Influence of tra genes of IncP and F plasmids on the mobilization of small Kanamycin resistance ColE1-Like plasmids in bacterial biofilms

Authors: Chen, Chinyi; Nguyen, Ly Huong

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/27/2017
Publication Date: 6/1/2017
Citation: Chen, C., Nguyen, L.T. 2017. Influence of tra genes of IncP and F plasmids on the mobilization of small Kanamycin resistance ColE1-Like plasmids in bacterial biofilms. American Society for Microbiology Annual Meeting. p.1.

Interpretive Summary:

Technical Abstract: Background: Horizontal gene transfer is a mechanism for movement of antibiotic resistance genes among bacteria. Some small kanamycin resistance (KanR) ColE1-like plasmids isolated from different serotypes of Salmonella enterica were shown to carry mobilization genes; although not self-transmissible, they can be mobilized in the presence of other conjugative plasmids. Methods: Eight KanR ColE1-like plasmid groups (A, B, C, C3, X, Y/Y2/Y3) were tested for their ability to be mobilized by the conjugal transfer (tra) genes of F and IncP plasmids using bi-parental or tri-parental (with helper strains) mating on agar plates. Plasmid mobilization was also tested in biofilms grown for different time periods and at different temperatures. Results: Different plasmid groups showed varied specificity and efficiency of mobilization by F or IncP tra genes. Group A plasmids, carrying the single mobA gene, can only be mobilized by F plasmid in cis inefficiently (approximately 3E-6) and was unable to be mobilized by either F or IncP tra genes via tri-parental mating on agar plates. Surprisingly, plasmid transfer was greatly enhanced in biofilms formed by donor strains carrying IncP tra genes, but was unchanged with the F tra genes. IncP tra genes can mobilize B and Y plasmids with high efficiencies (9E-1), but not those on the F plasmid. Plasmids C3 and X were efficiently (8E-1) mobilized by either IncP or F. However, biofilms did not enhance the transfer efficiency of these plasmids. Plasmid C, which lacks any known mob genes, can be very efficiently (7E-1) mobilized by tra genes from F plasmids via bi- or tri-parental mating, but not by IncP. And as with plasmid A, the transfer of plasmid C mediated by IncP was greatly improved in biofilms compared to agar plates. Conclusion: The efficient transfer of plasmid groups B, C3, X, and Y/Y2 mediated by either IncP or F was not enhanced (or slightly hindered) in biofilms. However, biofilms greatly improved the plasmid transfer of groups A and C by IncP. The age of the biofilms formed by donor strains is an important factor for efficient mobilization: younger (early log phase) cells showed optimal mobilization of plasmids in all cases. Thus it is crucial to evaluate plasmid transfer in different settings to understand the full potential impact of the transfer of antibiotic resistance genes on these plasmids into naïve strains.