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Some effects of plasmids coding for antibiotic resistance on the virulence of Staphylococcus aureus
Abstract:
The relative virulence of pairs of staphylococci differing in resistance plasmid content has been studied using the neonatal mouse weight gain test. Both clinical and laboratory strains were used which had undergone genetic manipulation, either curing for loss of plasmids or transduction for gain of plasmids. A difference in virulence was detected between two variants of S. aureus NCTC 8325 possessing different plasmids coding for penicillinase. However in most cases any form of genetic manipulation seemed to reduce the virulence of the staphylococcus. In the case of NCTC 9789 (PS 80) which was originally an epidemic strain, curing of a plasmid coding for cadmium resistance resulted in reduced virulence but original virulence could not be restored by transduction of the plasmid into the cured derivative.
Insights
Investigating Staphylococcus virulence, this study found that genetic manipulation, like plasmid loss or gain, often reduced bacterial virulence. While some plasmid differences affected virulence, restoring it proved challenging.
Area of Science:
- Microbiology
- Molecular Biology
- Infectious Diseases
Background:
- Staphylococci are significant pathogens, and their virulence can be influenced by genetic elements.
- Plasmids, extrachromosomal DNA in bacteria, often carry genes conferring antibiotic resistance and potentially affecting virulence factors.
Purpose of the Study:
- To investigate the impact of resistance plasmid content on the relative virulence of Staphylococcus strains.
- To understand how genetic manipulation (plasmid loss or gain) affects Staphylococcus virulence.
Main Methods:
- Utilized the neonatal mouse weight gain test to assess bacterial virulence.
- Employed genetic manipulation techniques: plasmid curing (loss) and transduction (gain) on both clinical and laboratory Staphylococcus strains.
- Compared virulence between bacterial variants with differing plasmid profiles.
Main Results:
- A difference in virulence was observed between Staphylococcus aureus NCTC 8325 variants with plasmids encoding different penicillinase types.
- In most instances, genetic manipulation, including plasmid loss or gain, led to a reduction in Staphylococcus virulence.
- For Staphylococcus NCTC 9789 (PS 80), curing a cadmium resistance plasmid decreased virulence, and subsequent transduction could not restore original virulence.
Conclusions:
- Resistance plasmids can influence Staphylococcus virulence, though the effect is not always straightforward.
- Genetic manipulation of Staphylococcus strains, particularly plasmid modification, frequently attenuates virulence.
- Restoring virulence through plasmid transduction may be complex and strain-dependent.