title: Biocide Susceptibility of Staphylococcus aureus CC398 and CC30 Isolates from Pigs and Identification of the Biocide Resistance Genes, qacG and qacC.
abstract: OBJECTIVE
  Methicillin-resistant Staphylococcus aureus (MRSA), in particular clonal complex (CC) 398, is increasingly found in livestock. Recently, MRSA CC30 was identified in Danish pigs. We determined the susceptibility of porcine S. aureus isolates of CC398 and CC30 to disinfectants used in pig farming (benzalkonium chloride, hydrogen peroxide, formaldehyde, sodium hypochlorite, and caustic soda). Furthermore, efflux pump activity, antimicrobial resistance profiles, hemolysis properties, and the presence of toxic shock syndrome toxin-1 (TSST-1) and Panton-Valentine Leukocidin (PVL)-encoding virulence factors were investigated.
  
  
  METHODS
  Susceptibilities to biocides and antimicrobial agents of 79 porcine S. aureus isolates were determined by the microdilution method. Isolates comprised 21 methicillin-sensitive S. aureus (MSSA) and 40 MRSA isolates belonging to CC398 and 13 MSSA and 5 MRSA isolates belonging to CC30. The presence of quaternary ammonium compound (QAC) resistance efflux pumps was analyzed using an ethidium bromide accumulation assay. The presence of qac resistance genes in active efflux pump positive isolates was determined by whole-genome sequencing data. All isolates were screened for lukPV and tst genes with PCR, and hemolytic activities were determined using an agar plate assay.
  
  
  RESULTS
  S. aureus isolates did not show reduced susceptibility to the biocides tested. However, the QAC resistance gene, qacG, was detected in three MRSA CC30 isolates and the qacC in one MRSA CC30 isolate. CC30 isolates were generally more susceptible to non-beta-lactam antibiotics than CC398. Isolates generally had low hemolytic activity and none encoded PVL or TSST-1.
  
  
  CONCLUSIONS
  The presence of qac genes in European porcine S. aureus isolates and in livestock-associated MRSA CC30 is for the first time described in this study. This finding is concerning as it ultimately may compromise disinfection with QACs and thereby contribute to the selection and spread of MRSA CC30.
authors.affiliation: 1 Division for Epidemiology and Microbial Genomics, National Food Institute, Technical University of Denmark , Lyngby, Denmark .
authors.forename: Maria Amalie
authors.initials: MA
authors.lastname: Seier-Petersen
authors.affiliation: 2 Department of Veterinary Disease Biology, Faculty of Health, University of Copenhagen , Copenhagen, Denmark .
authors.forename: Lene Nørby
authors.initials: LN
authors.lastname: Nielsen
authors.affiliation: 2 Department of Veterinary Disease Biology, Faculty of Health, University of Copenhagen , Copenhagen, Denmark .
authors.forename: Hanne
authors.initials: H
authors.lastname: Ingmer
authors.affiliation: 1 Division for Epidemiology and Microbial Genomics, National Food Institute, Technical University of Denmark , Lyngby, Denmark .
authors.forename: Frank Møller
authors.initials: FM
authors.lastname: Aarestrup
authors.affiliation: 1 Division for Epidemiology and Microbial Genomics, National Food Institute, Technical University of Denmark , Lyngby, Denmark .
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Agersø
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001548:Benzalkonium Compounds / Q000494:pharmacology; D004202:Disinfectants / Q000494:pharmacology*; D004912:Erythrocytes / Q000187:drug effects; D005557:Formaldehyde / Q000494:pharmacology; D015870:Gene Expression; D006461:Hemolysis / Q000187:drug effects; D059014:High-Throughput Nucleotide Sequencing; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012756:Sheep; D012973:Sodium Hypochlorite / Q000494:pharmacology; D013203:Staphylococcal Infections / Q000382:microbiology / Q000473:pathology / Q000662:veterinary*; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology* / Q000473:pathology; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001548:Benzalkonium Compounds; D004202:Disinfectants; D026901:Membrane Transport Proteins; D020033:Protein Isoforms; D000644:Quaternary Ammonium Compounds; D037521:Virulence Factors; C068498:qacA protein, Staphylococcus aureus; D005557:Formaldehyde; D012973:Sodium Hypochlorite