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Updated: Mar 8, 2026
Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Published on: May 8, 2013
Re-emergence of methicillin susceptibility in a resistant lineage of Staphylococcus aureus
Alice Ledda1, James R Price2, Kevin Cole2,3
1Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London W2 1PG, UK.
Objectives:
MRSA is a leading cause of hospital-associated infection. Acquired resistance is encoded by the mecA gene or its homologue mecC , but little is known about the evolutionary dynamics involved in gain and loss of resistance. The objective of this study was to obtain an expanded understanding of Staphylococcus aureus methicillin resistance microevolution in vivo , by focusing on a single lineage.
Methods:
We compared the whole-genome sequences of 231 isolates from a single epidemic lineage [clonal complex 30 (CC30) and spa -type t018] of S. aureus that caused an epidemic in the UK.
Results:
We show that resistance to methicillin in this single lineage was gained on at least two separate occasions, one of which led to a clonal expansion around 1995 presumably caused by a selective advantage. Resistance was, however, subsequently lost in vivo by nine strains isolated between 2008 and 2012. We describe the genetic mechanisms involved in this loss of resistance and the imperfect relationship between genotypic and phenotypic resistance.
Conclusions:
The recent re-emergence of methicillin susceptibility in this epidemic lineage suggests a significant fitness cost of resistance and reduced selective advantage following the introduction in the mid-2000s of MRSA hospital control measures throughout the UK.
Insights
Methicillin-resistant Staphylococcus aureus (MRSA) resistance was gained and lost multiple times within a single lineage. This suggests a fitness cost to MRSA, especially after control measures were implemented.
Area of Science:
- Microbiology
- Genetics
- Evolutionary dynamics
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of hospital-associated infections.
- The genetic basis of MRSA resistance involves the mecA gene or its homologue mecC.
- Understanding the evolutionary dynamics of resistance gain and loss in MRSA is crucial.
Purpose of the Study:
- To investigate the microevolution of methicillin resistance in Staphylococcus aureus within a single lineage.
- To understand the in vivo evolutionary dynamics of MRSA resistance gain and loss.
Main Methods:
- Whole-genome sequencing of 231 Staphylococcus aureus isolates from a single epidemic lineage (CC30, spa-type t018) in the UK.
- Analysis of genetic mechanisms underlying resistance gain and loss.
Main Results:
- Methicillin resistance was gained at least twice within the studied lineage, with one instance leading to clonal expansion around 1995.
- Nine strains lost methicillin resistance in vivo between 2008 and 2012.
- The study identified genetic mechanisms for resistance loss and highlighted an imperfect correlation between genotypic and phenotypic resistance.
Conclusions:
- The re-emergence of methicillin susceptibility in this MRSA lineage indicates a substantial fitness cost associated with resistance.
- Reduced selective advantage of MRSA was observed following the implementation of UK-wide hospital control measures in the mid-2000s.
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