The MLST data used by eBURST are the STs and their associated
allelic profiles. The first step is to divide the input data
(e.g. the isolates within a MLST database) into groups of
STs that have some user-defined level of similarity in allelic
profile, since eBURST focuses on those STs that are similar
and which may share descent from the same founding genotype,
and provides no information about the more distant relationships
The definition of the group can be changed,
but the default eBURST setting is to identify groups of related
STs using the most stringent (conservative) definition, where
all members assigned to the same group share identical alleles
at = 6 of the 7 loci with at least one other member of the
group. A less stringent approach is to define the groups
by the sharing of alleles at = 5 of the 7 loci. Whatever
group definition is used, this approach results in non-overlapping
groups; no ST can be assigned to more than one group.
A ’group’ is used here as a
neutral term for the collection of STs that are placed together
by eBURST, according to the selected group definition, whereas
a clonal complex is a set of STs that are all believed to
be descended from the same founding genotype. Using the stringent
group definition (6/7 shared alleles), isolates in the group
defined by eBURST will be considered to belong to a single
clonal complex. With a less stringent group definition (e.g.
5/7 shared alleles) all of the STs in an eBURST group cannot
be assumed to belong to a single clonal complex.
The eBURST applet is designed for MLST data,
which typically uses seven loci, but there is an option to
change the number of loci, and the number of shared alleles
used to define a group can also be changed to an appropriate
number within the applet window.