Lab Matters Summer 2019 - Page 66

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, bradley.craft@state.mn.us 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 64 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, charrison4@health.nyc.gov 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 PublicHealthLabs @APHL APHL.org 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.