title: Genetic characterization and antimicrobial susceptibility of Mannheimia haemolytica isolated from the nasopharynx of feedlot cattle.
abstract: A surveillance study was undertaken to examine the population dynamics and antimicrobial resistance of Mannheimia haemolytica isolated from feedlot cattle. A total of 416 isolates were collected from the nasopharynx either upon entry or exit from two feedlots in southern Alberta, Canada. Isolates were serotyped, characterized by pulsed-field gel electrophoresis and tested for susceptibility to ten antimicrobial agents via disk diffusion. Resistant isolates were screened by PCR for select antimicrobial-resistance gene determinants. Isolates were highly diverse, with 335 unique pulsed-field profiles identified among 147 strongly related clusters (similarity ≥ 85%). Clonal spread of isolates throughout the feedlots was limited and no clear association was found between genetic relatedness of M. haemolytica and sampling event (entry or exit). Pulsed-field profiles sharing a common serotype and resistance phenotype tended to cluster together. The majority of isolates were identified as serotype 2 (74.5%) although both serotype 1 (11.9%) and 6 (12.7%) were detected. Only 9.54% of isolates exhibited antimicrobial resistance. Resistance to oxytetracycline was most prevalent (n=16), followed by ampicillin (n=10), and amoxicillin/clavulanic acid (n=7). Multi-drug resistance was observed in five isolates. The tetH gene was detected in all but two oxytetracycline resistant isolates. Other detectable resistance determinates included ermX and bla(ROB-1). In the two feedlots examined, M. haemolytica exhibited considerable genetic diversity and limited resistance to common veterinary antibiotics. Garnering further information on the linkage between genotype and phenotype should contribute toward a better understanding of the pathogenesis and dissemination of M. haemolytica in feedlots.
authors.affiliation: Department of Biological Sciences, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada.
authors.forename: C L
authors.initials: CL
authors.lastname: Klima
authors.forename: T W
authors.initials: TW
authors.lastname: Alexander
authors.forename: R R
authors.initials: RR
authors.lastname: Read
authors.forename: S P
authors.initials: SP
authors.lastname: Gow
authors.forename: C W
authors.initials: CW
authors.lastname: Booker
authors.forename: S
authors.initials: S
authors.lastname: Hannon
authors.forename: C
authors.initials: C
authors.lastname: Sheedy
authors.forename: T A
authors.initials: TA
authors.lastname: McAllister
authors.forename: L B
authors.initials: LB
authors.lastname: Selinger
mesh_terms: D000416:Alberta; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle; D016000:Cluster Analysis; D024901:Drug Resistance, Multiple, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D005838:Genotype; D016978:Mannheimia haemolytica / Q000145:classification / Q000187:drug effects* / Q000235:genetics*; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D009305:Nasopharynx / Q000382:microbiology*; D010641:Phenotype; D016133:Polymerase Chain Reaction / Q000379:methods; D012703:Serotyping
chemical_list: D000900:Anti-Bacterial Agents