、屎肠球菌效果好,对hVISA/VISA也有活性[24]。�
3.6 替加环素 替加环素是最近被FDA批准用于治疗腹腔感染和复杂性皮肤及软组织感染的一种广谱甘氨酰环素类抗菌药物,对MSSA 和MRSA均具有强抗菌活性,包括少量的VISA菌株,但是尚未广泛应用[25]。�
3.7 奥利万星Dalbavancin和达巴万星 Oritavancin正在开发的具有杀菌作用的半合成糖肽类抗菌药物奥利万星和达巴万星,抗菌谱与万古霉素基本相似,对甲氧西林敏感或耐药葡萄球菌、PRSP 和肠球菌属有效,奥利万星对耐万古霉素致病菌有效,达巴万星的作用强于万古霉素。多项研究报道了奥利万星与达巴万星的疗效和安全性。因此,上述新药有望用于MRSA、VRE,以及多药耐药肺炎链球菌的治疗[26]。达巴万星对于万古霉素及利奈唑胺耐药的hVISA/VISA仍有较好的敏感性,其MIC范围在0.06~2 μg/ml[27]。�
3.8 新型头孢菌素
新型头孢菌素类药物在体外试验及动物体内均表现出强大的抗hVISA /VISA 活性。Ceftaroline 对包括MRSA在内的金葡菌都具有强大的抗菌活性,但其对MRSA的MIC90s(2g/ml) 比 MSSA (0.25 to 0.5 g /ml)。100株hVISA/VISA菌株的MIC90 (19株VISA,81株hVISA) 也是2g/ml(0.25-4 g/ml)[28]。头孢吡普(Ceftobiprole)也对hVISA/VISA具有较好的抗菌活性[29]。�
3.9 泰利霉素 泰利霉素是一种半合成的脂糖肽类抗菌素,是万古霉素的衍生物,其对MSSA、MRSA及VISA均有良好的抗菌活性,其对VISA的抗菌活性也比较好,MICs值比较接近[30]。�
参 考 文 献�
[1] Hiramatsu K,Hanaki H, Ino T, et al. Methicillin-resistant Staphylococcus aureus clinical strain with reduced vancomycin susceptibility. J Antimicrob Chemother,1997,40: 135-146.�
[2] Hiramatsu K, Aritaka N, Hanaki H, et al. Dissemination in Japanese hospitals of strains of Staphylococcus aureus heterogeneously resistant to vancomycin.Lancet,1997,350: 1670-1673.�
[3] Centers for Disease Control and Prevention (CDC). Staphylococcus aureus Resistant to vancomycin -United States,2002. MMWR Morb Mortal Wkly Rep,2002,51: 565-567. �
[4] Cui, L., X. Ma, K. Sato, K. Okuma, F. C. Tenover, E. M. Mamizuka, C. G.Gemmell, M. N. Kim, M. C. Ploy, N. El-Solh, V. Ferraz, and K. Hiramatsu.2003. Cell wall thickening is a common feature of vancomycin resistance in Staphylococcus aureus. J. Clin. Microbiol,41:5-14.�
[5] Julian, K., K. Kosowska-Shick, C. Whitener, M. Roos, H. Labischinski, A. Rubio, L. Parent, L. Ednie, L. Koeth, T. Bogdanovich, and P. C. Appelbaum. 2007. Characterization of a daptomycin-nonsusceptible vancomycinintermediate Staphylococcus aureus strain in a patient with endocarditis.Antimicrob. Agents Chemother,51:3445-3448.�
[6] Moreira, B., S. Boyle-Vavra, B. L. deJonge, and R. S. Daum. 1997. Increased production of penicillin-binding protein 2, increased detection of other penicillin-binding proteins, and decreased coagulase activity associated with glycopeptide resistance in Staphylococcus aureus. Antimicrob.Agents Chemother,41:1788-1793.�
[7] FINAN JE, CLIMO MW, ARCHER GL.2000. Role of Penicillin Binding Protein 4 (PBP4) in Vancomycin Susceptibility among Clinical Vancomycin Intermediate Susceptible Staphylococcus aureus (VISA) Isolates. Intersci Conf Antimicrob Agents Chemother,2000,40: 75.�
[8] Utaida, S., R. F. Pfeltz, R. K. Jayaswal, and B. J. Wilkinson. 2006. Autolytic properties of glycopeptide-intermediate Staphylococcus aureus Mu50. Antimicrob. Agents Chemother,50:1541-1545.�
[9] Sieradzki, K., and A. Tomasz. 2003. Alterations of cell wall structure and 136 HOWDEN ET AL. CLIN. MICROBIOL. REV.Downloaded from cmr.省略 at Univ of Idaho on January 22, 2010 metabolism accompany reduced susceptibility to vancomycin in an isogenic series of clinical isolates of Staphylococcus aureus. J. Bacteriol,185:7103-7110.�
[10] Koehl, J. L., A. Muthaiyan, R. K. Jayaswal, K. Ehlert, H. Labischinski, and B. J. Wilkinson. 2004. Cell wall composition and decreased autolytic activity and lysostaphin susceptibility of glycopeptide-intermediate Staphylococcus aureus. Antimicrob. Agents Chemother,48:3749-3757.�
[11] Nelson, J. L., K. C. Rice, S. R. Slater, P. M. Fox, G. L. Archer, K. W. Bayles, P. D. Fey, B. N. Kreiswirth, and G. A. Somerville. 2007. Vancomycinintermediate Staphylococcus aureus strains have impaired acetate catabolism: implications for polysaccharide intercellular adhesin synthesis and autolysis. Antimicrob. Agents Chemother. 51:616-622.�
[12] Sakoulas G,Moellering RC Jr,Eliopoulos GM.Adaptation of methicillin-resistant Staphylococcus aureus in the face of vancomycin therapy.Clin.Infect.Dis,2006,42:40-50.�
[13] Wootton M, Avison MB,Bennett PM,et al. Genetic analysis of 17 genes in Staphylococcus aureus with reduced susceptibility to vancomycin and hetero-VISA.J antimicrob Chemother,2004,53(2):406-407.�
[14] Huebner, J., A. Kropec, I. Engels, and F. Daschner. In vitro susceptibility of methicillin-resistant Staphylococcus aureus and slime-producing and non-slime-producing coagulase-negative staphylococci to fusidic acid. Chemotherapy,1992,38:206-210.�
