A brief antibiotic exposure leaves plasmids persisting in bacterial communities
Antibiotic exposure can remove bacteria without plasmids and leave the remaining community slow to lose those genetic structures afterward. A peer-reviewed laboratory study identifies a delay before plasmid-free competitors reappear, followed by faster decline. Experiments and models track this ecological memory over days to weeks. They investigate resistance persistence in defined bacterial communities, without testing a treatment protocol in patients.
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Plasmid loss slows before competition speeds it up
A brief antibiotic exposure can leave plasmid-bearing bacteria dominant even after the antibiotic is removed. Resistance genes can be carried on plasmids, genetic structures with a replication process separate from the chromosome’s. In a single peer-reviewed laboratory study, the cost of carrying them was insufficient for an immediate, rapid loss. Plasmid-free competitors first had to reappear through losses during cell division. A long plateau preceded faster decline once enough competitors existed to benefit from their growth advantage.[1]
Five plasmids test the delay in different communities
Two Escherichia coli host backgrounds were used to test 5 plasmids. Of these, 2 could transfer between cells; the other 3 were fluorescently marked and nonmobilizable. They also examined synthetic communities and multispecies communities from hospital sinks. Mathematical models and simulations were compared with changes in the fraction of plasmid-bearing cells. The framework separates cell growth, genetic transfer and losses during division. Persistence lasted days to weeks in this framework, without relying solely on fast horizontal transfer or a small cost to the host.[1]
Compounds intended to remove plasmids accelerated their decline in laboratory tests. Repeated antibiotic selection can instead restore the advantage of plasmid-bearing cells before the declining phase finishes. Mutations that reduce the cost of carrying a plasmid remain another possible contributor; ecological starting conditions provide a distinct mechanism. The experiments track defined bacterial communities over time. They do not test a clinical treatment protocol or establish that the same effect sizes apply to infections in patients.[1]
