Abstract
Rapid identification and antimicrobial susceptibility testing of microorganisms causing bloodstream infections or sepsis have the potential to improve patient care. This proof-of-principle study evaluates the Lysis-Filtration Method for identification as well as antimicrobial susceptibility testing of bacteria directly from positive blood culture bottles in a clinical setting. A total of 100 non-duplicated positive blood cultures were tested and 1012 microorganism-antimicrobial combinations were assessed. An aliquot of non-charcoal blood culture broth was incubated with lysis buffer briefly before being filtered and washed. Microorganisms recovered from the filter membrane were first identified by using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight VITEK® Mass Spectrometry (VITEK MS). After quick identification from VITEK MS, filtered microorganisms were inoculated to VITEK®2 system for full panel antimicrobial susceptibility testing analysis. Of 100 bottles tested, the VITEK MS resulted in 94.0% correct organism identification to the species level. Compared to the conventional antimicrobial susceptibility testing methods, direct antimicrobial susceptibility testing from VITEK®2 resulted in 93.5% (946/1012) category agreement of antimicrobials tested, with 3.6% (36/1012) minor error, 1.7% (7/1012) major error, and 1.3% (13/1012) very major error of antimicrobials. The average time to identification and antimicrobial susceptibility testing was 11.4 hours by using the Lysis-Filtration method for both VITEK MS and VITEK®2 compared to 56.3 hours by using conventional methods (p<0.00001). Thus, the same-day results of microorganism identification and antimicrobial susceptibility testing directly from positive blood culture can be achieved and can be used for appropriate antibiotic therapy and antibiotic stewardship.
Highlights
Initiation of antimicrobial therapy is vital to the treatment of bloodstream infections and sepsis [1,2,3,4,5,6,7] which cause morbidity and mortality [1,2,3,4,5]
Aliquot taken from positive blood culture bottles were processed using the Lysis-Filtration Method (LFM) for direct ID by VITEK MS and full panel antimicrobial susceptibility testing (AST) by VITEK2
Direct Microorganism Identification A total of 100 positive blood cultures from 100 patients were included in the study, consisting of 47 Gram positive, 49 Gram negative, and 4 yeast isolates
Summary
Initiation of antimicrobial therapy is vital to the treatment of bloodstream infections and sepsis [1,2,3,4,5,6,7] which cause morbidity and mortality [1,2,3,4,5]. Conventional ID includes growth and biochemical characteristics from culture media, or generated by commercial ID systems, which will take up to two days for many microorganisms and longer for others such as yeasts [3,6,7,8,9,10]. Molecular methods such as DNA microarrays, fluorescent in-situ hybridization, and realtime polymerase chain reaction (RT-PCR) have shown to be efficient for the identification of specific microorganism. Molecular methods lack the ability to identify a broad range of microorganisms and antimicrobial resistance [6,8]
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