Oral Presentation The Prato Conference on the Pathogenesis of Bacterial Infections of Animals 2016

ICE-associated multidrug resistance in Pasteurellaceae species isolated from fatal bovine respiratory disease cases in North American feedlots  (#19)

Cassidy L. Klima 1 , Rahat Zaheer 1 , Shaun R. Cook 2 , Brenda J. Ralston 2 , Nick Allan 3 , R. Michele Anholt 4 , Andrew Cameron 1 , Yan D. Niu 2 , Kim Stanford 2 , Ron R. Read 4 , Tim A. McAllister 1
  1. Agriculture and Agri-Food Canada, Lethbridge, AB, Canada
  2. Alberta Agriculture and Forestry , Lethbridge, AB, Canada
  3. Chinook Contract Research Inc., Victoria, BC, Canada
  4. University of Calgary, Calgary, AB, Canada

Multidrug resistance (MDR) conferring integrative conjugative elements (ICEs) harboured by Mannheimia haemolytica (MH), Pasteurella multocida (PM) and Histophilus somni (HS) are a significant threat to the effective prevention and treatment of bovine respiratory disease in the North American beef industry.  Isolates of MH (133), PM (51), and HS (50) spanning 53 Alberta feedlots from 2011-2016 and two US feedlots from 2011-2012 were examined for antimicrobial resistance (AMR) in association with ICEs.  Genotyping was performed using PFGE, antimicrobial susceptibility testing completed using the Sensititre bovine/porcine panel, and PCR used to screen for six genes associated with ICEPmu1 and 11 AMR determinants.  The prevalence of MDR was high in all species with 87.4% of MH, 89.28% of PM, and 87.2% of HS resistant to at least three drugs.  Of these cases, XMDR (resistance to ≥5 drugs) occurred in 87.2% of MH, 94.1% of PM and 62% of HS. Resistance levels were greatest to oxytetracycline (91%), tilmicosin (65%) and tulathromycin (59%).  Although ˃80% of MDR strains harboured at least three ICE-associated genes, only 13% of MH, 75% of PM, and 38% of HS contained all six, indicating some diversity in the backbone of the ICEs detected. Multiple cases of clonal spread were observed, including strains of extreme MDR PM and MH isolated originally from the US in 2011 and then again from Alberta in 2015- 2016.  Similarities in ICE/AMR gene profiles indicate that in addition to clonal dissemination, AMR containing ICEs have spread independently throughout populations of MH, PM, and HS. This work highlights that AMR containing ICEs are widespread in strains of Pasteurellaceae contributing to BRD mortalities in beef cattle in North America.  These mobile elements are likely being selected for through the use of macrolides, tetracyclines and/or in-feed supplementation containing heavy metals.