Analysis of typing methods for epidemiological surveillance of both methicillin-resistant and methicillin-susceptible Staphylococcus aureus strains

Abstract

Sequence-based methods for typing Staphylococcus aureus, such as multilocus sequence typing (MLST) and spa typing, have increased interlaboratory reproducibility, portability, and speed in obtaining results, but pulsed-field gel electrophoresis (PFGE), remains the method of choice in many laboratories due to the extensive experience with this methodology and the large body of data accumulated using the technique. Comparisons between typing methods have been overwhelmingly based on a qualitative assessment of the overall agreement of results and the relative discriminatory indexes. In this study, we quantitatively assess the congruence of the major typing methods for S. aureus, using a diverse collection of 198 S. aureus strains previously characterized by PFGE, spa typing, MLST, and, in the case of methicillin-resistant S. aureus (MRSA), SCCmec typing in order to establish the quantitative congruence between the typing methods. The results of most typing methods agree in that MRSA and methicillin-susceptible S. aureus (MSSA) differ in terms of diversity of genetic backgrounds, with MSSA being more diverse. Our results show that spa typing has a very good predictive power over the clonal relationships defined by eBURST, while PFGE is less accurate for that purpose but nevertheless provides better typeability and discriminatory power. The combination of PFGE and spa typing provided even better results. Based on these observations, we suggest the use of the conjugation of spa typing and PFGE typing for epidemiological surveillance studies, since this combination provides the ability to infer long-term relationships while maintaining the discriminatory power and typeability needed in short-term studies.

FIG. 1.

Representation of correspondences between typing methods and combinations of typing methods used in the 198-strain collection, calculated by W coefficients. The arrows represent W coefficients of >0.60, excluding the obvious relationships.

FIG. 2.

Representation of correspondences between typing methods and combinations of typing methods used in the 116-strain MRSA subset, calculated by W coefficients. The arrows represent W coefficients of >0.60, excluding the obvious relationships.

FIG. 3.

Representation of correspondences between typing methods and combinations of typing methods used in the 82-strain MSSA subset, calculated by W coefficients. The arrows represent W coefficients of >0.60, excluding the obvious relationships.