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Updated: Feb 24, 2026
Quantification of Plasmid-Mediated Antibiotic Resistance in an Experimental Evolution Approach
Published on: December 14, 2019
Multiple plasmid interference - Pledging allegiance to my enemy's enemy
João Alves Gama1, Rita Zilhão2, Francisco Dionisio3
1cE3c-Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal; Instituto Gulbenkian de Ciência, Oeiras, Portugal.
Abstract:
As shown in the previous article, two distinct conjugative plasmids sometimes interact within bacterial cells, implicating changes of transfer rates. In most cases of interactions within bacteria, the transfer of one of the plasmids decreases. Less frequently, the transfer rate of one of the plasmids increases. Here we analyse what happens if three distinct conjugative plasmids colonize the same bacterial cell. Our aim is to understand how interactions between two plasmids affect the transfer rate of the third plasmid. After showing that plasmids interact in 59 out of 84 possible interactions we show that, with some exceptions, if the transfer rate of a plasmid decreases in the presence of a second plasmid, a decrease is also observed in the presence of a third plasmid. Moreover, if the conjugation rate of a plasmid increases in the presence of another, an increase is also observed if there is a third plasmid in the cell. Both types of interactions are mostly independent of the third plasmid's identity, even if sometimes the third plasmid quantitatively distorts the interaction of the other two plasmids. There is a bias towards negative intensifying interactions, which provide good news concerning the spread conjugative plasmids encoding antibiotic-resistance genes and virulence factors.
Insights
Interactions between three conjugative plasmids in bacteria show predictable transfer rate changes. If one plasmid hinders another, a third plasmid often has a similar effect, suggesting limited impact from the third plasmid
Area of Science:
- Bacterial genetics
- Molecular biology
- Microbiology
Background:
- Conjugative plasmids can interact within bacterial cells, altering their transfer rates.
- Previous studies documented interactions between two conjugative plasmids, showing either decreased or increased transfer rates.
Purpose of the Study:
- To investigate the interactions among three distinct conjugative plasmids within the same bacterial cell.
- To determine how interactions between two plasmids influence the transfer rate of a third plasmid.
Main Methods:
- Analyzing the transfer rates of conjugative plasmids in bacterial cells containing multiple plasmids.
- Quantifying plasmid interactions across various combinations of three distinct conjugative plasmids.
Main Results:
- Plasmids interact in a significant majority (59/84) of combinations.
- Interactions are largely consistent: if plasmid A decreases plasmid B's transfer rate, plasmid C often does too.
- The effect of a third plasmid is generally independent of its identity, though it can quantitatively modulate existing interactions.
Conclusions:
- Conjugative plasmid interactions in multi-plasmid bacterial systems exhibit predictable patterns.
- The presence of a third plasmid typically reinforces the interaction dynamics established by two plasmids.
- A bias towards negative interactions (decreased transfer rates) has positive implications for controlling the spread of antibiotic resistance and virulence factors.
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