biostudies-literatureUnknown9Hirsch C<h4>Introduction</h4>Bacterial bronchopneumonia (BP) has been associated with purchasing cattle through auction markets. However, whether auction markets are a source of BP-associated bacterial pathogens is unknown. This study evaluated prevalence, antimicrobial susceptibility, and genetic relatedness (using pulsed-field gel electrophoresis, PFGE) of <i>Mannheimia haemolytica, Pasteurella multocida</i>, and <i>Histophilus somni</i> isolated from cattle either transported to an auction market prior to feedlot placement (AUC), or directly to a feedlot from a farm (RANC).<h4>Methods</h4>Two groups of cattle were enrolled (N = 30 per group) from two separate farms with 15 animals from an individual farm designated as AUC or RANC. Deep nasal swab (DNS) and trans-tracheal aspirates (TTA) were collected on day 0 at weaning (T0) and on day 2 at on-arrival processing at the feedlot (T1). The DNS were also collected on day 9 (T2) and day 30 (T3) after arrival at the feedlot.<h4>Results and discussion</h4>In both TTA and DNS, prevalence of bacteria did not differ between AUC and RANC groups (<i>P</i> > 0.05). None of the bacteria isolated at T0 were resistant to antimicrobials and diversity of all bacteria was greatest at T0 and T1. In Group 1 cattle, 100% of <i>P. multocida</i> isolated at T2 and T3 were multi-drug resistant. These isolates were highly related (>90%) according to PFGE, with most being clones. Though limited in size, results for animals evaluated in this study suggested that auction markets were not a major source of resistant BP pathogens, however, horizontal transmission of a multi-resistant strain of <i>P. multocida</i> occurred in a feedlot. Spread of resistant <i>P. multocida</i> was likely due to the selective pressures imposed by feedlot antimicrobial use and encoded resistance by the bacteria.Frontiers in veterinary science1026470https://www.ebi.ac.uk/biostudies/studies/S-EPMC9902877biostudies-literatureComparison of pathogenic bacteria in the upper and lower respiratory tracts of cattle either directly transported to a feedlot or co-mingled at auction markets prior to feedlot placement.PMC9902877Hirsch CAlexander TWTimsit EUddin MSGuan LLfalseComparison of pathogenic bacteria in the upper and lower respiratory tracts of cattle either directly transported to a feedlot or co-mingled at auction markets prior to feedlot placement.<h4>Introduction</h4>Bacterial bronchopneumonia (BP) has been associated with purchasing cattle through auction markets. However, whether auction markets are a source of BP-associated bacterial pathogens is unknown. This study evaluated prevalence, antimicrobial susceptibility, and genetic relatedness (using pulsed-field gel electrophoresis, PFGE) of <i>Mannheimia haemolytica, Pasteurella multocida</i>, and <i>Histophilus somni</i> isolated from cattle either transported to an auction market prior to feedlot placement (AUC), or directly to a feedlot from a farm (RANC).<h4>Methods</h4>Two groups of cattle were enrolled (N = 30 per group) from two separate farms with 15 animals from an individual farm designated as AUC or RANC. Deep nasal swab (DNS) and trans-tracheal aspirates (TTA) were collected on day 0 at weaning (T0) and on day 2 at on-arrival processing at the feedlot (T1). The DNS were also collected on day 9 (T2) and day 30 (T3) after arrival at the feedlot.<h4>Results and discussion</h4>In both TTA and DNS, prevalence of bacteria did not differ between AUC and RANC groups (<i>P</i> > 0.05). None of the bacteria isolated at T0 were resistant to antimicrobials and diversity of all bacteria was greatest at T0 and T1. In Group 1 cattle, 100% of <i>P. multocida</i> isolated at T2 and T3 were multi-drug resistant. These isolates were highly related (>90%) according to PFGE, with most being clones. Though limited in size, results for animals evaluated in this study suggested that auction markets were not a major source of resistant BP pathogens, however, horizontal transmission of a multi-resistant strain of <i>P. multocida</i> occurred in a feedlot. Spread of resistant <i>P. multocida</i> was likely due to the selective pressures imposed by feedlot antimicrobial use and encoded resistance by the bacteria.2022-01-01T00:00:00Z20222025-04-04T18:43:47.139Z2025-04-04T18:43:47.139ZS-EPMC99028773676140210.3389/fvets.2022.1026470