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Background: Bovine respiratory disease (BRD) is common in intensively raised cattle and is often treated with antibiotics. For practitioners, knowledge of the bacteria involved in an outbreak and their antibiotic susceptibility is warranted. To this end, samples from the upper or lower respiratory tract of calves can be submitted for bacteriological culture and susceptibility testing of relevant isolates. However, it is debated whether isolates from the upper respiratory tract are representative of bacteria causing infections in the lower respiratory tract. In this study, we used MALDI-TOF MS, multilocus sequence typing (MLST) and core-genome multilocus sequence typing (cgMLST) to compare culture results of 219 paired samples (sample pairs) of deep nasal swabs (DNS) and tracheobronchial lavage (TBL). The sample pairs came from 171 calves in 30 calf groups across 25 farms with 48 calves sampled twice. Results: The predominant bacterial pathogen was Pasteurella multocida, which was isolated from 37.4% of DNS and 22.4% of TBL. There was no statistically significant difference in isolation frequency of P. multocidabetween calves considered healthy and those suspected for BRD for DNS (P= 0.778) or TBL (P= 0.410). Among the 49 sample pairs where P. multocidawas isolated from TBL, the same species was isolated from DNS in 29 sample pairs (59.2%). Isolates from 28 of these sample pairs were evaluated by MLST, and in 24 pairs (86.0%) P. multocidafrom DNS and TBL were of the same sequence type (ST). Moreover, cgMLST showed that the genetic distance between isolates within 21 of the 28 sample pairs (75.0%), was less than two alleles, and DNS and TBL isolates were considered identical. In seven sample pairs (25%), the genetic distance was greater, and DNS and TBL isolates were considered nonidentical. Conclusions: Pasteurella multocidawas readily isolated from DNS and in calves where this species was isolated also from TBL, DNS and TBL isolates were identical in 75% of the sample pairs. This suggests that during an outbreak of BRD, submission of DNS samples from 4 to 6 calves could be a convenient approach for practitioners seeking guidance on P. multocidapresent in the lower respiratory tract and their antibiotic susceptibility.

•mcr-9is common among clinical ESBL-producing Enterobacteriaceae isolates from horses in Sweden.•mcr-9appears linked to blaSHV-12and plasmid replicon types IncHI2 and IncHI2A.•The potential regulatory genes qseB- and qseC-like for mcr-9were not detected.•Spread of mcr-9is mainly horizontal, but some clonal dissemination was observed.•All mcr-9-positive isolates carried resistance genes to all antibiotics authorised for treatment of horses in Sweden.