Molecular characterization of a novel conjugative plasmid in Edwardsiella piscicida strain MS-18-199

Authors: ABDELHAMED, HOSSAM - Mississippi State University; RAMACHANDRAN, RESHMA - Mississippi State University; OZDEMIR, OZAN - Mississippi State University; Waldbieser, Geoffrey - Geoff; LAWRENCE, MARK - Mississippi State University

Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2019
Publication Date: 11/27/2019
Citation: Abdelhamed, H., Ramachandran, R., Ozdemir, O., Waldbieser, G.C., Lawrence, M.L. 2019. Molecular characterization of a novel conjugative plasmid in Edwardsiella piscicida strain MS-18-199. Frontiers in Cellular and Infection Microbiology. 9:404. https://doi.org/10.3389/fcimb.2019.00404.
DOI: https://doi.org/10.3389/fcimb.2019.00404

Interpretive Summary: Loss to disease is a major limitation to profitability of US aquaculture, and approximately 45% of inventory losses in catfish farms have been attributable to infection diseases. Feeds that contain antimicrobials can be used in restricted conditions, however, a multidrug resistant strain of the bacteria Edwardsiella piscida (MS-18-199) has been isolated from a catfish in eastern Mississippi. In order to determine the mechanisms of antimicrobial resistance, ARS scientists in Stoneville, Mississippi collaborated with scientists at Mississippi State University to produce a complete sequence of E piscicida MS-18-199. Complete genomic sequence of the isolate revealed a large (117,448 base pairs), novel plasmid that contained several antimicrobial resistance elements. The plasmid also demonstrated the capacity to be transferred from E. piscicida to E. ictaluri and E. coli in laboratory experiments. This research is the first report of a multiple drug resistant plasmid in E. piscicida in the US that warrants careful tracking in aquaculture systems to inform antimicrobial stewardship.

Technical Abstract: Edwardsiella piscicida is a pathogenic bacterium responsible for significant losses in important wild and cultured fish species. Moreover, E. piscicida has been isolated from other hosts, including birds, reptiles, and humans. E. piscicida strain MS-18-199 was recovered from a diseased catfish from East Mississippi and showed resistance to florfenicol, chloramphenicol, oxytetracycline, doxycycline, erythromycin, tetracycline, azitromycin, spectinomycin, sulfonamide, and bacitracin. To explore the mechanisms of resistance in E. piscicida strain MS-18-199, genomic DNA was extracted and subjected to whole genome sequencing (WGS) using a combination of long (Oxford Nanopore) and short (Illumina) reads. The genome of strain MS-18-199 revealed a novel plasmid named pEIMS-18199. The 117,448 bp plasmid contains several resistant (AMR) elements/genes, including florfenicol efflux pump (floR), tetracycline efflux pump (tetA), tetracycline repressor protein (tetR), sulfonamide resistance (sul2), aminoglycoside O-phosphotransferase aph(6)-Id (strB), and aminoglycoside O-phosphotransferase aph(3)-Ib (strA). Two genes, arsA and arsD, that encode protein components related to transport/resistance to arsenic were also found in pEIMS-18199. In addition, pEIMS-18199 carried twelve conjugative transfer genes (tra), eight transposases and insertion elements, two plasmid stability proteins, two replication proteins, and three partitioning proteins (par system). Results from mobilization and stability experiments revealed that pEIMS-18199 is highly stable in the host cell and could be transferred to Escherichia coli and Edwardsiella ictaluri by conjugation. To our knowledge, this is the first detection of a multidrug resistance (MDR) conjugative plasmid in E. piscicida in the United States. Careful tracking of this plasmid in the aquaculture system is warranted. Knowledge regarding the molecular mechanisms of AMR in aquaculture is important for antimicrobial stewardship.