APHL 2019 POSTER ABSTRACTS
NC) and “MIC test strip” (MTS) from Liofilchem (Waltham, MA),
containing meropenem, ceftazidime, and ceftazidime-avibactam.
Seventy-seven previously characterized CP-CRE isolates received at
the Minnesota Department of Health Public Health Laboratory were
tested comparing the two test strips.
Methods: All 77 isolates, collected from 2012-2018, had previously
tested positive by PCR for KPC, NDM, OXA-48-Like, VIM, or IMP
carbapenemases. A variety of organisms were chosen including
Citrobacter freundii, Escherichia coli, Klebsiella (Enterobacter)
aerogenes, Enterobacter cloacae, Klebsiella oxytoca, Klebsiella
pneumoniae, Leclercia adecarboxylata, Raoultella ornithinolytica,
Providencia rettgeri, Pseudomonas aeruginosa, and Serratia
marcescens. Frozen Isolates were subcultured and a 0.5 McFarland
standard was created for each isolate, which was evenly spread on
a Mueller-Hinton agar plate. Test strips were placed onto the agar
and incubated for 18 hours. The zone of inhibition was read per
product insert instructions.
Results: The test strips were compared using overall essential
agreement (EA) (results +/-1 doubling dilution), and categorical
agreement (CA) (same resistance category per CLSI breakpoints of
susceptible, intermediate, and resistant). When comparing the two
test strips, meropenem EA was 92.21% while the CA was 89.61%.
Ceftazidime EA and CA were both 98.70%. Ceftazidime-avibactam
EA was 96.10% while the CA was 100%.
Presenter: Bradley Craft, AR Fellow, Minnesota Department of
Health Public Health Laboratory, St. Paul., MN,
[email protected]
Complications in Bacterial Identification: When MALDI and
Conventional Identification Tests Don’t Agree
C. Harrison, S. LaVoie, L. Chicaiza, S. Nin, C-A. Da Costa-Carter and
J. Rakeman, New York City Public Health Laboratory
Matrix-assisted laser desorption/ionization time of flight mass
spectrometry (MALDI-TOF MS) has emerged as a rapid, reliable, and
low cost method for identification of many bacterial species, making
it a highly approachable method for use in clinical and public
health laboratories. Bacterial species identification is achieved
by ionization and vaporization of cellular proteins and comparing
observed spectrum to a database of reference spectra to generate
an identification confidence score that must meet a set threshold
to report results. Each MALDI system offers a clinical application
database containing a limited number of FDA cleared bacterial
species reference spectra and a much larger research use only
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LAB MATTERS Summer 2019
For bacterial isolates for which we cannot report a MALDI result,
bacteria are identified by FDA cleared conventional biochemical
testing, such as the RapID™ ANA II System (ThermoFisher) or the
API (bioMérieux) identification system. The spectral databases for
MALDI are routinely updated and require verification or validation
following each library update, while conventional biochemical
identification system databases are rarely updated. Conventional
testing methods are easy to setup but rely upon individual
interpretation of results to determine identification, introducing an
element of subjectivity. When discrepancies arise, they are often in
closely related species of the same genus as new strides are made
in improving MALDI spectra libraries. However, it raises the practical
questions around reporting and best practice when current systems
continue to evolve.
The goal of this study is to investigate the incidence of such
discrepant events at the New York City Public Health Laboratory.
Here we analyze specimens collected between August 2017 and
December 2018 from the Office of Chief Medical Examiner (OCME)
that were received for bacterial culture, and for which isolates were
analyzed by bioMérieux Vitek MS. A preliminary analysis suggests
that MALDI results did not agree with conventional testing methods
in as many as 9% of isolates, and did not report an identification
an additional 5% of the time. Of those that were discrepant, the
majority only differed by species, although 2% of total isolates
disagreed by genus and species. MALDI was not able to differentiate
between some species, requiring follow-up biochemical testing,
such as for Klebsiella variicola and Klebsiella pneumoniae.
Further analysis will focus on identifying common bacterial species
perpetuating this problem and any clinical significance in potentially
reporting the incorrect species identification in such cases. This
study highlights the complexity of reporting in such circumstances
and invites discussion around best practices.
Presenter: Christy Harrison, New York City Public Health Laboratory,
New York, NY, [email protected]
Enhanced Legionella Isolation Using Traditional Culture
Methods Augmented by Legiolert™
S. Hughes, J. Novak, I. Rubinstein, Y. Chekoff, S. Silver, E. Patricio,
J. Wang, A. DeVito, E. Gonzalez, E. Omoregie and J. Rakeman, New
York City Public Health Laboratory
In July 2018, the New York City Department of Health & Mental
Hygiene (NYC-DOHMH) identified a cluster of 27 cases of
Legionnaires’ disease (LD) in the Lower Washington Heights
neighborhood of NYC. Following remediation of cooling towers
suspected to be associated with the LD cases, another outbreak
of 32 cases of LD occurred in October 2018 in the same
neighborhood. Cumulative samples from both investigations
resulted in a combined total of 40 non-potable water samples
from 26 different cooling towers (CT) that were tested for the
purpose of isolating Legionella pneumophila serogroup 1 (Lp1)
and establishing a linkage with the clinical cases associated with
the outbreaks. Isolation of Lp1 from cooling tower water samples
enabled the identification and mitigation of environmental sources
of Lp1 that were a potential cause of these outbreaks. Additional
typing of CT and clinical isolates further implicated a single CT as
the potential source of the outbreak. Water samples tested during
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Conclusions: The results show that the test strips provided by
both companies compare well to each other. For ceftazidime and
ceftazidime-avibactam, the results for overall EA and CA were above
95% with the differences in overall EA having no effect on the CA.
Ceftazidime did have one isolate were there was no CA even though
there was overall EA, with an E-test result of intermediate and MTS
result of resistant. Meropenem had the most disagreement between
the two tests. Meropenem was more difficult to read with micro
colonies and macro colonies, both next to the strips and spread
throughout the zone of inhibition, which is a likely contributor to
the higher number of meropenem disagreements. While E-tests
have been available for longer, the MTS from Liofilchem provides
comparable results. While unable to determine which of the strips
was more accurate, the high agreement between the strips shows
that comparable results can be obtained with both.
(RUO) reference database with additional bacterial species spectra
that have not been FDA cleared.