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Research Summary - 2

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

Date/Time: 9/13/2019    8:30
Author: Edouard  Timsit
Clinic: Faculty of Veterinary Medicine, University of Calgary
City, State, ZIP: Calgary, AB  T2N1N4

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

E. Timsit, DVM, PhD, DECBHM ; T.W. Alexander, PhD ;
1Department of Production Animal Health, Simpson Ranch Chair in Cattle Health and Wellness, Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada
2Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada

Introduction:

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 one 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).

Materials and Methods:

Newly-received beef-crossed feedlot calves (arrival body-weight ± SD = 282 ± 28 kg) with BRD (n = 210) and pen-matched controls (n = 107) were sampled by DNS and TTA at 4 feedlots in Western Canada. M. haemolytica, P. multocida and H. somni were isolated from DNS and TTA samples and their AMR profiles were determined using broth dilution method. Isolates were then typed by PFGE and grouped into pulsotypes (≥90% similarity).

Results:

In total, 195, 277 and 139 isolates of M. haemolytica, P. multocida and H. somni, respectively, were isolated from DNS and TTA samples. A high proportion of M. haemolytica (≥ 73%) and P. multocida (≥ 78%) isolated from DNS and TTA were resistant against oxytetracycline (OXY) and tulathromycin (TUL). Concerning H. somni, there were high levels of resistance against OXY (≥ 52%) and penicillin (PEN; ≥52%) in both DNS and TTA samples. None or few isolates were resistant to florfenicol (FEE), enrofloxacin (ENR) and ceftiofur (CEF). M. haemolytica isolates were distributed among 20 pulsotypes and 26 singlets. However, the majority of isolates (54%) belonged to a single pulsotype, which displayed resistance to TUL and OXY. This pulsotype was isolated from 29 different pens across all 4 feedlots. P. multocida isolates were distributed among 9 pulsotypes and 11 singlets with the majority of isolates (67%) belonging to one pulsotype that displayed resistance to TUL and OXY. This pulsotype was present in 33 pens across all 4 feedlots. H. somni isolates were distributed among 13 pulsotypes and 28 singlets that were either susceptible to all antimicrobials tested or resistant to PEN and OXY.

Significance:

The genotyping and antimicrobial susceptibility testing of Pasteurellaceae isolated from cattle recently placed at 4 feedlots showed that MDR clones of M. haemolytica and P. multocida can be shared among a large number of cattle within and between feedlots. As cattle were very likely from multiple origins, this finding suggests a horizontal transmission of these clones among cattle shortly after arrival at the feedlots.


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