Catalano M
Departamento de Microbiología, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
Medicina (B Aires). 1994;54(5 Pt 2):596-604.
Hospitalized patients are at unusually high risk of infections, and furthermore, the hospital environment favors the acquisition of resistance to antimicrobial agents, complicating the treatment of nosocomial infections due to drug-resistant pathogens. The prevention of nosocomial infections, based on a surveillance system as an essential element of an infection control program, is the only way to reduce morbidity and mortality. A typing method for strain clonality permits the infection control program to confirm the association between infected patients and the reservoir for the microorganisms of interest and to determine modes of transmission, because the mode of transmission or reservoir may not be the same for multiple strains of a bacterial species. An ideal method of subtyping bacterial isolates from a given species should be simple, rapid, sensitive and discriminatory. Traditionally, once bacterial isolates from an outbreak have been determined to be of the same species, further evaluation for similarity or relatedness has been based on phenotypic methods. Biotyping, serotyping, phagetyping, and antibiotype determination are not always adequately sensitive to distinguish unrelated strains with similar phenotypes. Within phenotypic methods, multilocus enzyme electrophoresis is a powerful tool but because of its complexity it is not likely to become widely available for study of local outbreaks of bacterial infections. In recent years, molecular genetic methods, including plasmid profile, genomic restriction fragment length polymorphism analyses by conventional electrophoresis or by pulsed-field gel electrophoresis, single chromosomal gene polymorphism by DNA hybridization or by PCR amplification, ribotyping, and genomic fingerprinting generated by repetitive element sequence-based polymerase chain reaction, have been useful in evaluating endemic infections and outbreaks of a variety of nosocomial pathogens. For epidemiologic studies, genotyping systems based on defined chromosomal genes or whole DNA polymorphism provide significant advantages over plasmid analysis. Among plasmid-non-based genotypic methods, the choice depends on i) the examination of how much discrimination the method can add for the epidemiologic investigation, ii) the resources available to the laboratory, and iii) the level of expertise of the personnel involved in the testing because, until standardized rules of interpretation are published, the same data may be interpreted in different ways by different investigators. Finally, biotyping, serotyping, and antibiotype determination remain an appropriate first step for the evaluation of apparent outbreaks with the caveat that different strains with the same phenotypic properties may exist concurrently within the same environment. Genotyping may be a second level of analysis to evaluate relatedness of bacterial strains, because the use of molecular biology techniques should support an epidemiologic investigation rather than initiate it.
住院患者面临着异常高的感染风险，此外，医院环境有利于获得对抗菌药物的耐药性，这使得耐药病原体引起的医院感染的治疗变得更加复杂。基于监测系统作为感染控制计划的基本要素来预防医院感染，是降低发病率和死亡率的唯一途径。一种用于菌株克隆性分型的方法能使感染控制计划确认感染患者与目标微生物储存源之间的关联，并确定传播方式，因为对于一个细菌物种的多个菌株来说，传播方式或储存源可能并不相同。一种理想的对给定物种的细菌分离株进行亚型分型的方法应该简单、快速、灵敏且具有鉴别力。传统上，一旦确定来自一次暴发的细菌分离株属于同一物种，对于相似性或相关性的进一步评估就基于表型方法。生化分型、血清分型、噬菌体分型和抗菌型测定并不总是足够灵敏，无法区分具有相似表型的不相关菌株。在表型方法中，多位点酶电泳是一种强大的工具，但由于其复杂性，它不太可能广泛用于研究局部细菌感染暴发。近年来，分子遗传学方法，包括质粒图谱分析、通过常规电泳或脉冲场凝胶电泳进行的基因组限制性片段长度多态性分析、通过DNA杂交或PCR扩增进行的单染色体基因多态性分析、核糖体分型以及基于重复元件序列的聚合酶链反应产生的基因组指纹分析，已被用于评估多种医院病原体的地方性感染和暴发。对于流行病学研究，基于特定染色体基因或全DNA多态性的基因分型系统比质粒分析具有显著优势。在非基于质粒的基因分型方法中，选择取决于：i）该方法能为流行病学调查增加多少鉴别力；ii）实验室可用的资源；iii）参与检测人员的专业水平，因为在发布标准化的解释规则之前，不同的研究者可能会以不同的方式解释相同的数据。最后，生化分型、血清分型和抗菌型测定仍然是评估明显暴发的合适第一步，但需要注意的是，在同一环境中可能同时存在具有相同表型特征的不同菌株。基因分型可能是评估细菌菌株相关性的第二级分析，因为分子生物学技术的使用应该支持而不是启动流行病学调查。
