Comparison of Molecular Typing Methods for Characterization of Staphylococcus epidermidis : Proposal for Clone Definition

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Abstract
In the present study we give some direction on the selection of the most appropriate typing method(s) to be used for the characterization of Staphylococcus epidermidis , in view of the most recent findings on the evolution, population structure, and epidemiology of this species. In order to achieve this aim, quantitative assessment of the correlation of the results of three typing methods—pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and staphylococcal chromosomal cassette mec (SCC mec ) typing, which target different regions of the chromosome that evolve at different rates—was performed. In order to evaluate the discriminatory ability and the strength and direction of the correlation of the different typing methods, Simpson's index of diversity (SID), the adjusted Rand coefficient (AR), and the Wallace coefficient ( W ) were calculated. PFGE was the most discriminatory method (SID = 99%), followed by MLST (SID = 90%) and SCC mec typing (SID = 75%). The values of AR and W (0.10 < AR < 0.30; 0.50 < W < 0.75) indicated that the partition of the same isolate collection by PFGE, MLST, and SCC mec typing provided results that had only a poor correlation with each other. However, the information provided by the combination of PFGE and SCC mec enabled the prediction of the results obtained by MLST at the level of the clonal complex with a high degree of precision ( W > 0.90). We propose that clones of S. epidermidis be defined by the combination of the PFGE type followed by the SCC mec type, which provides reliable information on the short-term epidemiology and the ability to predict with consistency long-term clonal evolution.

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