Over the years, approaches to the epidemiological analysis of infectious disease have undergone a remarkable evolutionary transition moving from phenotypic to molecular in nature. As discussed here, the quest for a clearer comparison of genomic relatedness between bacterial clinical isolates has involved four generations of molecular iteration. First generation plasmid analysis gave way to a second generation use of restriction enzymes and probes. This was followed by third generation pulsed field gel electrophoresis (PFGE) and PCR-based methods with movement now to fourth-generation DNA sequence-based approaches. Remarkably, despite (or perhaps because of) its more than 20-year history as a typing method, PFGE has demonstrated exceptional staying power. The reasons for this endurance as well as the pros and cons of PFGE use are examined in this review. In broad context the history and technology behind PFGE are considered. Issues commonly influencing the quality of PFGE data and its analysis are discussed. Specifics regarding the mechanics of DNA preparation, restriction-enzyme digestion, and proper conditions for electrophoresis are detailed and, most importantly for any approach to epidemiological assessment, issues regarding the analysis and interpretation of PFGE data are explored.
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