Related Experiment Video
Updated: Feb 27, 2026
Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Published on: May 8, 2013
Next-Generation Sequence Analysis Reveals Transfer of Methicillin Resistance to a Methicillin-Susceptible
Veronica Weterings1,2, Thijs Bosch3, Sandra Witteveen3
1Laboratory for Microbiology and Infection Control, Amphia Hospital, Breda, The Netherlands vweterings@amphia.nl.
Abstract:
Resistance to methicillin in Staphylococcus aureus is caused primarily by the mecA gene, which is carried on a mobile genetic element, the staphylococcal cassette chromosome mec (SCCmec). Horizontal transfer of this element is supposed to be an important factor in the emergence of new clones of methicillin-resistant Staphylococcus aureus (MRSA) but has been rarely observed in real time. In 2012, an outbreak occurred involving a health care worker (HCW) and three patients, all carrying a fusidic acid-resistant MRSA strain. The husband of the HCW was screened for MRSA carriage, but only a methicillin-susceptible S. aureus (MSSA) strain, which was also resistant to fusidic acid, was detected. Multiple-locus variable-number tandem-repeat analysis (MLVA) typing showed that both the MSSA and MRSA isolates were MT4053-MC0005. This finding led to the hypothesis that the MSSA strain acquired the SCCmec and subsequently caused an outbreak. To support this hypothesis, next-generation sequencing of the MSSA and MRSA isolates was performed. This study showed that the MSSA isolate clustered closely with the outbreak isolates based on whole-genome multilocus sequence typing and single-nucleotide polymorphism (SNP) analysis, with a genetic distance of 17 genes and 44 SNPs, respectively. Remarkably, there were relatively large differences in the mobile genetic elements in strains within and between individuals. The limited genetic distance between the MSSA and MRSA isolates in combination with a clear epidemiologic link supports the hypothesis that the MSSA isolate acquired a SCCmec and that the resulting MRSA strain caused an outbreak.
Insights
A methicillin-susceptible Staphylococcus aureus strain acquired the staphylococcal cassette chromosome mec (SCCmec) element, leading to a methicillin-resistant Staphylococcus aureus (MRSA) outbreak. This demonstrates real-time horizontal gene transfer driving MRSA emergence.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Methicillin resistance in Staphylococcus aureus (MRSA) is primarily mediated by the mecA gene located on the staphylococcal cassette chromosome mec (SCCmec).
- Horizontal transfer of SCCmec is a key factor in the emergence of new MRSA clones, but has rarely been observed in real-time.
Purpose of the Study:
- To investigate the potential horizontal transfer of SCCmec from a methicillin-susceptible S. aureus (MSSA) strain to an MRSA strain during a healthcare-associated outbreak.
- To elucidate the genetic mechanisms underlying the emergence of a specific MRSA clone.
Main Methods:
- Multiple-locus variable-number tandem-repeat (MLVA) analysis to compare MSSA and MRSA isolates.
- Next-generation sequencing (NGS) for whole-genome multilocus sequence typing (wgMLST) and single-nucleotide polymorphism (SNP) analysis.
- Comparative analysis of mobile genetic elements between isolates.
Main Results:
- Both MSSA and MRSA isolates belonged to the same MLVA type (MT4053-MC0005).
- wgMLST and SNP analysis revealed a close genetic relationship between the MSSA and MRSA isolates (17 genes and 44 SNPs difference).
- Significant variations in mobile genetic elements were observed within and between individuals.
Conclusions:
- The findings strongly support the hypothesis that the MSSA strain acquired the SCCmec element, resulting in the emergence of the MRSA strain responsible for the outbreak.
- This study provides rare real-time evidence of SCCmec horizontal transfer driving MRSA clonal expansion.
Related Concept Videos
01:29Modern Molecular Taxonomy
01:30Development of Antibiotic Resistance
00:57Antibiotic Selection
01:36Mismatch Repair