APHL 2018 Annual Meeting Poster Abstracts
Reliable Identification Methods for Carbapenem-resistant
Carbapenemase-producing Acinetobacter (CP–CRA) Laboratory Surveillance of Enterobacteriaceae Isolated
from Patients in Tennessee
J. Dale and P. Snippes-Vagnone, Minnesota Department of Health
Public Health Laboratory, St. Paul, MN (complete abstract in Infectious Disease, p. 76)
Antibiotic resistance is a worldwide concern impacting the
healthcare system with difficult to treat infections. An emerging
threat is resistance to the carbapenem class of antibiotics,
which has resulted in surveillance efforts to understand the
prevalence and epidemiology of carbapenem resistant organisms.
Acinetobacter baumannii is a hospital-associated, opportunistic
pathogen with both intrinsic and acquired antibiotic resistance
mechanisms. Carbapenemase-producing carbapenem-resistant
Acinetobacter spp. (CP-CRA) often harbor carbapenemase genes
on a plasmid that has the potential to transfer between bacterial
species and genera. The prevalence of CP-CRA containing plasmid-
encoded carbapenemases is poorly understood and the clinical
significance is unclear. Therefore, it is imperative that efforts are
taken to detect the carbapenem resistance mechanisms of CP-CRA
to aid in infection control measures. Fundamental to treatment and
control of CP-CRA are phenotypic and nucleic acid-based methods
for carbapenemase detection. Here we used established phenotypic
methods for carbapenemase detection, in conjunction with real-
time PCR (RT-PCR) for Acinetobacter blaOXA ß-lactamase genes, to
identify correlations between phenotype and genotype and provide
insight into the clinical significance of CP-CRA. The carbapenem
inactivation method (CIM) and modified CIM (mCIM) are phenotypic
tests performed routinely for the detection of carbapenemase
production in Enterobacteriaceae; however, these methods are
unreliable for use with Acinetobacter spp. Therefore, we opted to re-
examine the interpretive guidelines for carbapenemase production
of CRA by comparing CIM and mCIM results with data obtained
from RT-PCR detecting the presence of Acinetobacter plasmid-
associated blaOXA genes (OXA-23, -24/40, -58) and the intrinsic
blaOXA gene (OXA-51). We concur with the literature that the mCIM
is not reliable for detecting CP-CRA. However, our data demonstrates
that the interpretive criteria for CIM positive Acinetobacter spp.
should include any zone size with colonies spread throughout the
zone of inhibition. Use of the new interpretation strongly correlates
w ith the identification of an Acinetobacter blaOXA gene. There are
some isolates that harbor a blaOXA gene, but are CIM negative,
requiring further molecular testing to determine gene expression
levels that could explain the negative phenotype. In addition, the
chromosomal or plasmid location of each blaOXA gene needs to
be determined along with its capability for horizontal gene transfer
(HGT). Overall, our data provide strong evidence that CIM results are
a reliable indicator for CP-CRA and accurately predict the presence
of a blaOXA gene. The identification of a CP-CRA isolate harboring a
blaOXA gene, which may be plasmid-associated, is highly important
considering the possibility of HGT to other pathogens. Genomic Investigation of a Protracted Carbapenem-
Resistant Enterobacter aerogenes Outbreak in a Cardiac
ICU at a Tertiary Care Center in Rochester, New York
Presenter: Jennifer Dale, PhD, Minnesota Department of Health
Public Health Laboratory, St. Paul, MN, Phone: 612.201.5043,
Email: [email protected]
Comparison of ETEST ® and Broth Microdilution Methods for
Antimicrobial Susceptibility Testing of Shigella sp. Isolates
in New York City
(complete abstract in Food Safety, p. 58)
40
LAB MATTERS Summer 2018
A. Malek, S. Taffner, H. Mostafa, J. Wang, S. Petry, L. Fine, P.
Graman, D. Hardy, N. Pecora; University of Rochester Medical
Center, Rochester, NY
Background: Enterobacter spp. are significant nosocomial
pathogens associated with outbreaks in intensive care units
(ICUs). Between Jun-Oct 2017, carbapenem-resistant Enterobacter
aerogenes (CR-EA) strains were isolated from patients in our cardiac
ICU (CICU). Whole genome sequencing (WGS) of CR-EA isolates was
undertaken to investigate patient-to-patient transmission, assess
phylogeny relative to global strains and characterize molecular
determinants of resistance and virulence.
Methods: 22 CR-EA strains (12 outbreak, 10 other wards) were
sequenced (Illumina Miseq) and investigated for phylogenetic
relatedness by whole genome multi-locus sequence typing (wgMLST)
using Ridom ® Seqsphere+ and the CFSAN SNP pipeline. To establish
phylogeny with global E. aerogenes strains, 113 publically-available
sequences were used for comparison using HARVEST genomics
suite. Markers for antibiotic resistance and virulence factors were
identified using curated databases.
Results: WgMLST and core-SNP analyses revealed every CICU CR-
EA isolate to be part of a single clonal cluster, grouping distantly
from strains isolated from other wards and previous years. Barring
a single 2015 strain, harboring an nmcAR locus, none of the CR-
EA strains isolated from our hospital harbored genes encoding
carbapenemases. Some CICU strains harbored mutations resulting
in premature stop codons in outer membrane porin genes (omp36),
likely contributing to the carbapenem resistant phenotype. Virulome
analysis revealed the CICU strains to harbor genes encoding
yersiniabactin and colibactin systems on the ICEKp10 pathogenicity
island.
Conclusions: Carbapenem-resistant Enterobacteriaceae are a major
public health concern, with rapid spread attributed to the production
of mobilizable carbapenemases. Here, we describe a hospital ward
outbreak involving a clonal group of E. aerogenes carbapenemase
non-producing strains. Virulence and resistance determinants
underlying infections by Enterobacter spp. are poorly understood
and the latter may involve mechanisms such as porin disruption
and/or AmpC cephalosporinase overproduction, which present
complex diagnostic and management challenges. Yersiniabactin
and colibactin systems have been implicated in the invasiveness
of hyper-virulent Klebsiella pneumoniae. Intact clusters of these
components in the CICU outbreak strains may indicate a role for these
loci in enhanced survival and effective transmission in a subset of E.
aerogenes lineages. Prospective WGS presents a powerful resource
to complement traditional epidemiology in helping hospitals and
public health institutions track transmission events and assess the
effectiveness of control measures in real-time.
Presenter: Adel Malek, University of Rochester Medical Center,
Department of Pathology and Laboratory Medicine, Rochester, NY,
Email: [email protected]
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