title: A novel gene amplification causes upregulation of the PatAB ABC transporter and fluoroquinolone resistance in Streptococcus pneumoniae.
abstract: Overexpression of the ABC transporter genes patA and patB confers efflux-mediated fluoroquinolone resistance in Streptococcus pneumoniae and is also linked to pneumococcal stress responses. Although upregulation of patAB has been observed in many laboratory mutants and clinical isolates, the regulatory mechanisms controlling expression of these genes are unknown. In this study, we aimed to identify the cause of high-level constitutive overexpression of patAB in M184, a multidrug-resistant mutant of S. pneumoniae R6. Using a whole-genome transformation and sequencing approach, we identified a novel duplication of a 9.2-kb region of the M184 genome which included the patAB genes. This duplication did not affect growth and was semistable with a low segregation rate. The expression levels of patAB in M184 were much higher than those that could be fully explained by doubling of the gene dosage alone, and inactivation of the first copy of patA had no effect on multidrug resistance. Using a green fluorescent protein reporter system, increased patAB expression was ascribed to transcriptional read-through from a tRNA gene upstream of the second copy of patAB. This is the first report of a large genomic duplication causing antibiotic resistance in S. pneumoniae and also of a genomic duplication causing antibiotic resistance by a promoter switching mechanism.
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, Institute of Microbiology and Infection, and College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom.
authors.forename: Alison J
authors.initials: AJ
authors.lastname: Baylay
authors.affiliation: Centre for Immunity, Infection and Evolution, Ashworth Laboratories, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Alasdair
authors.initials: A
authors.lastname: Ivens
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, Institute of Microbiology and Infection, and College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom l.j.v.piddock@bham.ac.uk.
authors.forename: Laura J V
authors.initials: LJ
authors.lastname: Piddock
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D024841:Fluoroquinolones / Q000494:pharmacology*; D005784:Gene Amplification / Q000235:genetics*; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000235:genetics*
chemical_list: D018528:ATP-Binding Cassette Transporters; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D024841:Fluoroquinolones