title: Prevalence, distribution and transfer of small β-lactamase-containing plasmids in Swedish Haemophilus influenzae.
abstract: OBJECTIVE
  The β-lactamase genes of Haemophilus influenzae are commonly positioned on large integrative and conjugative elements, but a group of blaTEM-carrying small plasmids (4000-6000 bp) with a common structural backbone have recently been characterized. In this study we investigated the epidemiological significance and potential for transfer of this group of small plasmids.
  
  
  METHODS
  We developed a two-step PCR assay to screen for and type this group of resistance plasmids in H. influenzae. A large collection of respiratory isolates (n = 2845) from south Sweden, obtained from 2009 to 2011, as well as a collection of invasive Swedish H. influenzae from 1997 to 2010 (n = 310) was screened. The distribution of plasmid types among clinical isolates was investigated using multilocus sequence typing (MLST).
  
  
  RESULTS
  In the collection, 15.8% of β-lactamase-producing isolates and 1.4% of total isolates possessed a small plasmid with the signature structure. The plasmids were genetically conserved and widely spread geographically. MLST revealed that the spread of small plasmids occurred by both clonal expansion and horizontal transfer. In vitro experiments suggested that one plasmid type, pN223, can transfer ampicillin resistance to susceptible Escherichia coli.
  
  
  CONCLUSIONS
  Small β-lactamase-encoding plasmids constitute a significant mechanism for β-lactam resistance in H. influenzae and can spread through clonal expansion of resistant clones as well as through horizontal plasmid transfer.
authors.affiliation: Medical Microbiology, Department of Laboratory Medicine, Lund University, Malmö, Sweden.
authors.forename: Christophe
authors.initials: C
authors.lastname: Fleury
authors.forename: Fredrik
authors.initials: F
authors.lastname: Resman
authors.forename: Josephine
authors.initials: J
authors.lastname: Rau
authors.forename: Kristian
authors.initials: K
authors.lastname: Riesbeck
mesh_terms: D000328:Adult; D002648:Child; D002675:Child, Preschool; D004269:DNA, Bacterial / Q000235:genetics; D006192:Haemophilus Infections / Q000382:microbiology*; D006193:Haemophilus influenzae / Q000201:enzymology* / Q000235:genetics* / Q000302:isolation & purification; D006801:Humans; D058885:Multilocus Sequence Typing; D010957:Plasmids / Q000032:analysis*; D016133:Polymerase Chain Reaction; D015995:Prevalence; D013548:Sweden; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D004269:DNA, Bacterial; D001618:beta-Lactamases
keywords: antimicrobial resistance; clinical epidemiology; horizontal gene transfer; phylogenetic analysis