Transferability of ESBL-encoding IncN and IncI1 plasmids among field strains of different Salmonella serovars and Escherichia coli

Authors: DORR, MACKENZIE - University Of Florida; SILVER, ARYEH - University Of Florida; SMURLICK, DYLAN - University Of Florida; ARUKHA, ANANTA - University Of Florida; KARIYAWASAM, SUBHASHINIE - University Of Florida; Oladeinde, Adelumola - Ade; COOK, KIMBERLY - US Department Of Agriculture (USDA); DENAGAMAGE, THOMAS - University Of Florida

Submitted to: Journal of Global Antimicrobial Resistance
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2022
Publication Date: 4/27/2022
Citation: Dorr, M., Silver, A., Smurlick, D., Arukha, A., Kariyawasam, S., Oladeinde, A.A., Cook, K., Denagamage, T. 2022. Transferability of ESBL-encoding IncN and IncI1 plasmids among field strains of different Salmonella serovars and Escherichia coli. Journal of Global Antimicrobial Resistance. 30:88-95. https://doi.org/10.1016/j.jgar.2022.04.015.
DOI: https://doi.org/10.1016/j.jgar.2022.04.015

Interpretive Summary: Extended spectrum cephalosporins are antibiotics often used as the last line of defense for treating enteric bacterial infections, particularly in children and immunocompromised individuals. Therefore, extended spectrum cephalosporins are considered the highest priority among the critically important antimicrobials by the World Health Organization and the U.S. Center for Disease Control and Prevention. The major vehicle used by enteric bacteria for the dissemination of resistance is plasmid-mediated horizontal gene transfer. Earlier studies have demonstrated that plasmids encoding antimicrobial resistance are frequently exchanged between laboratory strains of E. coli and Salmonella, however, the transferability potential of these plasmids among field strains are currently unknown. Therefore, the objective of this study was to determine the transmissibility rates of plasmids encoding genes for extended spectrum cephalosporin resistance between Salmonella and E. coli field strains. This study confirmed the ability and efficiency with which plasmids encoding extended spectrum cephalosporin resistant genes are transferred from Salmonella Heidelberg and E. coli strains to other field strains and other species of bacteria naturally present in poultry. This information is important for understanding the true public health threat posed by these plasmids and for implementing mitigation strategies to control their dissemination.

Technical Abstract: Objectives: This study aimed to sequence, assemble and annotate two plasmids (two IncN and one IncI1) carrying the blaCTX-M-1 gene and assess their transmissibility rates between homologous and heterologous serovars and/or species of bacteria. Methods: First, the plasmids were sequenced, assembled, and annotated. They were then transferred from three donor strains (E. coli/IncN, S. Heidelberg/IncN, and S. Heidelberg/IncI1) into nine recipient strains (S. Enteritidis, S. Heidelberg, S. Saint Paul, S. Cero, S. Infantis, S. Braenderup, E. coli 50, and E. coli 2010). The blaCTX-M-1 gene PCR, plasmid isolation, and antimicrobial susceptibility testing were used on the transconjugants to confirm the successful transfer of ESBL plasmids into the recipient strains. Results: Both IncN plasmids were 42,407 bp in size and showed '99.4% similarity to the S. Bredeney pET1.2-IncN whereas the IncI1 plasmid was 107,635 bp in size and demonstrated '99.9% similarity to the E. coli pCOV33 plasmid. Successful plasmid transfer was observed between donor E. coli (IncN) and all recipient strains except for E. coli 50 and between donor S. Heidelberg (IncN) and all recipient strains. Successful plasmid transfer was also observed between S. Heidelberg (IncI1) and E. coli 50. Conclusions: Transfer of the bla CTX-M-1 encoding IncN and IncI1 plasmids via conjugation is possible yet occurs at different frequencies depending on the donor strain of bacteria, with S. Heidelberg (IncN) having the highest donor-dependent transfer frequency, followed by E. coli 9079 (IncN) and S. Heidelberg (IncI1).