title: Antimicrobial resistance genes in Actinobacillus pleuropneumoniae, Haemophilus parasuis and Pasteurella multocida isolated from Australian pigs.
abstract: OBJECTIVE
  To identify genes associated with the observed antimicrobial resistance in Actinobacillus pleuropneumoniae, Haemophilus parasuis and Pasteurella multocida isolated from Australian pigs.
  
  
  METHODS
  Isolates with known phenotypic resistance to β-lactams, macrolides and tetracycline were screened for the presence of antimicrobial resistance genes.
  
  
  METHODS
  A total of 68 A. pleuropneumoniae, 62 H. parasuis and 20 P. multocida isolates exhibiting phenotypic antimicrobial resistance (A. pleuropneumoniae and P. multocida) or elevated minimal inhibitory concentrations (MICs) (H. parasuis) to any of the following antimicrobial agents - ampicillin, erythromycin, penicillin, tetracycline, tilmicosin and tulathromycin - were screened for a total of 19 associated antimicrobial resistance genes (ARGs) by PCR.
  
  
  RESULTS
  The gene bla ROB-1 was found in all ampicillin- and penicillin-resistant isolates, but none harboured the bla TEM-1 gene. The tetB gene was found in 76% (74/97) of tetracycline-resistant isolates, 49/53 A. pleuropneumoniae, 17/30 H. parasuis and 8/14 P. multocida. One A. pleuropneumoniae isolate harboured the tetH gene, but none of the 97 isolates had tetA, tetC, tetD, tetE, tetL, tetM or tetO. A total of 92 isolates were screened for the presence of macrolide resistance genes. None was found to have ermA, ermB, ermC, erm42, mphE, mefA, msrA or msrE.
  
  
  CONCLUSIONS
  The current study has provided a genetic explanation for the resistance or elevated MIC of the majority of isolates of Australian porcine respiratory pathogens to ampicillin, penicillin and tetracycline. However, the macrolide resistance observed by phenotypic testing remains genetically unexplained and further studies are required.
authors.affiliation: The University of Queensland, School of Veterinary Science, Gatton, Queensland 4343, Australia. d.dayao@uq.edu.au.
authors.forename: Dae
authors.initials: D
authors.lastname: Dayao
authors.affiliation: The University of Queensland, School of Veterinary Science, Gatton, Queensland 4343, Australia.
authors.forename: J S
authors.initials: JS
authors.lastname: Gibson
authors.affiliation: The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, EcoSciences Precinct, QLD, Australia.
authors.forename: P J
authors.initials: PJ
authors.lastname: Blackall
authors.affiliation: The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, EcoSciences Precinct, QLD, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Turni
mesh_terms: D000189:Actinobacillus Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary; D016977:Actinobacillus pleuropneumoniae / Q000187:drug effects* / Q000235:genetics; D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D001315:Australia; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics*; D006192:Haemophilus Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary; D044137:Haemophilus parasuis / Q000187:drug effects* / Q000235:genetics; D010326:Pasteurella Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary; D016979:Pasteurella multocida / Q000187:drug effects* / Q000235:genetics; D013552:Swine / Q000382:microbiology; D013553:Swine Diseases / Q000188:drug therapy / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents
keywords: Actinobacillus pleuropneumoniae; Haemophilus parasuis; Pasteurella multocida; antimicrobial resistance genes; pigs