Genomic Comparison of Conjugative Plasmids from Salmonella enterica and Escherichia coli Encoding Beta-Lactamases and Capable of Mobilizing Kanamycin Resistance Col-like Plasmids

Elizabeth A Mcmillan,Jonathan G Frye,Lari M Hiott,Charlene R Jackson,Chin-Yi Chen,Poonam Sharma,Ly-Huong T Nguyen

doi:10.3390/microorganisms9112205

Abstract

Salmonella enterica and Escherichia coli are important human pathogens that frequently contain plasmids, both large and small, carrying antibiotic resistance genes. Large conjugative plasmids are known to mobilize small Col plasmids, but less is known about the specificity of mobilization. In the current study, six S. enterica and four E. coli strains containing large plasmids were tested for their ability to mobilize three different kanamycin resistance Col plasmids (KanR plasmids). Large conjugative plasmids from five isolates, four S. enterica and one E. coli, were able to mobilize KanR plasmids of various types. Plasmids capable of mobilizing the KanR plasmids were either IncI1 or IncX, while IncI1 and IncX plasmids with no evidence of conjugation had disrupted transfer regions. Conjugative plasmids of similar types mobilized similar KanR plasmids, but not all conjugative plasmid types were capable of mobilizing all of the KanR plasmids. These data describe some of the complexities and specificities of individual small plasmid mobilization.

Highlights

Both Salmonella enterica and Escherichia coli are common causes of foodborne illness in the United States and globally [1]
KanR plasmids were mobilized with varying success, de-can be the mids samepresent small plasmids
Plasmids and β-lactamase genes were identified in 10 isolates (n = 6 S. enterica and n = 4 E. coli)

Summary

Introduction

Both Salmonella enterica and Escherichia coli are common causes of foodborne illness in the United States and globally [1]. Β-lactamase genes, blaCMY-2 in particular, have been shown to frequently be carried by large plasmids especially of types IncA/C and IncI1 in Salmonella [5]. While many large plasmids are able to transfer to new cells independently via conjugation, not all plasmids are self-transmissible Mobilizable plasmids are those that cannot transfer via conjugation on their own, but require a “helper plasmid” possessing the necessary genes to encode the mate-pair structures which mobilizable plasmids can utilize to transfer to a new cell [6]. Mobilizable plasmids may utilize their own relaxase/nikase or those present on the conjugative helper plasmid [7,8]. Many large plasmids, such as types IncF, IncP, and IncI1, have proven capable of mobilizing small plasmids [9].

Methods

Results

Conclusion