Multicopy plasmids potentiate the evolution of antibiotic resistance in bacteria

Abstract

Plasmids are thought to play a key role in bacterial evolution by acting as vehicles for horizontal gene transfer, but the role of plasmids as catalysts of gene evolution remains unexplored. We challenged populations of Escherichia coli carrying the bla β-lactamase gene on either the chromosome or a multicopy plasmid (19 copies per cell) with increasing concentrations of ceftazidime. The plasmid accelerated resistance evolution by increasing the rate of appearance of novel TEM-1 mutations, thereby conferring resistance to ceftazidime, and then by amplifying the effect of TEM-1 mutations due to the increased gene dosage. Crucially, this dual effect was necessary and sufficient for the evolution of clinically relevant levels of resistance. Subsequent evolution occurred by mutations in a regulatory RNA that increased the plasmid copy number, resulting in marginal gains in ceftazidime resistance. These results uncover a role for multicopy plasmids as catalysts for the evolution of antibiotic resistance in bacteria.

A Naturally Occurring Single Nucleotide Polymorphism in a Multicopy Plasmid Produces a Reversible Increase in Antibiotic Resistance

“…However, in the absence of antibiotics, an increase in the PCN usually produces an increase in the fitness cost produced by a plasmid (10,15). To analyze this possibility we determined the biological cost of the different plasmid alleles alone and cohabiting using the coefficient of selection (s) as previously described (11).…”

“…Single mutations can give rise to new compatible plasmids that are able to coexist in the same cell, increasing the global PCN (7,8). These mutations have been widely described in vitro (9) and arise naturally by chance due to the high plasmid copy number exhibited by ColE1-like plasmids (10), but to the best of our knowledge, there are no natural examples of cohabiting ColE1 plasmids differentiated by only a single nucleotide polymorphism (SNP).…”

Hotspot mutations and ColE1 plasmids contribute to the fitness of Salmonella Heidelberg in poultry litter

“…This result supports other studies showing that the deletion of iterons increased plasmid copy number of theta plasmids (reviewed in [89, 90]). For example, Millan et al [91] showed that mutations acquired in the OriV of a synthetic ColE1-like plasmid (pBGT) carrying bla TEM-1 β-lactamase gene increased plasmid copy number and subsequently increased ceftazidime resistance several folds.…”

Fitness Costs of Plasmids: a Limit to Plasmid Transmission

“…Plasmids are widely distributed across prokaryotes, and help bacteria adapt to a myriad of different environments, conditions, and stresses (3,4), playing a key role in bacterial ecology and evolution (5)(6)(7). The most vivid testimony to the power of plasmids as catalysts for bacterial adaptation is their role in the spread of antibiotic resistance among clinical pathogens (8), which has emerged as a major health problem over the past decades (9).…”