Sequence Analysis of the Variable Number Tandem Repeat in Staphylococcus aureus Protein A Gene - Bacterial Pathogenesis: Methods and Protocols - page 282

Fig. 5. Bayesian reconstruction of Staphylococcus aureus phylogeny based on
concatenated sequences of MLST gene fragments, adapted from reference (49) . The
three proposed groups (1a, 1b, and 2) are highlighted and the MLST sequence types
corresponding to each branch labeled. Individual spa types associated with ST8 are
indicated, corresponding to the “tips” of the ST8 branch; the phylogenetic relationships
are undetermined, so no topology is depicted. Additional spa types can be assigned
similarly to the other branches (not shown). Pulsed-field gel electrophoresis patterns for
different spa type 1 and 7 strains are shown, depicting the potential variation underlying
defined spa types, and corresponding to the “leaves” on the tips of the branches.
observed changes. That is, are two strains that differ by a single point mutation,
such as spa types 1 and 7, more closely related than strains 1 and 363 (which
differ by a single repeat) or strains 1 and 59 (which differ by two repeats)
or are they equivalent under the hypothesis that each of these genetic alter-
ations represent single events? A study by Robinson and Enright examined
the relationship between seven housekeeping MLST gene targets and eight
surface protein encoding genes (7 sas genes and spa ) among 220 isolates repre-
senting major lineages of nosocomial MRSA, MSSA, and CA-MRSA (32) .
Here, results of spa typing were concordant with the grouping of MLST and sas
gene targets. This study also lends credence to the idea that one can infer MLST
results on the basis of spa -typing data, an assumption that will be evaluated
over time as both methods continue to be used by S. aureus researchers.