title: Rampant Parasexuality Evolves in a Hospital Pathogen during Antibiotic Selection.
abstract: Horizontal gene transfer threatens the therapeutic success of antibiotics by facilitating the rapid dissemination of resistance alleles among bacterial species. The conjugative mobile element Tn916 provides an excellent context for examining the role of adaptive parasexuality as it carries the tetracycline-resistance allele tetM and has been identified in a wide range of pathogens. We have used a combination of experimental evolution and allelic frequency measurements to gain insights into the adaptive trajectories leading to tigecycline resistance in a hospital strain of Enterococcus faecalis and predict what mechanisms of resistance are most likely to appear in the clinical setting. Here, we show that antibiotic selection led to the near fixation of adaptive alleles that simultaneously altered TetM expression and produced remarkably increased levels of Tn916 horizontal gene transfer. In the absence of drug, approximately 1 in 120,000 of the nonadapted E. faecalis S613 cells had an excised copy of Tn916, whereas nearly 1 in 50 cells had an excised copy of Tn916 upon selection for resistance resulting in a more than 1,000-fold increase in conjugation rates. We also show that tigecycline, a translation inhibitor, selected for a mutation in the ribosomal S10 protein. Our results show the first example of mutations that concurrently confer resistance to an antibiotic and lead to constitutive conjugal-transfer of the resistance allele. Selection created a highly parasexual phenotype and high frequency of Tn916 jumping demonstrating how the use of antibiotics can lead directly to the proliferation of resistance in, and potentially among, pathogens.
authors.affiliation: Department of BioSciences, Rice University.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Beabout
authors.affiliation: Department of BioSciences, Rice University.
authors.forename: Troy G
authors.initials: TG
authors.lastname: Hammerstrom
authors.affiliation: Department of BioSciences, Rice University.
authors.forename: Tim T
authors.initials: TT
authors.lastname: Wang
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston.
authors.forename: Minny
authors.initials: M
authors.lastname: Bhatty
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Christie
authors.affiliation: Department of BioSciences, Rice University.
authors.forename: Gerda
authors.initials: G
authors.lastname: Saxer
authors.affiliation: Department of BioSciences, Rice University shamoo@rice.edu.
authors.forename: Yousif
authors.initials: Y
authors.lastname: Shamoo
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000222:Adaptation, Physiological / Q000187:drug effects; D000483:Alleles; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D002876:Chromosomes, Bacterial / Q000235:genetics; D019020:Directed Molecular Evolution; D004352:Drug Resistance, Microbial / Q000187:drug effects / Q000235:genetics*; D013293:Enterococcus faecalis / Q000187:drug effects / Q000235:genetics*; D018628:Gene Dosage; D006761:Hospitals; D006801:Humans; D008911:Minocycline / Q000031:analogs & derivatives / Q000494:pharmacology; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional / Q000235:genetics; D010641:Phenotype; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism; D017384:Sequence Deletion; D000078304:Tigecycline; D016896:Treatment Outcome
chemical_list: D018528:ATP-Binding Cassette Transporters; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D000078304:Tigecycline; D008911:Minocycline
keywords: Enterococcus faecalis; antibiotic resistance; experimental evolution; horizontal gene transfer; pathogen; tigecycline