Characterization of two mobilizable plasmids isolated from enterobacter cloacae

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Third-generation cephalosporin resistance in Enterobacteriaceae is a growing public health concern.
• Metallo-beta-lactamases (MBLs) are a significant class of beta-lactamase enzymes contributing to antibiotic resistance.
• Enterobacter cloacae is a common opportunistic pathogen frequently associated with multidrug resistance.

Purpose of the Study:

• To characterize the plasmids harbored by a third-generation cephalosporin-resistant E. cloacae strain suspected of expressing metallo-beta-lactamase.
• To investigate the genetic content and potential functions of the isolated plasmids, pS51A and pS51B.

Main Methods:

• Isolation and structural analysis of plasmids pS51A (5782 bp) and pS51B (4854 bp).
• Bioinformatic analysis of plasmid-encoded genes, including replication origin (RNA I/RNA II) and relaxase genes (mobABCD).
• Homology search for metallo-beta-lactamase genes and identification of other open reading frames (ORFs).

Main Results:

• Two mobilizable plasmids, pS51A and pS51B, belonging to the ColE1 superfamily, were successfully isolated and characterized.
• Neither plasmid contained a metallo-beta-lactamase gene among their identified open reading frames.
• ORFs identified include genes related to plasmid replication, protein L, heat shock proteins, helix-turn-helix proteins, and replication initiation proteins from E. coli and Salmonella.

Conclusions:

• The study identified and characterized two novel plasmids, pS51A and pS51B, from a resistant E. cloacae strain.
• The absence of a metallo-beta-lactamase gene suggests alternative resistance mechanisms may be present in this strain.
• Stable maintenance of these plasmids in E. cloacae indicates their encoded functions likely provide a growth advantage to the host cell, potentially contributing to bacterial fitness and persistence.