Aucken H M, Boquete T, Kaufmann M E, Pitt T L
Laboratory of Hospital Infection, Central Public Health Laboratory, London, UK.
Epidemiol Infect. 2000 Aug;125(1):63-70. doi: 10.1017/s0950268899004112.
The number of band differences in DNA macrorestriction profiles required to distinguish unrelated strains from an index strain varies in an outbreak with the species and restriction enzyme used. In order to define this difference for epidemiological studies of Serratia marcescens, we produced DNA fingerprints from 57 isolates of the organism using the restriction enzyme XbaI and pulsed-field gel electrophoresis (PFGE). The isolates were selected on the basis of their epidemiology, serotype and phage-typing patterns to include 28 unrelated strains and 29 representatives from 2 distinct outbreaks. One of the outbreaks was prolonged. lasting for several years. Electrophoretic profiles consisting of 20 or more clearly resolved bands were obtained for all isolates. Twenty-six of the unrelated strains had unique profiles with over 10 band differences from all other strains, while 27 of the outbreak representatives could be assigned to the appropriate outbreak with confidence. The majority of the outbreak isolates had none or 2 band differences from the index profile, although 3 isolates differed by 5-7 bands. The 2 exceptions among the unrelated strains differed by 4 bands, and 3 phage typing reactions, and were isolated from London and Berlin 3 years apart, while the 2 exceptions among the outbreak collection had clearly unique profiles with over 20 band differences from each other and the outbreak profiles. Cluster analysis using Dice coefficient and UPGMA gave cut-off values of 75-78% similarity overall for related isolates, while the closest similarity for unrelated strains was 70%. The results of this study together with those of the 6 previous reports of PFGE for S. marcescens (which used either enzymes XbaI or SpeI) confirm that this technique is of value for this species and that with XbaI at least, most epidemiologically related strains will only differ by 3-4 bands. However, on occasion up to 7 band differences can be found within an apparent outbreak, which may be suggestive of genetic drift.
在一次暴发中，区分无关菌株与指示菌株所需的DNA宏观限制性图谱中的条带差异数量会因所用的菌种和限制性内切酶而有所不同。为了在粘质沙雷氏菌的流行病学研究中确定这种差异，我们使用限制性内切酶XbaI和脉冲场凝胶电泳（PFGE）对该菌的57株分离株进行了DNA指纹图谱分析。这些分离株是根据其流行病学、血清型和噬菌体分型模式挑选出来的，包括28株无关菌株和来自2次不同暴发的29株代表菌株。其中一次暴发持续时间较长，长达数年。所有分离株均获得了由20条或更多清晰可辨条带组成的电泳图谱。26株无关菌株具有独特的图谱，与所有其他菌株有超过10条带的差异，而27株暴发代表菌株能够被可靠地归入相应的暴发。大多数暴发分离株与指示图谱没有条带差异或只有2条带的差异，不过有3株分离株相差5 - 7条带。无关菌株中的2个例外相差4条带和3次噬菌体分型反应，且相隔3年分别从伦敦和柏林分离得到，而暴发菌株中的2个例外具有明显独特的图谱，彼此之间以及与暴发图谱有超过20条带的差异。使用Dice系数和UPGMA进行聚类分析得出，相关分离株总体相似性的截止值为75 - 78%，而无关菌株之间的最接近相似性为70%。本研究结果以及之前6篇关于粘质沙雷氏菌PFGE的报告（使用XbaI或SpeI酶）的结果证实，该技术对该菌种有价值，并且至少使用XbaI时，大多数流行病学相关菌株只会相差3 - 4条带。然而，在明显的一次暴发中偶尔会发现多达7条带的差异，这可能暗示着基因漂移。
