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Updated: May 26, 2025
Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Mec-A Positive Methicillin-Susceptible Staphylococcus Aureus as a Public Health Concern: A Case Series
Sri Amelia1, Rozaimah Zain-Hamid2, Lia Kusumawati1,3
1Department of Microbiology, Faculty of Medicine, Universitas Sumatera Utara, Medan, Indonesia.
Background:
Staphylococcus aureus, an opportunistic microorganism, is the leading cause of severe bloodstream infections, including sepsis and endocarditis, which can be life-threatening. Therefore, S. aureus infection poses a significant public health challenge, particularly in developing nations. mec-a is a genetic element commonly found in Methicillin-resistant Staphylococcus aureus (MRSA) strains that characterises the S. aureus resistance phenotype.
Methods:
Clinical infection samples obtained from blood were collected and categorised as MRSA or Methicillin-sensitive Staphylococcus aureus (MSSA) using the VITEK-2 compact device. Subsequently, specific samples were gathered as case series owing to their unique characteristics. Resistance genes were detected using conventional polymerase chain reaction (PCR), followed by visualisation through electrophoresis.
Results:
Our findings were based on the identification of five instances of MSSA among samples obtained from a tertiary hospital's microbiology laboratory. Using the VITEK-2 antimicrobial susceptibility profile, these cases were determined to be MSSA. Subsequently, we conducted PCR, which revealed the presence of a mec-a-positive strain. Upon re-examination using Mueller-Hinton agar, the five strains were confirmed to be MSSA. Further analysis demonstrated that all strains were positive for Panton-Valentine leucocidin (pvl) and exfoliative toxin A (eta) gens.
Conclusions:
The positive mec-A MSSA results should serve as a warning to clinicians that a resistant strain is forthcoming. mec-A continues to be the benchmark for confirming the resistance phenotype. Additional research is essential to explore this strain.
Insights
Methicillin-sensitive Staphylococcus aureus (MSSA) strains were found to be positive for the mec-a gene, indicating a potential for future resistance. This discovery highlights the need for vigilance against emerging Staphylococcus aureus resistance patterns.
Area of Science:
- Microbiology
- Infectious Diseases
- Molecular Biology
Background:
- Staphylococcus aureus is a major cause of life-threatening bloodstream infections.
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat.
- The mec-a gene is a key indicator of methicillin resistance in S. aureus.
Purpose of the Study:
- To investigate unusual findings of mec-a gene presence in Methicillin-sensitive Staphylococcus aureus (MSSA) strains.
- To characterize the resistance and virulence factors of these unique strains.
- To alert clinicians to potential shifts in antimicrobial resistance.
Main Methods:
- Blood samples were collected and categorized as MRSA or MSSA using the VITEK-2 compact device.
- Conventional polymerase chain reaction (PCR) was used to detect resistance genes.
- Electrophoresis was employed for gene visualization.
Main Results:
- Five MSSA strains were identified from a tertiary hospital laboratory.
- PCR confirmed the presence of the mec-a gene in these MSSA strains.
- All five strains tested positive for Panton-Valentine leucocidin (pvl) and exfoliative toxin A (eta) genes.
Conclusions:
- The detection of mec-a positive MSSA strains serves as an early warning for impending resistance.
- The mec-a gene remains a critical marker for confirming resistance phenotypes.
- Further research is necessary to fully understand these emerging strains and their implications.
