title: Co-transfer of resistance to high concentrations of copper and first-line antibiotics among Enterococcus from different origins (humans, animals, the environment and foods) and clonal lineages.
abstract: OBJECTIVE
  We studied the occurrence of diverse copper (Cu) tolerance genes from Gram-positive bacteria and their co-transfer with antibiotic resistance genes among Enterococcus from diverse sources.
  
  
  METHODS
  Enterococcus (n = 922) of several species and from human, animal, environment and food samples were included. Antimicrobial and CuSO4 susceptibility and conjugation assays were performed by standard procedures, bacterial screening of Cu and antibiotic resistance genes by PCR, and clonality by PFGE/multilocus sequence typing.
  
  
  RESULTS
  tcrB and cueO genes occurred in 15% (n = 137/922) and 14% (n = 128/922) of isolates, respectively, with the highest occurrence in piggeries (P < 0.05). They were more frequent among Enterococcus faecium (tcrB: 23% versus 8% in Enterococcus faecalis and 12% in other species; cueO: 25% versus 5% and 9%, respectively; P < 0.05). A correlation between phenotypic and genotypic assays was observed for most E. faecium (CuSO4 MIC50 = 24 mM in tcrB/cueO(+) versus CuSO4 MIC50 = 12 mM in tcrB/cueO(-)), but not for other species. Co-transfer of Cu tolerance (associated with tcrB, cueO or an unknown mechanism) with erythromycin, tetracycline, vancomycin, aminoglycosides or ampicillin resistance was demonstrated. A variety of PFGE types was detected among isolates carrying Cu tolerance mechanisms, some identified in sequence types (STs) often linked to human infections (E. faecium from ST18 and ST78 clonal lineages and E. faecalis clonal complex 2).
  
  
  CONCLUSIONS
  Cu tolerance might contribute to the selection/maintenance of multidrug-resistant Enterococcus (including resistance to first-line antibiotics used to treat enterococcal infections) due to the use of Cu compounds (e.g. antiseptics/animal feed supplements). The distribution of the multicopper oxidase cueO and the co-transfer of ampicillin resistance along with Cu tolerance genes are described for the first time.
authors.affiliation: REQUIMTE, Laboratório de Microbiologia, Faculdade de Farmácia, Universidade do Porto, Porto, Portugal.
authors.forename: Eduarda
authors.initials: E
authors.lastname: Silveira
authors.forename: Ana R
authors.initials: AR
authors.lastname: Freitas
authors.forename: Patrícia
authors.initials: P
authors.lastname: Antunes
authors.forename: Mariana
authors.initials: M
authors.lastname: Barros
authors.forename: Joana
authors.initials: J
authors.lastname: Campos
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Coque
authors.forename: Luísa
authors.initials: L
authors.lastname: Peixe
authors.forename: Carla
authors.initials: C
authors.lastname: Novais
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003227:Conjugation, Genetic; D003300:Copper / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D016983:Enterococcus / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D004783:Environmental Microbiology; D005516:Food Microbiology; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology* / Q000662:veterinary; D006801:Humans; D058885:Multilocus Sequence Typing; D016133:Polymerase Chain Reaction
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D003300:Copper
keywords: biocides; horizontal transfer; metals; multicopper oxidase; tcrB