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Published on: January 8, 2014
Expressional Pattern of psm-mec System in Methicillin-Resistant Staphylococcus aureus Under Oxacillin Stress
Deepshikha Bhowmik1, Shiela Chetri1, Piyush Pandey1
1Department of Microbiology, Assam University, Silchar, Assam, India.
Abstract:
The psm-mec element and other regulatory factors such as sarA, agrA, and RNAIII are responsible for maintaining the genetic framework for enhanced virulence of MRSA. psm-mec is found predominantly in the staphylococcal cassette chromosome (SCCmec). sarA, agrA, and RNAIII control gene expression to facilitate adaptation in certain environment. Genome-wide approaches have shown that expression of virulence factors is frequently regulated at transcriptional, translational level, and mRNA degradation level. In this study, transcriptional responses of psm-mec gene in accordance with other regulatory factors sarA, agrA, and RNAIII were observed under normal conditions as well as when exposed to 2 μg/ml and 6 μg/ml of oxacillin stress. One-way t-test was carried out for analysing RQ values obtained through real-time PCR. This study showed downregulation of psm-mec gene and upregulation of other regulatory genes at lower concentration of oxacillin. However, this was reverse when exposed against higher concentration of oxacillin. It was observed from the study that the expression of virulence factors were dependent on each other under different concentration of oxacillin. Thus, this study highlights that psm-mec, sarA, agrA, and RNAIII gene are under direct control of antibiotic pressure in a concentration-dependent manner.
Insights
The study reveals that the psm-mec gene and regulatory factors sarA, agrA, and RNAIII in MRSA are concentration-dependently controlled by oxacillin antibiotic pressure, impacting virulence factor expression.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) virulence is regulated by factors including psm-mec, sarA, agrA, and RNAIII.
- Gene expression in bacteria is controlled at multiple levels: transcriptional, translational, and mRNA degradation.
- The staphylococcal cassette chromosome (SCCmec) is a key genetic element in MRSA, often carrying virulence genes like psm-mec.
Purpose of the Study:
- To investigate the transcriptional responses of the psm-mec gene and regulatory factors (sarA, agrA, RNAIII) in MRSA.
- To determine how oxacillin antibiotic stress influences the expression of these key virulence-associated genes.
- To understand the interdependency of these genes under varying antibiotic concentrations.
Main Methods:
- Real-time PCR was used to quantify the transcriptional levels of psm-mec, sarA, agrA, and RNAIII.
- MRSA strains were exposed to different concentrations of oxacillin (2 μg/ml and 6 μg/ml) and normal conditions.
- One-way t-tests were performed to analyze the relative quantities (RQ) of gene expression.
Main Results:
- At lower oxacillin concentrations (2 μg/ml), psm-mec showed downregulation, while sarA, agrA, and RNAIII were upregulated.
- At higher oxacillin concentrations (6 μg/ml), the expression pattern reversed, with psm-mec upregulated and regulatory genes downregulated.
- The expression of virulence factors was found to be interdependent and varied with oxacillin concentration.
Conclusions:
- The expression of psm-mec, sarA, agrA, and RNAIII genes in MRSA is directly influenced by oxacillin antibiotic pressure.
- This regulation occurs in a concentration-dependent manner, highlighting the dynamic response of MRSA virulence to antibiotics.
- Understanding these regulatory mechanisms is crucial for developing strategies against MRSA infections.
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