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Open Access Highly Accessed Research article

Molecular typing and characterization of nasal carriage and community-onset infection methicillin-susceptible Staphylococcus aureus isolates in two Taiwan medical centers

Feng-Jui Chen1, Leung-Kei Kristopher Siu12*, Jung-Chung Lin3, Chen-Her Wang1 and Po-Liang Lu45*

Author Affiliations

1 Division of Infectious Diseases, National Health Research Institutes, Zhunan, Taiwan

2 Graduate Institute of Basic Medical Science, China Medical University, Taichung, Taiwan

3 Department of Internal Medicine, Division of Infectious Diseases and Tropical Medicine, Tri-Service General Hospital, Taipei, Taiwan

4 Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan

5 School of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan

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BMC Infectious Diseases 2012, 12:343  doi:10.1186/1471-2334-12-343

Published: 10 December 2012

Abstract

Background

Compared to methicillin-resistant Staphylococcus aureus (MRSA), characteristics of nasal carriage and community-onset infection methicillin-susceptible S. aureus (MSSA) are less well known. No characteristics of MSSA in Taiwan have been reported previously.

Methods

We analyzed 100 nasal carriage and 34 community-onset infection MSSA isolates by pulsed-field gel electrophoresis (PFGE), spa typing, multi-locus sequence typing, agr typing, virulence gene detection, growth rate measurement, and antimicrobial susceptibility.

Results

In PFGE analysis, most (68%) infection isolates could be grouped in one major cluster using a 70% similarity cutoff. In contrast, only 17% of nasal carriage isolates belonged to this cluster. A similar classification was obtained using Based Upon Repeat Pattern analysis of spa types. The MSSA infection isolates cluster was closely related to the virulent clones of clonal complex 1 (CC1), which includes strains MW2 (USA400) and MSSA476. ST188 of CC1 was the predominant clone detected for community-onset MSSA infections. The only common ST type for MSSA and MRSA in Taiwan was ST59, the community-associated MRSA clone. It is likely, therefore, that MRSA originated from MSSA clones through SCCmec transfer. Compared to nasal carriage isolates, infection isolates less frequently possessed egc, tst and hlg genes, were more commonly susceptible to erythromycin (91% vs. 54%), and had shorter mean doubling times (38 min vs. 55 min).

Conclusions

The clonal lineages of MSSA nasal carriage and infection isolates differed in our sample of Taiwan isolates. Most community-onset MSSA infections resulted from relatively few clonal lineages. Nasal carriage isolates more frequently possessed the egc, tst and hlg genes, were more resistant to erythromycin, and grew more slowly.

Keywords:
Nasal carriage; Community onset; Infection; MSSA; Staphylococcus aureus; Lineage; Pulsed-field gel electrophoresis; Multi-locus sequence typing; Spa typing