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Implications of Oxacillin-Resistant, mecA-Negative Staphylococcus aureus Detected in NICU MRSA Surveillance Cultures

Published online by Cambridge University Press:  02 November 2020

Geoffrey Ikpeama
Affiliation:
BJC Healthcare - St. Louis Children’s Hospital
Crystal Squires
Affiliation:
BJH Microbiology Laboratory
Meghan Wallace
Affiliation:
Washington University School of Medicine
Patricia Kieffer
Affiliation:
St. Louis Childrenld_amp
Ericka Hayes
Affiliation:
Washington University School of Medicine in St. Louis/St. Louis Children’s Hospital
Eric Ransom
Affiliation:
Washington University School of Medicine
Carey-Ann Burnham
Affiliation:
Washington University School of Medicine
Patrick Reich
Affiliation:
Washington University School of Medicine
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Abstract

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Background: Weekly surveillance to identify neonatal intensive care unit (NICU) infants with methicillin-resistant S. aureus (MRSA) nasal colonization was performed using Remel Spectra MRSA chromogenic media. An increased MRSA colonization rate from baseline was detected in 2019, prompting additional review of all positive MRSA NICU screening cultures from 2019. Methods: A subset of 23 positive cultures were interrogated in detail. Species-level identification was confirmed using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) with a Bruker Biotyper. Penicillin-binding protein 2a (PBP2a) testing was performed using the Alere culture colony test, and cefoxitin and oxacillin susceptibility were assessed via Kirby-Bauer disk-diffusion methods (for the purpose of this analysis, oxacillin zone sizes 18 mm were considered susceptible). Molecular detection of mecA and mecC genes using PCR was performed. Results: All 23 isolates in the subset group were confirmed as S. aureus based on MALDI-TOF testing. Moreover, 8 isolates (35%) were confirmed as MRSA based on cefoxitin susceptibility, positive rapid PBP2a testing, and mecA PCR results. Overall, 15 isolates (65%) tested cefoxitin-susceptible and PBP2a negative with negative mecA and mecC gene testing. Of these, 1 (7%) tested oxacillin-susceptible based on disk-diffusion testing, consistent with methicillin-susceptible S. aureus (MSSA). The remaining 14 isolates (93%) tested oxacillin resistant based on oxacillin zone size. Conclusions: Our findings indicate the detection of mecA/mecC negative S. aureus isolates demonstrating oxacillin resistance and growth on Remel Spectra MRSA chromogenic media. These results have important implications for infection prevention surveillance efforts to detect MRSA and raise questions regarding optimal antibiotic therapy in patients with isolates displaying this phenotype.

Funding: None

Disclosures: None

Type
Poster Presentations
Copyright
© 2020 by The Society for Healthcare Epidemiology of America. All rights reserved.