title: Antimicrobial resistance and virulence gene profiles in multi-drug resistant enterotoxigenic Escherichia coli isolated from pigs with post-weaning diarrhoea.
abstract: This study aimed to characterize antimicrobial resistance and virulence genes in multi-drug resistant enterotoxigenic Escherichia coli (ETEC) isolates (n=117) collected from porcine post-weaning diarrhoea cases in Australia (1999-2005). Isolates were serotyped, antibiogram-phenotyped for 12 antimicrobial agents and genotyped by PCR for 30 plasmid-mediated antimicrobial resistance genes (ARGs), 22 intestinal and 38 extraintestinal E. coli virulence genes (VGs). Nine serogroups were identified, the most prevalent being O149 (46.2%), O141 (11.2%) and Ont (31.6%). None of the isolates showed resistance to ceftiofur or enrofloxacin and 9.4% were resistant to florfenicol. No corresponding extended-spectrum/AmpC β-lactamase, fluoroquinolone or floR ARGs were detected. An antimicrobial resistance index (ARI) was calculated from the combined data with a weighting for each antimicrobial agent dependent upon its significance to human health. Serogroup O141 isolates had a significantly higher ARI due to an elevated prevalence of aminoglycoside ARGs and possession of more virulence genes (VGs), including ExPEC or EHEC adhesins (bmaE, sfa/focDE, fimH, ihA) in toxin-producing strains that lacked the normally associated F4 and F18 fimbriae. Few associations between ARGs and VGs were apparent, apart from tetC, sfa/focDE and ompT which, for a sub-set of O141 isolates, suggest possible plasmid acquisition from ExPEC. The multi-drug resistant ETEC ARG/VG profiles indicate a high probability of considerable strain and plasmid diversity, reflecting various selection pressures at the individual farm level rather than emergence and lateral spread of MDR resistant/virulent clones.
authors.affiliation: School of Veterinary Science, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. m.smith9@uq.edu.au
authors.forename: M G
authors.initials: MG
authors.lastname: Smith
authors.forename: D
authors.initials: D
authors.lastname: Jordan
authors.forename: T A
authors.initials: TA
authors.lastname: Chapman
authors.forename: J J-C
authors.initials: JJ
authors.lastname: Chin
authors.forename: M D
authors.initials: MD
authors.lastname: Barton
authors.forename: T N
authors.initials: TN
authors.lastname: Do
authors.forename: V A
authors.initials: VA
authors.lastname: Fahy
authors.forename: J M
authors.initials: JM
authors.lastname: Fairbrother
authors.forename: D J
authors.initials: DJ
authors.lastname: Trott
mesh_terms: D000818:Animals; D001315:Australia / Q000453:epidemiology; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D003967:Diarrhea / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D054307:Enterotoxigenic Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification* / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D016133:Polymerase Chain Reaction / Q000662:veterinary; D017422:Sequence Analysis, DNA; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology / Q000382:microbiology*; D014774:Virulence / Q000235:genetics
chemical_list: D004269:DNA, Bacterial