Figure 1

Comparison of resolution of typing techniques. Typing methods range in resolution, from low resolution, which can classify isolates as indistinguishable (I) from the index case (X), closely related (C, C₁, and C₂) or very different (D), to the high-resolution method of genome sequencing, which can distinguish isolates by single nucleotide variation. Isolates indistinguishable by lower-resolution techniques may be distinguishable by their sequences; indistinguishable by complete whole genome sequencing is by definition having the identical sequence. (a-d) Schematic representations of pulsed-field gel electrophoresis (PFGE) (a), seroptying (using the example of serotypes of Streptococcus pneumoniae) (b), multilocus sequence typing (MLST; in cartoon eBURST figure) (c), and a phylogeny from whole genome sequencing (d) show the different levels of resolution. Whereas in PFGE, serotype and MLST, isolates can be identified as at coarse levels of relatedness, genotyping offers higher-resolution typing. An isolate seen as closely related (C₁) to the index case (X) in whole genome sequencing may be indistinguishable (I) in the first three methods, whereas a more distantly related isolate, as seen by whole genome sequencing (C₂), might appear as closely related. Moreover, as described in the text, the integration of sequencing with molecular evolutionary theory provides much greater opportunity for phylogenetic inference, offering conceptual leaps beyond other typing methods and greater contributions to infectious disease epidemiology.