Browsing by Author "Liljebjelke, Karen A."

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    Comparative genomic analysis of mobile genetic elements in Histophilus somni isolates from feedlot cattle
    (2020-08-25) Mostafa Nazari Zanjani, Mohammad; Liljebjelke, Karen A.; McAllister, Tim A.; Schryvers, Anthony Bernard
    Organisms, including bacteria, are defined by the genes they possess. This genomic pool determines whether a bacterial species can survive or compete in a changing environment. Bacteria can acquire new genomic content through de novo mutations or through external genomic reservoirs via horizontal gene transfer. Horizontal gene transfer (HGT) is the exchange of genetic material through mobile genetic elements (MGE) between cells which have no parent-offspring relationship. The conjugation pathway is one of the main routes of HGT in bacteria and is in part mediated by plasmids or integrative and conjugative elements (ICE). ICEs can provide new genes through HGT which confer new phenotypic traits such as resistance to antibiotics and heavy metals, biofilm-formation and metabolic alterations. In this study, an ICE was identified in Histophilus somni, a Gram-negative bacterium that is one of the major bacteria involved in bovine respiratory disease (BRD). The ICE and other mobile genetic elements were identified through analysis of whole-genome sequences (WGS) of H. somni isolates collected from tissue samples from Canadian and American feedlot cattle mortalities. A variety of antimicrobial resistance genes were located within ICE sequences. AMR genes tet(H), Sul2/folP, APH(3”)-Ib, APH(6)-Id, and APH(3’’)-Ia, were identified. These genes may provide phenotypic resistance for the antimicrobial classes: tetracyclines, sulfonamides, phenicols and aminoglycosides. Plasmids were not identified in WGS files. No AMR genes were found on the chromosome other than those within ICE sequences. The ICEs in Canadian and American H. somni isolates exhibited similar genome assembly and genome content. The similarity of the ICE in Canadian and American H. somni isolates indicates that they may have moved between the two countries during import and export of cattle. The ICEs of H. somni were identified as members of the ICEHin1056 ICE-family. ICEs of the ICEHin1056 ICE-family have been identified in four bacterial species; two human-specific species, Haemophilus influenzae, and Haemophilus parainfluenzae, and the animal pathogens, H. somni, Actinobacillus pleuropneumoniae, M. haemolytica, and P. multocida.
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    Investigation of the Co-occurrence of Zinc and Copper Resistance and Antimicrobial Resistance in Escherichia coli from Beef Cattle Production Systems
    (2020-09-21) Guardado Servellón, Fernando Joaquín; Liljebjelke, Karen A.; Checkley, Sylvia L.; Turner, Raymond Joseph; Harrison, Joe J.
    The present set of studies was directed towards determining the relationship between zinc (Zn) and copper (Cu) resistance and antimicrobial resistance in Escherichia coli from beef cattle production systems. First, a spectrophotometric assay was developed to properly assess the resistance levels of both Zn and Cu in Escherichia coli. The method was standardized for E. coli and it displayed a good linear dynamic range (R2>0.95), and precision (RSD< 35% in all but three Zn concentrations). The MIC for the E. coli reference strain (ATCC 25922) were 2.78 mol/ml and 8.41 mol/ml for Zn and Cu respectively. In the second study, we determined antimicrobial phenotypes and the Zn and Cu resistance levels for E. coli isolates from environmental samples obtained from W.A Ranches. The samples analyzed had a low prevalence of antimicrobial resistance as 31/39 isolates were susceptible to all the antimicrobials tested using the disc diffusion method. The most common resistance was ampicillin (4/39) and amoxicillin-clavulanic acid (4/39), with one isolate being resistant to doxycycline. All the isolates resistant to ampicillin were also resistant to amoxicillin-clavulanic acid. The isolates were then tested for Zn and Cu resistance using the assay developed. Seven of the eight isolates with resistant or intermediate antimicrobial resistance patterns showed higher optical density (OD) in the Zn and Cu resistance spectrophotometric assay when compared to the reference strain. Fisher’s exact test was conducted to compare antimicrobial-resistant (all antimicrobials) and susceptible isolates in their resistance to Zn and Cu, with the results showing that the antimicrobial-resistant isolates are also more likely to have a higher resistance to Zn (p value<0.001) and Cu (p value=0.013) as indicated by higher absorbance units (AU). A Principal Component Analysis showed the clustering of 6/8 antimicrobial-resistant isolates based on the Zn and Cu resistance meaning that resistance to these metals might be an indicator of antimicrobial resistance.