165. Impact of Limited Incubation of Bacterial Growth-Positive Cultures and Antibiotic Sensitivity Testing
Session: Poster Abstract Session: Diagnostics: Bacteremia
Thursday, October 27, 2016
Room: Poster Hall
Background: Rapid identification and assessment of antimicrobial susceptibility of bacterial organisms is a priority for the clinical microbiology lab. Previous investigations have found that testing of organisms cultivated after a limited incubation (4 to 6 hours) from blood samples of bacteremic patients can provide accurate identification by MALDI-TOF MS analysis and antibiotic susceptibility profile on commercial antibiotic susceptibility testing (AST) instruments. We aim to assess agreement of antibiotic susceptibility profiles from organisms tested after a limited incubation period and those tested at the manufacturer's recommendation of >18 hours of incubation. We also assess potential impact of limited incubation reporting on time to optimal antibiotic therapy.

Methods: A retrospective analysis of blood and body fluid samples from monomicrobial bacteremic patients was performed following standard analysis and reporting. Samples were processed by a limited incubation protocol in which subcultures were incubated for 5 hours prior to automated AST. Antibiotic susceptibility profiles were compared with profiles from standard incubation protocols for both essential and categorical agreement, with designation of discrepancy events as very major (wherein limited incubation sample reports as sensitive where the standard incubation sample reports as resistant), major (wherein limited sample is resistant and standard sample is sensitive), or minor (wherein one sample is indeterminate and the other is either resistant or sensitive). Subsequently, a retrospective review of inpatient cases from 5/1/2015 to 5/1/2016 determined if this strategy would impact time to optimal therapy for inpatients with monomicrobial bacteremia.

Results: 3682 antibiotic sensitivity or antibiotic screening test pairings were derived from 91 patients with monomicrobial bacteremia. 22 separate pathogens were isolated and used for antibiotic susceptibility analysis. A total accuracy rate of 98.45% was noted among limited incubation samples, with discrepancy rates of 0.27% Very Major, 0.14% Major, and 1.33% Minor.

Conclusion: A limited incubation method prior to antibiotic susceptibility testing is noninferior in a clinical microbiology lab and demonstrates strong agreement in comparison to standard incubation.

Daniel S Murrell, MD, Internal Medicine, University of Illinois at Chicago, Chicago, IL and Amanda Harrington, PhD, D(ABMM), Clinical Microbiology Service, University of Illinois at Chicago, Chicago, IL


D. S. Murrell, None

A. Harrington, None

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