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Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Staphylococcal Cassette Chromosome mec Typing and Multilocus Variable Number Tandem Repeat Analysis of Methicillin
Faiqa Arshad1, Sidrah Saleem1, Romeeza Tahir2
1Department of Microbiology, University of Health Sciences, Lahore, Punjab, Pakistan.
Background:
The association of treatment failure and mortality with vancomycin minimum inhibitory concentration creep (MIC) is a matter of serious concern in patients with severe methicillin resistant Staphylococcus aureus (MRSA) infections. The purpose of the study was to identify and characterize staphylococcal cassette chromosome mec (SCCmec) and clonal types of MRSA strains, exhibiting the vancomycin MIC creep phenomenon.
Methods:
A total of 3305 S. aureus strains were isolated from various clinical samples of Lahore General Hospital, Lahore, Pakistan. MRSA strains were identified by cefoxitin resistant (≤21mm) followed by mecA and mecC gene genotyping. Vancomycin MIC creep was determined by E-test. Isolates having MIC values >1.5 µg/mL were further subjected for SCCmec typing (I-V and XI) and multiple-locus variable number tandem repeat analysis (MLVA) by amplification of spa, sspA, clfA, clfB, and sdrCDE genes. A dendrogram was created based on the similarity index using bioneumerics software.
Results:
About 13.3% (440/3305) isolates were MRSA with 99.3% (437/440) and 0.7% (3/440) carried mecA and mecC genes, respectively. In 120 MRSA isolates, the MIC of vancomycin was >1.5µg/mL. In MRSA isolates with high vancomycin MIC (>1.5µg/mL), the most common SCCmec type was SCCmec III (38.3%), followed by SCCmec IVa (15.8%), SCCmec IIIa (13.3%,), SCCmec IVc (7.5%), SCCmec IVe (5.8%), SCCmec IVd (5.8%), SCCmec IVb (4.2%), SCCmec II (2.5%), SCCmec V (1.7%), SCCmec I (1.7%) and SCCmec XI (1.7%). MLVA revealed 60 genotypic groups of MRSA isolates having a 92% similarity index.
Conclusion:
SCCmec III was the most common type in genetically related MRSA isolates showing vancomycin MIC creep. The presence of SCCmec XI may further add burden to infection control measures.
Insights
This study identified staphylococcal cassette chromosome mec (SCCmec) and clonal types in methicillin-resistant Staphylococcus aureus (MRSA) with vancomycin minimum inhibitory concentration (MIC) creep. SCCmec III was most common in MRSA strains showing vancomycin MIC creep.
Area of Science:
- Microbiology
- Infectious Diseases
- Genetics
Background:
- Vancomycin minimum inhibitory concentration (MIC) creep is a significant concern in severe methicillin-resistant Staphylococcus aureus (MRSA) infections, correlating with treatment failure and mortality.
- Understanding the genetic characteristics of MRSA strains exhibiting this phenomenon is crucial for effective treatment strategies.
Purpose of the Study:
- To identify and characterize the staphylococcal cassette chromosome mec (SCCmec) and clonal types of MRSA strains displaying vancomycin MIC creep.
- To investigate the genetic diversity of MRSA isolates associated with increasing vancomycin MIC values.
Main Methods:
- Analysis of 3305 S. aureus strains from clinical samples, identifying MRSA via cefoxitin resistance and mecA/mecC gene detection.
- Vancomycin MIC creep determination using E-test; SCCmec typing (I-V, XI) and MLVA (using spa, sspA, clfA, clfB, sdrCDE genes) for isolates with MIC >1.5 µg/mL.
- Dendrogram creation based on similarity index using bionumerics software to analyze clonal relationships.
Main Results:
- 13.3% of isolates were MRSA, with mecA being the predominant gene (99.3%).
- Among 120 MRSA isolates with vancomycin MIC >1.5 µg/mL, SCCmec III was the most prevalent type (38.3%), followed by SCCmec IVa (15.8%).
- Multiple-locus variable number tandem repeat analysis identified 60 genotypic groups among MRSA isolates, indicating significant genetic diversity.
Conclusions:
- SCCmec III is the most common type among genetically related MRSA isolates exhibiting vancomycin MIC creep.
- The identification of SCCmec XI warrants attention for infection control due to potential implications.
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