Molecular typing of Salmonella enterica serovar Typhimurium

沙门氏菌主要引起食物中毒，是一个重大的人类健康问题。不同的沙门氏菌形式通过血清分型来鉴定，并且许多血清型已经被命名。有2000多个血清型。最著名的血清型是鼠伤寒，它是40%沙门氏菌感染的原因。鼠伤寒是如此频繁地参与感染，有必要进一步划分它的爆发调查和长期监测的有机体。唯一广泛使用的细分鼠伤寒的方法是噬菌体分型，仅在主要实验室（澳大利亚2个）进行。噬菌体分型基于测试分离株对一组34个噬菌体的裂解模式。噬菌体分型在追踪生物体方面发挥了至关重要的作用，例如在英国和美国出现了多药耐药的新型（DT 204c）。该技术很简单，但问题是，反应随条件的微小变化而变化，并且对反应结果进行评分是非常主观的。我们建议用一种基于DNA方法PCR的分型系统来代替传统的分型系统，从而使它变得简单、快速和准确。我们将使用一种称为AFLP（扩增片段长度多态性）的DNA指纹技术来寻找特异于噬菌体类型的标记（DNA片段），并根据我们发现的标记设计PCR检测。这样的分型系统将通过提供关于噬菌体类型的有价值的流行病学数据库的连续性来保留噬菌体分型的本质。此外，分型系统可以很容易地扩展，以适应任何新的类型，通过找到更多的标记，而目前的噬菌体分型系统是非常难以扩大（最后完成于1977年，是落后于我们的需要）。该项目将建立一个通用的方法来设计基于分子生物学的其他病原体的分型系统，并可能对21世纪的细菌感染监测产生重大影响。

Salmonella mainly causes food poisoning and is a significant human health problem. Different Samonella forms are identified by serotyping and many serovars have been given a name . There are more than 2000 serovars. The best known serovar is Typhimurium which is the cause of 40% of salmonella infections. Typhimurium is so frequently involved in infections it is necessary to further divide it for outbreak investigations and long term monitoring of the organism. The only widely used method to subdivide Typhimurium is phage typing, which is done only in major laboratories (2 in Australia). Phage typing is based on lysis patterns of a test isolate to a set of 34 phages. Phage typing has played a crucial role in tracking the organism, for example the emergence of a multidrug resistance new type (DT204c) in UK and US. The technique is simple but the problem is that reactions vary with slight change in conditions and scoring the reaction results is very subjective. We propose to replace the typing system with one based on the DNA method PCR, so it will be simple, fast and accurate. We will use a DNA fingerprinting technique called AFLP (amplified fragment length polymorphism) to find markers (DNA segments) that are specific to phage types and design PCR assays based on the markers we find. Such a typing system will retain the essence of phage typing by providing continuity of the valuable epidemiological database on phage types. Further the typing system could easily be expanded to accommodate any new types by finding more markers while the current phage typing system is very difficult to expand (last done in 1977 and is behind in our needs). This project will establish a general approach for designing typing systems based on molecular biology for other pathogens and could have a major impact on the surveillance of bacterial infections in the 21st century.