[15] Howden, B. P., P. B. Ward, P. D. Johnson, P. G. Charles, and M. L. Grayson.Low-level vancomycin resistance in Staphylococcus aureus-an Australian perspective. Eur. J. Clin. Microbiol. Infect. Dis,2005,24:100-108.�
[16] Howden, B. P., P. B. Ward, P. G. Charles, T. M. Korman, A. Fuller, P. Du Cros, E. A. Grabsch, S. A. Roberts, J. Robson, K. Read, N. Bak, J. Hurley, P. D. Johnson, A. J. Morris, B. C. Mayall, and M. L. Grayson. Treatment outcomes for serious infections caused by methicillin-resistant Staphylococcus aureus with reduced vancomycin susceptibility. Clin. Infect. Dis,2004,38:521-528.�
[17] Jevitt, L. A., A. J. Smith, P. P. Williams, P. M. Raney, J. E. McGowan, Jr., and F. C. Tenover. In vitro activities of daptomycin, linezolid, and quinupristin-dalfopristin against a challenge panel of staphylococci and enterococci, including vancomycin-intermediate Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Microb. Drug Resist,2003,9:389-393.�
[18] Kola, A., P. Kirschner, B. Gohrbandt, I. F. Chaberny, F. Mattner, M. Struber, P. Gastmeier, and S. Suerbaum. An infection with linezolidresistant S. aureus in a patient with left ventricular assist system. Scand. J. Infect. Dis,2007,39:463-465.�
[19] Tillotson, G. S., D. C. Draghi, D. F. Sahm, K. M. Tomfohrde, T. Del Fabro, and I. A. Critchley. Susceptibility of Staphylococcus aureus isolated from skin and wound infections in the United States 2005-07: laboratorybased surveillance study. J. Antimicrob. Chemother,2008,62:109-115.�
[20] Bishop, E., S. Melvani, B. P. Howden, P. G. Charles, and M. L. Grayson. Good clinical outcomes but high rates of adverse reactions during linezolid therapy for serious infections: a proposed protocol for monitoring therapy in complex patients. Antimicrob. Agents Chemother,2006,50:1599-1602.�
[21] Muthaiyan A,Silverman JA,Ayaswal RK,et al. Transcriptional profiling reveals that daptomycin induces the Staphylococcus aureus cell wall stress stimulon and genes responsive to memvrane depolarization.Antimicrob Agents Chemother,2008,52(3):980-990.�
[22] Hirschwerk, D., C. C. Ginocchio, M. Bythrow, and S. Condon. Diminished susceptibility to daptomycin accompanied by clinical failure in a patient with methicillin-resistant Staphylococcus aureus bacteremia. Infect. Control Hosp. Epidemiol,2006,27:315-317.�
[23] Samra, Z., O. Ofir, and H. Shmuely.In vitro susceptibility of methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium to daptomycin and other antibiotics. Eur. J. Clin. Microbiol. Infect. Dis,2007,26:363-365.�
[24] Jevitt, L. A., A. J. Smith, P. P. Williams, P. M. Raney, J. E. McGowan, Jr., and F. C. Tenover. In vitro activities of daptomycin, linezolid, and quinupristin-dalfopristin against a challenge panel of staphylococci and enterococci, including vancomycin-intermediate Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Microb. Drug Resist,2003,9:389-393.�
[25] Huang, Y. T., C. H. Liao, L. J. Teng, and P. R. Hsueh. Comparative bactericidal activities of daptomycin, glycopeptides, linezolid and tigecycline against blood isolates of Gram-positive bacteria in Taiwan. Clin. Microbiol. Infect,2008,14:124-129.�
[26] 杨惠娣,徐彬. 糖肽类抗菌药物oritavancin 和dalbavancin 的开发应用. 世界临床药物,2005 ,26 (11) :666-669.�
[27] Streit, J. M., H. S. Sader, T. R. Fritsche, and R. N. Jones.Dalbavancin activity against selected populations of antimicrobial-resistant Grampositive pathogens. Diagn. Microbiol. Infect. Dis,2005,53:307-310.�
[28] Sader, H. S., T. R. Fritsche, K. Kaniga, Y. Ge, and R. N. Jones. Antimicrobial activity and spectrum of PPI-0903M (T-91825), a novel cephalosporin, tested against a worldwide collection of clinical strains. Antimicrob. Agents Chemother,2005,49:3501-3512.�
[29] Bogdanovich, T., L. M. Ednie, S. Shapiro, and P. C. Appelbaum. Antistaphylococcal activity of ceftobiprole, a new broad-spectrum cephalosporin. Antimicrob. Agents Chemother,2005,49:4210-4219.�
[30] Draghi, D. C., M. Jones, C. Thornsberry, R. K. Flamm, and D. F. Sahm. Telavancin activity against current and diverse Staphylococcus aureus populations, abstr. E-1744. Abstr. 45th Intersci. Conf. Antimicrob. Agents Chemother.��
