660. Evaluation of Qvella’s FAST-Prep™ Liquid Colony™ for Early Antimicrobial Sensitivity Testing of Positive Blood Culture by Disk Diffusion Method

Abstract

Background Conventional antimicrobial susceptibility testing (AST) of microorganisms from positive blood cultures (PBC) can take ≥ 2 days. In order to improve the turnaround time for AST on a PBC, CLSI and EUCAST have made efforts to standardize procedures for disk diffusion (DD) direct from a PBC. Qvella Corporation (Richmond Hill, ON, Canada) has recently developed FAST-Prep, an automated centrifugal sample preparation system that rapidly delivers a Liquid Colony consisting of a purified, concentrated, viable cell suspension directly from a PBC. This study was performed to investigate the feasibility of DD AST off of a PBC using a FAST-Prep Liquid Colony. Methods Contrived PBC samples were prepared by spiking 6 species of Gram-positive and 4 species of Gram-negative bacteria (3-5 strains per species) into FA® Plus bottles and incubating in the BACT/ALERT® VIRTUO® System (bioMerieux, Durham, NC). After positivity, 3 mL of PBC was added to the FAST-Prep cartridge. After 20 minutes of processing in the FAST-Prep instrument, the Liquid Colony was removed from the cartridge and a 0.5 McFarland sample was prepared for DD AST. In parallel, the DD AST from a PBC was performed using 4 drops of PBC (CLSI direct method). Both methods were compared to conventional colony-based DD AST. After 16-18 hours of incubation zone diameters and S/I/R interpretations were determined. Categorical agreement (CA) and errors for both DD AST methods were calculated. In addition, colony plate counting was performed on 0.5 McFarland suspensions of Liquid Colony and the plate colony to determine biomass recovery and sample purity. Results CA for a FAST-Prep DD AST for Gram-positive and Gram-negative bacteria was 95.6% and 98.6%, respectively, compared to CA for CLSI DD AST of 77.2% and 81.9%, respectively. Biomass in the Liquid Colony was 7.2x108 and 1.2x109 CFU for Gram-positive and Gram-negative bacteria, respectively. Cell concentration in the 0.5 McFarland suspension of the Liquid Colony was 3.7x107 and 5.9x107 CFU/mL for Gram-positive and Gram-negative bacteria, respectively, which was similar to the concentration for the reference colony suspension. Conclusion The results support the potential role of FAST-Prep in providing a Liquid Colony for use in rapid AST. Disclosures Susan M. Novak-Weekley, PhD, D(ABMM), Qvella (Employee, Shareholder) Aye Aye Khine, PhD, Qvella (Employee, Shareholder) Tino Alavie, PhD, Qvella (Employee) Namidha Fernandez, MS, Qvella (Employee) Laxman Pandey, MS, Qvella (Employee) Abdossamad Talebpour, PhD, Qvella (Employee, Shareholder)

Evaluation of the Liquid Colony™ Produced by the FAST System for Shortening the Time of Bacterial Identification and Phenotypic Antimicrobial Susceptibility Testing and Detection of Resistance Mechanisms from Positive Blood Cultures

“…The data presented here reveal an excellent overall concordance of ID and AST results obtained with the LC compared with those obtained following a conventional protocol involving subculturing on solid media and processing of isolated colonies. The results were in overall agreement with those reported by previous studies [12][13][14][15]. Discordant ID results primarily involved PBCs containing coagulasenegative staphylococci, which often contain a mixture of species.…”

“…This was the first evaluation of the FAST System LC using reference broth microdilution as an AST method, while previous studies used automated AST systems (e.g., Vitek-2 [12,13] or BD Phoenix [14][15][16] or disk diffusion [15]). Automated systems are often preferred by diagnostic laboratories due to less manual handling and labor.…”

“…Nevertheless, automated AST systems may exhibit accuracy issues with some antibiotics, especially with MDR pathogens [17][18][19][20], while broth microdilution can also be handled using automated systems. Another original aspect of this study was the inclusion of a higher number of MDR pathogens compared with previous studies [12][13][14][15][16], reflecting the epidemiological setting. Despite the high percentage of MDR pathogens, it is worth noting that no VMEs were observed with Gram-positive bacteria, and only two VMEs were observed with Gram-negative bacteria.…”

Bacterial Infections in Intensive Care Units: Epidemiological and Microbiological Aspects

“…The obtained suspension can be used to rapidly obtain identification from MALDI-TOF and susceptibility profile from the colourimetric technique. The mentioned progress could constitute the last frontier in terms of rapid diagnostic methods, resulting in an untimely and complete microbiological report within 24 h from the positivity of the blood sample [ 101 , 102 , 103 ].…”