Horizontal gene transfer is the main driver of antimicrobial resistance in broiler chicks infected with Salmonella enterica Serovar Heidelberg

Authors: Oladeinde, Adelumola - Ade; ABDO, ZAID - Colorado State University; PRESS, MAXIMILIAN - Phase Genomics, Inc; Cook, Kimberly - Kim; Cox Jr, Nelson; ZWIRTZITZ, BENJAMIN - University Of Veterinary Medicine; WOYDA, REED - Colorado State University; LAKIN, STEVEN - Colorado State University; THOMAS IV, JESSE - Centers For Disease Control And Prevention (CDC) - United States; Looft, Torey; Cosby, Douglas; Hinton Jr, Arthur; Guard, Jean; Line, John; Rothrock, Michael; Berrang, Mark; HERRINGTON, KYLER - Medical College Georgia; ZOCK, GREGORY - University Of Georgia; Plumblee Lawrence, Jodie; Cudnik, Denice; House, Sandra; Ingram, Kimberly; LARISCY, LEAH - Orise Fellow; WAGNER, ROBERT - University Of Veterinary Medicine; AGGREY, SAMUEL - University Of Georgia; CHAI, LILONG - University Of Georgia; RITZ, CASEY - University Of Georgia

Submitted to: mSystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2021
Publication Date: 8/24/2021
Citation: Oladeinde, A.A., Abdo, Z., Press, M.O., Cook, K.L., Cox Jr, N.A., Zwirtzitz, B., Woyda, R., Lakin, S.M., Thomas Iv, J.C., Looft, T.P., Cosby, D.E., Hinton Jr, A., Guard, J.Y., Line, J.E., Rothrock Jr, M.J., Berrang, M.E., Herrington, K., Zock, G.S., Plumblee Lawrence, J.R., Cudnik, D., House, S.L., Ingram, K.D., Lariscy, L., Wagner, R., Aggrey, S.E., Chai, L., Ritz, C. 2021. Horizontal gene transfer is the main driver of antimicrobial resistance in broiler chicks infected with Salmonella enterica Serovar Heidelberg. mSystems. 6(4):e00729-21. https://doi.org/10.1128/mSystems.00729-21.
DOI: https://doi.org/10.1128/mSystems.00729-21

Interpretive Summary: The demand for antibiotic-free chicken has left the poultry industry in uncharted waters and forced the industry to invent new ways to curtail the prevalence of Salmonella. Consequently, there has been a push to increase the use of alternatives to antibiotics in pre-harvest broiler chicken production. These alternatives include acid-based litter and water treatments intended to create an unfavorable acidic environment for pathogens, and disinfectants for cleaner hatchery environment. However, the notion that antibiotic use in chicken production is responsible for an increase in antibiotic resistant Salmonella has never been questioned or tested in broiler chickens. Therefore, the goal of this study was to determine whether broiler chicks raised antibiotic-free carry antibiotic resistance that can be transferred to Salmonella. To do this, we inoculated one-day-old Cobb 500 broiler chicks with an antibiotic susceptible Salmonella enterica serovar Heidelberg (S. Heidelberg) strain and characterized the S. Heidelberg strains that colonized the gut and litter of broiler chicks two-weeks after inoculation. Our results confirmed that Salmonella can acquire antimicrobial resistance from the bacteria of broiler chicks raised without antibiotics. Furthermore, we identified exposure to acid and the age of the litter used for raising broiler chicks as important pre-harvest drivers of antibiotic resistance in Salmonella Heidelberg.

Technical Abstract: Salmonella enterica serovar Heidelberg (SH) is one of the prolific serovars causing poultry-associated food-borne illness in the world. They are a public health threat because of their promiscuity to plasmids that confer multidrug resistance to antibiotics of human health importance including plasmid-mediated AmpC (pAmpC) ß-lactamase. Although horizontal gene transfer (HGT) is the major mechanism responsible for an increase in antimicrobial resistance (AR) in Salmonella, the biology behind AR acquisition in SH is still unknown. Here, we show that one day old broiler chicks challenged with an antibiotic susceptible SH strain and raised without antibiotics carried multidrug resistance SH strains 14 days after challenge. We determined that horizontal acquisition of IncI1 plasmid multilocus sequence type 26 (pST26) from Escherichia coli strains to be the source of the AR phenotype. The transfer rate of pST26 and the broiler chicken bacterial community was affected by SH route of inoculation. Using in vitro agar mating experiments between SH and E. coli strains isolated from 2-week-old broiler chickens raised on fresh litter or reused litter, we confirmed that the transfer of pST26 was via conjugation. Conversely, pST12 carrying pAmpC was transferred through bacteriophage P22 transduction and evolved as a chimera of IncI1 and IncFIB/IncFII plasmids present in E. coli. Carriage of pST26 increased the fitness of SH under acidic selection pressure. Our results suggest that HGT shapes the evolution of AR in SH and that antibiotic use reduction alone is insufficient to limit AR plasmid transfer from commensal bacteria to Salmonella.