Molecular genetics of polymyxin resistance in Salmonella typhimurium

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Polymyxin antibiotics are crucial for treating multidrug-resistant Gram-negative bacterial infections.
• Mechanisms of resistance, particularly to polymyxins, are of significant clinical and research interest.
• The pmrA gene is a known regulator involved in bacterial resistance pathways.

Purpose of the Study:

• To investigate the role of a newly discovered gene, pmrD, in conferring resistance to antibiotics.
• To elucidate the regulatory relationship between pmrD and the pmrAB two-component system.
• To understand the molecular basis of polymyxin resistance.

Main Methods:

• Genetic analysis of bacterial resistance mutations.
• Gene expression studies using multicopy plasmids.
• Assays to determine antibiotic resistance levels.

Main Results:

• The pmrD gene confers resistance to polymyxin B, comparable to the pmrA505 mutation.
• Strains expressing pmrD are not resistant to colistin (CAP).
• PmrD-mediated resistance to polymyxin B requires the presence of the wild-type pmrA gene.
• PmrA505 expression is suboptimal without pmrD, suggesting a functional interaction.

Conclusions:

• The pmrD gene is a novel contributor to polymyxin B resistance.
• PmrD-mediated resistance is dependent on the pmrA gene product.
• These findings suggest that pmrD is regulated by the pmrAB two-component system, providing new insights into polymyxin resistance mechanisms.