Cadmium-resistance plasmid in Staphylococcus lugdunensis

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Plasmids are extrachromosomal DNA elements that can carry genes conferring antibiotic resistance.
• Staphylococcus lugdunensis is a species of bacteria found in clinical settings.
• Cadmium is a heavy metal that can be toxic to bacteria.

Purpose of the Study:

• To investigate the prevalence and genetic basis of cadmium resistance in Staphylococcus lugdunensis.
• To determine if cadmium resistance in S. lugdunensis is plasmid-mediated.
• To compare the genetic elements responsible for cadmium resistance with known resistance mechanisms in other Staphylococcus species.

Main Methods:

• Isolation and characterization of cadmium-resistant Staphylococcus lugdunensis strains from clinical specimens.
• Plasmid curing experiments to assess the role of plasmids in cadmium resistance.
• Restriction endonuclease digestion and Southern-blot hybridization using a cadB gene probe.

Main Results:

• Eighteen out of 30 S. lugdunensis strains exhibited high-level cadmium resistance (MIC ≥ 125 µM).
• Cadmium sensitivity was restored in strains cured of their plasmids, indicating plasmid-mediated resistance.
• Restriction analysis revealed similarities between a cadmium resistance plasmid (pLUG10) and a known S. aureus cadmium resistance plasmid (pOX6).
• Southern-blot hybridization confirmed the presence of a cadB homologous gene on plasmids of varying sizes (2.9, 3.2, and 3.7 kb) in resistant S. lugdunensis isolates.

Conclusions:

• Cadmium resistance in a significant proportion of clinical Staphylococcus lugdunensis isolates is mediated by plasmids.
• The findings suggest that the cadmium resistance mechanism in these S. lugdunensis strains involves a gene homologous to the cadB gene of Staphylococcus aureus.
• This implies horizontal gene transfer or a shared evolutionary origin for cadmium resistance genes in staphylococci.