Dissemination
of plasmid-borne resistance genes is influenced by various factors including
the genetic context of the gene itself, the transmission dynamics of the
plasmid lineage/s carrying the gene and the relative success of the host
bacterial strain. blaCMY-2
(and minor variants) is one of the most successful plasmid-borne β-lactamase
genes worldwide, particularly in Escherichia
coli, conferring resistance to both cephalosporins and β-lactamase
inhibitors. Several plasmid lineages have been reported to carry blaCMY-2, including IncI1,
IncA/C, IncF and IncK, but local epidemiological patterns vary. We investigated
the epidemiology of blaCMY-2-like
genes in E. coli strains from Sydney,
Australia over two time periods (2005-09; 2013-14) to gain insight into the
dynamics of their spread. Clinical E.
coli strains (n=103) were characterised by multilocus sequence typing,
PCR-based replicon typing, multiplex resistance gene PCR and Southern
hybridisation and a subset were sequenced using Illumina MiSeq technology. Horizontal
plasmid spread appeared to be an important mode of transmission in the earlier
time period (2005-09) as blaCMY-2was predominantly carried by IncI1
plasmids in diverse E. coli strains,
with few differences across the backbones of those plasmids that were sequenced.
In contrast, blaCMY-2 was
found inserted in the chromosome in half of the recent E. coli strains (2013-14) and very few of these contained IncI1
plasmids. Further analysis will reveal whether these strains are clonally related,
potentially representing a local outbreak, or whether different clonal lineages
have acquired a chromosomal blaCMY-2-like
gene independently. These preliminary findings suggest that the epidemiology of
blaCMY-2-like genes is
complex, involving both plasmid spread and clonal expansion of host E. coli strains, and that the dynamics
of transmission may be changing over time. The potential shift to chromosomally-located
blaCMY-2 represents a major
therapeutic concern.