Abstract
Multidrug-resistant (MDR; resistance to ≥3 antimicrobial classes) members of the Pasteurellaceae family may compromise the efficacy of therapies used to prevent and treat bovine respiratory disease (BRD) in feedlot cattle. This study examined the prevalence of multidrug resistance in strains of Mannheimia haemolytica and Pasteurella multocida collected from BRD cattle mortalities in North America. Isolates of M. haemolytica (n = 147) and P. multocida (n = 70) spanning 69 Alberta feedlots from 2011 to 2016 and two United States feedlots from 2011 to 2012 were examined for antimicrobial resistance (AMR) in association with integrative and conjugative elements (ICEs). Overall, resistance was high in both bacterial species with an increase in the prevalence of MDR isolates between 2011 and 2016. Resistance to >7 antimicrobial drugs occurred in 31% of M. haemolytica and 83% of P. multocida isolates. Resistance to sulfadimethoxine, trimethoprim/sulfamethoxazole, neomycin, clindamycin oxytetracycline, spectinomycin, tylosin, tilmicosin, and tulathromycin was most common. Although >80% of strains harbored three or more ICE-associated genes, only 12% of M. haemolytica and 77% of P. multocida contained all six, reflecting the diversity of ICEs. There was evidence of clonal spread as P. multocida and M. haemolytica isolates with the same pulsed-field gel electrophoresis profile from the United States in 2011 were isolated in Alberta in 2015–2016. This work highlights that MDR strains of Pasteurellaceae containing ICEs are widespread and may be contributing to BRD therapy failure in feedlot cattle. Given the antimicrobial resistance gene profiles identified, these MDR isolates may be selected for by the use of macrolides, tetracyclines, and/or in-feed supplements containing heavy metals.
Highlights
Bovine respiratory disease (BRD) continues to be the principal health problem for beef production, contributing significantly to economic loss through mortality (1% of death loss) and morbidity (Hilton, 2014)
A trend toward higher resistance to some antimicrobials was observed over time in both P. multocida and M. haemolytica isolates, there was considerable temporal and/or geographical variation in resistance to most antimicrobials
This study suggests that between 2011 and 2016 there was a significant increase in the prevalence of MDR isolates of M. haemolytica and P. multocida associated with bovine respiratory disease (BRD)
Summary
Bovine respiratory disease (BRD) continues to be the principal health problem for beef production, contributing significantly to economic loss through mortality (1% of death loss) and morbidity (up to 80%) (Hilton, 2014). Multiple viral [bovine herpesvirus type 1 (BHV-1), parainfluenza-3 virus (PI3), bovine viral diarrhea virus (BVDV), and bovine respiratory syncytial virus (BRSV)] and bacterial agents (Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis) are implicated in BRD, resulting in a disease complex comprised of numerous forms of pneumonia with varied pathologies. These include bronchopneumonia and fibrinous pneumonia typically associated with P. multocida and M. haemolytica, respectively (Booker et al, 2008); both species are members of the Pasteurellaceae family. This selection pressure may be higher for pathogenic bacteria that are the primary targets of antimicrobial therapy, such as the BRD-associated species, as they are likely to be more frequently exposed to drugs than commensal species
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