Horizontal gene transfer and acquired antibiotic resistance in S. Heidelberg following in vitro incubation in broiler ceca

Authors: Oladeinde, Adelumola - Ade; Cook, Kimberly - Kim; LAKIN, STEVEN - Colorado State University; ABDO, ZAID - Colorado State University; Looft, Torey; HERRINGTON, KYLER - University Of Georgia; Zock, Gregory; Plumblee Lawrence, Jodie

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2019
Publication Date: 8/30/2019
Citation: Oladeinde, A.A., Cook, K.L., Lakin, S., Abdo, Z., Looft, T.P., Herrington, K., Zock, G.S., Plumblee Lawrence, J.R. 2019. Horizontal gene transfer and acquired antibiotic resistance in S. Heidelberg following in vitro incubation in broiler ceca. Applied and Environmental Microbiology. 85(22):e01903-19. https://doi.org/10.1128/AEM.01903-19.
DOI: https://doi.org/10.1128/AEM.01903-19

Interpretive Summary: S. Heidelberg is a clinically important serovar, linked to food-borne illness and among the top 5 serovars isolated from poultry in USA and Canada. Invasive infections with S. Heidelberg often require antimicrobial drug therapy including the administration of 3rd generation cephalosporins to individuals with fluoroquinolone contraindications. Increasing resistance to cephalosporins in S. Heidelberg isolates has been linked to the production of plasmid-mediated extended-spectrum or AmpC ß-lactamases. In this study, we show that S. Heidelberg could also acquire AmpC ß-lactamase via carriage of an IncB/O/K/Z encoding blaCMY-2 gene. To our knowledge, all IncB/O/K/Z plasmids reported so far have been found in E. coli strains, here we describe the first occurrence of an IncB/O/K/Z plasmid in S. Heidelberg acquired from broiler chicken cecal contents.

Technical Abstract: The chicken gastrointestinal tract (GIT) harbors taxa of microorganisms that play a role in the health and disease status of the host. The cecum is the part of the GIT that carries the highest microbial densities, has the longest residence time of digesta and is a vital site for urea recycling and water regulation. The cecum provides a rich environment for bacteria to horizontally transfer genes between one another via mobile genetic elements (MGE) such as plasmids and bacteriophages. In this study, we used broiler chicken cecum as a model to investigate MGE that can be transferred from chicken cecal populations to Salmonella enterica serovar Heidelberg (S. Heidelberg). We performed whole genome sequencing on isolates recovered after 0.5, 6, 24 and 48 h of incubation in ceca under microaerophilic conditions. We provide insights on genetic changes associated with phage-mediated DNA exchange between strains of the same bacterial lineage and characterized lysogenized bacteriophages carrying putative “moron” or fitness factor genes in S. Heidelberg. Finally, we performed an in-depth characterization and comparative genomics analysis of IncB/O/K/Z-like (88 kb) AmpC plasmid encoding extended ß-lactamase producing gene (blaCMY-2) that conferred resistance to first, second and third generation cephalosporins acquired by one S. Heidelberg isolate. This plasmid shared significant DNA homology with the IncK2 plasmids recovered from E. coli strains and was present in moderate to high copies. In vitro conjugation assay with IncB/O/K/Z-free S. Heidelberg and E. coli DH5a resulted in no transconjugants. Carriage of the plasmid posed a fitness cost on host cell; however, the plasmid was stable for 50 generations under ampicillin selection. This study provides insight into how plasmid and phage-mediated horizontal gene transfer can contribute to the persistence of S. Heidelberg in the chicken GIT.