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Subcutaneous Infection of Methicillin Resistant Staphylococcus Aureus (MRSA)
Published on: February 9, 2011
Severe Staphylococcus aureus infections caused by clonally related community-acquired methicillin-susceptible and
Kanokporn Mongkolrattanothai1, Susan Boyle, Madelyn D Kahana
1Section of Pediatric Infectious Diseases, University of Chicago, Department of Pediatrics, Chicago, Illinois 60637, USA.
Abstract:
We investigated the genetic relatedness of 5 community-acquired (CA) Staphylococcus aureus isolates obtained from 4 consecutive pediatric patients presenting with sepsis syndrome and severe pneumonia during a 3-week period in 2000. Two patients were infected with methicillin-susceptible S. aureus (MSSA), and 2 were infected with methicillin-resistant S. aureus (MRSA). The pulsed-field gel electrophoresis patterns for the 2 CA-MRSA isolates were identical to each other, as were the patterns for the 3 CA-MSSA isolates. A 2-band difference reflecting the presence of a staphylococcal cassette chromosome mec (SCCmec) element distinguished the CA-MRSA isolates from the CA-MSSA isolates. The small, mobile type IV SCCmec element was present in the CA-MRSA isolates. These data suggest that an insertion or, less likely, a deletion of the SCCmec type IV element occurred in a highly virulent S. aureus background. Staphylococcal toxin genes sea, seh, lukS-PV, and lukF-PV were detected in all isolates. Also, in all isolates, was a partial homolog of seo (seo'). The relationship among these patient isolates strengthens the assumption that CA-MRSA infections may be caused by isolates closely related to MSSA isolates.
Insights
Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections may stem from strains closely related to methicillin-susceptible S. aureus (MSSA). Genetic analysis revealed a mobile staphylococcal cassette chromosome mec (SCCmec) element differentiating these strains.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Community-acquired Staphylococcus aureus (CA-SA) infections pose a significant public health concern, particularly in pediatric populations.
- Distinguishing between methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains is crucial for effective treatment and infection control.
- Understanding the genetic basis of virulence and resistance in CA-SA is essential for developing targeted interventions.
Purpose of the Study:
- To investigate the genetic relatedness of community-acquired Staphylococcus aureus (CA-SA) isolates from pediatric patients with sepsis and pneumonia.
- To determine the genetic factors contributing to methicillin resistance in these CA-SA isolates.
- To explore the potential clonal relationship between CA-MRSA and CA-MSSA strains.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) was employed to analyze the genetic profiles of five CA-SA isolates.
- Staphylococcal cassette chromosome mec (SCCmec) typing was performed to identify the presence and type of the resistance element.
- Detection of specific staphylococcal toxin genes (sea, seh, lukS-PV, lukF-PV, seo') was conducted using molecular techniques.
Main Results:
- PFGE revealed distinct genetic patterns for CA-MRSA and CA-MSSA isolates, with identical patterns within each group.
- The presence of a type IV staphylococcal cassette chromosome mec (SCCmec) element was identified in CA-MRSA isolates, differentiating them from CA-MSSA isolates.
- All investigated isolates, regardless of methicillin susceptibility, harbored common staphylococcal toxin genes (sea, seh, lukS-PV, lukF-PV) and a partial homolog of seo (seo').
Conclusions:
- The genetic similarity between CA-MRSA and CA-MSSA isolates suggests that CA-MRSA may have emerged from highly virulent MSSA strains through the acquisition of the SCCmec element.
- The mobile nature of the type IV SCCmec element likely played a role in the development of CA-MRSA infections.
- The presence of shared virulence factors across both MRSA and MSSA isolates highlights the complex interplay of resistance and pathogenicity in Staphylococcus aureus infections.
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