Genotyping and antimicrobial resistance patterns of Mannheimia haemolytica, Pasteurella multocida and Histophilus somni isolated from the upper and lower respiratory tract of feedlot cattle

Abstract

In the last 10 years, the prevalence of Pasteurellaceae resistant against drugs typically used for bronchopneumonia (BP) control has increased in feedlot cattle. Surprisingly, it is not clear whether this increase in the prevalence of multidrug resistant (MDR) bacteria is due to the spread of 1 or few multiple MDR clones among cattle during the feeding period (i.e. horizontal spread) or due to the recrudescence of MDR clones already present in the respiratory tract of cattle upon arrival at feedlots. Recently, we reported a high prevalence of MDR M. haemolytica, P. multocida, and H. somni isolated from cattle with BP in 4 feedlots in Western Canada. Unfortunately, as we did not genotype these isolates, it was not possible to determine whether a few or a large number of MDR clones were present in these feedlots, supporting either a horizontal spread of MDR clones among cattle or a recrudescence from carriers. Therefore, the objective was to genotype M. haemolytica, P. multocida, and H. somni isolates using pulsed field gel electrophoresis (PFGE).