title: The influence of nonconjugative Escherichia coli plasmids on biofilm formation and resistance.
abstract: OBJECTIVE
  This work describes the effects of the presence of nonconjugative plasmids in Escherichia coli cells forming biofilms on a flow cell system under turbulent conditions.
  
  
  RESULTS
  The pET28 and pUC8 plasmids were separately used to transform E. coli JM109(DE3). Biofilm formation, removal and antimicrobial susceptibility to the cationic biocide benzyldimethyldodecylammonium chloride (BDMDAC) were assessed. Transformed cells formed thicker biofilms with higher cell densities, and the metabolic activity was higher whereas nontransformed cells had higher viabilities. Biocide treatment was not efficient for biofilm removal but was effective for cell killing. Biofilms formed by nontransformed cells were less affected by the treatment.
  
  
  CONCLUSIONS
  Cell transformation with the tested plasmids has significant impacts on biofilm formation, cell viability, metabolic activity and resistance to biocide treatment. Our results show that in biofilm studies involving deletion/complementation experiments, a control with the strain carrying a plasmid devoid of the gene under investigation must be included so that the real effects of the genetic manipulation are not biased by the presence of the plasmid backbone.
  
  
  CONCLUSIONS
  This is the first report where the presence of nonconjugative plasmids is assessed in flow conditions analysing biofilm formation, removal and antimicrobial susceptibility of high cell-density biofilms.
authors.affiliation: LEPAE-Department of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal.
authors.forename: J S
authors.initials: JS
authors.lastname: Teodósio
authors.forename: M
authors.initials: M
authors.lastname: Simões
authors.forename: F J
authors.initials: FJ
authors.lastname: Mergulhão
mesh_terms: D001548:Benzalkonium Compounds / Q000494:pharmacology; D018441:Biofilms / Q000187:drug effects*; D004202:Disinfectants / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D010957:Plasmids / Q000235:genetics*; D014169:Transformation, Bacterial
chemical_list: D001548:Benzalkonium Compounds; D004202:Disinfectants; C005883:zephiramine