Genetic relatedness and antimicrobial resistance in respiratory bacteria from beef calves sampled from spring processing to 40 days after feedlot entry

Publication date: Available online 27 October 2019Source: Veterinary MicrobiologyAuthor(s): Yongmei Guo, Christopher McMullen, Edouard Timsit, Jennyka Hallewell, Karin Orsel, Frank van der Meer, Sumei Yan, Trevor W. AlexanderAbstractRecent studies have shown an increase in antimicrobial-resistant bovine respiratory disease (BRD) pathogens. To investigate the origin of antimicrobial resistance in the respiratory microbiota of beef cattle, three groups (A, B, or C) of 40 calves sourced from different calf-ranches were sampled by deep nasopharyngeal swab (DNS) at the time of first on-ranch vaccination (Time point 1, T1), feedlot entry (Time point 2, T2), and 40 days after feedlot entry (Time point 3, T3; feedlots differed by group). Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni were isolated from DNS samples, tested for antimicrobial susceptibility, and subtyped by pulsed-field gel electrophoresis (PFGE). Antimicrobial resistance genes [tet(H), tet(W), and sul2] were also quantified in DNS metagenomic DNA using PCR. Prevalence of calves positive for BRD pathogens differed among groups and time-points but P. multocida was the most prevalent (61% of calves positive, at least, at one timepoint), followed by M. haemolytica (48%) and H. somni (26%). Most M. haemolytica were susceptible to all antimicrobials (88.6%; n = 70). For P. multocida, the dominant resistance phenotype was against oxytetracycline and neomycin (35.8%). Resistant P. multocida isolates w...
Source: Veterinary Microbiology - Category: Veterinary Research Source Type: research