Multiple E. coli sequence types contribute to the acquisition of IncI1 plasmids in Salmonella Heidelberg

Authors: Oladeinde, Adelumola - Ade; Cook, Kimberly - Kim; ABDO, ZAID - Colorado State University; WOYDA, REED - Colorado State University; LAKIN, STEVEN - Colorado State University; Plumblee Lawrence, Jodie; Cudnik, Denice; ZOCK, GREGORY - University Of Georgia

Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/2/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The incompatibility group I1 (IncI1) plasmids are often associated with antibiotic resistance and virulence and are mainly found in E. coli and nontyphoidal serovars of Salmonella isolated from poultry meat. IncI1 is the primary plasmid reported to encode AmpC ß-lactamase (blaCMY-2) in Salmonella enterica serovar Heidelberg (S. Heidelberg). However, the selective pressures or the donors of IncI1 plasmids in poultry production is not fully understood. The horizontal transfer (conjugation and transduction) of multidrug (MDR) resistance plasmids to a susceptible S. Heidelberg strain was determined in vitro in the absence of antibiotics using a consortium of E. coli strains recovered from the ceca of broiler chickens raised without antibiotics for 2 weeks. The E. coli consortium comprised of four sequence types (ST) (69, 93, 1403, 6858) and four phylogenetic groups (D, A, B1 and F). They carried multiple plasmids (2 – 5 plasmids/isolate from six major inc groups) and antibiotic resistance genes (ARG) that conferred resistance to aminoglycosides, tetracyclines, sulfonamides and ampicillin. Solid plate mating experiments were carried out using CHROMagarTM ECC supplemented with either synthetic 2-hexadecynoic acid (2-HDA) as a conjugation inhibitor (COIN) or sodium citrate as a transduction inhibitor (TRIN). Transconjugants and transductants were selected on brilliant green sulfur agar with either ampicillin or gentamicin added. Gentamicin resistance was acquired at low rates (~ 22 % conjugation frequency) and an IncI1 plasmid (plasmid Multi Locus Sequence Type (pMLST) 26; clonal complex 2) carried by E. coli donor ST 6858 (phylogroup F) was identified as the MDR plasmid acquired. In contrast, ampicillin resistance was acquired at a sufficiently higher rate (~ 57 % transduction frequency). In this case, an IncI1 plasmid (pMLST 12) carrying blaCMY-2/blaCMY-61 was responsible for resistance to multiple ß-lactam antibiotics including ampicillin. The pMLST 12 plasmid was determined to have evolved from a recombination event between pMLST 26, IncI1 (unknown ST) present in E. coli ST 69 (phylogroup D) and a chromosomal region present in all four E. coli strains encoding blc-sugE-ampC genes. The transfer of both plasmids was inhibited with sodium citrate. These results suggest that reducing antibiotic use alone in poultry is likely insufficient to limit IncI1 plasmid transfer to S. Heidelberg. Therefore, the use of conjugation and transduction inhibitors would be an effective strategy to limit the horizontal transfer of epidemic IncI1 plasmids.