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Int J Antimicrob Agents. 2019 Mar 6. pii: S0924-8579(19)30039-1. doi: 10.1016/j.ijantimicag.2019.02.009. [Epub ahead of print]

Molecular characterization and evolution of the first outbreak of vancomycin resistant Enterococcus faecium in Western Australia.

Author information

1
Antimicrobial Resistance and Infectious Diseases (AMRID) Research Laboratory, Murdoch University, Western Australia.
2
Antimicrobial Resistance and Infectious Diseases (AMRID) Research Laboratory, Murdoch University, Western Australia. Electronic address: G.coombs@murdoch.edu.au.

Abstract

In 2001, Western Australia recorded its first outbreak of vancomycin resistant Enterococcus faecium (VREfm). A state-wide infection control effort, which oversaw patient screening and transfers, successfully terminated the outbreak within six months. However, the outbreak re-emerged two years later. Over the two outbreaks, the vanB-positive multilocus sequence type (ST) 173 E. faecium strain, was isolated from 201 patients. Our objective was to identify differences in genetic traits leading to the successful transmission of ST173 VREfm compared to non-ST173 VREfm isolated during the same period. Additionally, we aimed to describe the changes observed in the ST173 VREfm genome collected during the two outbreaks. Virulence factors ecbA, fss3, psaA and scm, identified in the non-ST173 isolates were largely absent in the ST173 isolates. The esp gene was not identified beyond 45% coverage for any isolate in this study. In terms of resistance genes, tet(U) was identified in 94.7% of ST173 VREfm isolated in the first outbreak but was largely absent in the ST173 VREfm isolated in the second outbreak and in the non-ST173 VREfm. Seven ST173 VREfm isolates (Clade A) carried dfrG but not tet(M) resistance genes. The average genome size of ST173 VREfm isolated in the first outbreak was significantly larger than the genome of the ST173 VREfm isolated in the second outbreak. The reduced number of virulence factors in the ST173 isolates may explain the low infection and high colonization rates observed during the outbreak. In addition, isolates with larger genome sizes were found to be associated with outbreaks.

KEYWORDS:

Antimicrobial resistance; Enterococcus faecium; Genetic Evolution; Outbreak

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