Evaluation of BD Phoenix and VITEK 2 for direct and routine antimicrobial susceptibility from positive blood culture bottles.

OBJECTIVES

This study aims to comparatively evaluate the reliability of BD Phoenix and VITEK 2 systems for direct, routine and standard antimicrobial susceptibility testing (AST) of ESKAPE isolates from positive blood culture bottles, with a primary focus on the interpretation of results into susceptible, intermediate, or resistant categories.

METHODS

A total of 128 ESKAPE isolates from positive blood culture bottles were subjected to direct, routine and standard AST. Direct AST (DAST) and routine AST (RAST) were performed using BD Phoenix and VITEK 2 automated systems. DAST was conducted using a bacterial pellet obtained directly from positive blood cultures, while RAST used a colony after subculture. Results of both were compared based on categorical agreement (CA) and discrepancies. RAST results were further evaluated against standard AST (SAST), performed via the Kirby-Bauer disc diffusion assay using 24 h-grown colonies.

FINDINGS AND RESULTS

The AST categorical agreements (CA) of DAST with the RAST using BD Phoenix automated system for Enterobacterales, Non-fermenting, and Gram-positive cocci (S. aureus and Enterococci spp.) were 95.3 %, 100 %, and 100 % respectively, while 94.8 %, 94.7 %, 80 % and 100 % respectively in VITEK 2. CA between RAST and SAST is 86.9 %, 95.3 %, 100 %, and 82.3 % respectively with BD Phoenix, while 91.8 %, 91.9 %, 85.7 %, and 84.6 % respectively with VITEK 2, on the same group of bacteria. The VITEK 2 automated system showed consistency of results with >90 % CA suggesting high reliability for both direct and routine AST in Gram-negative bacteria.

CONCLUSION

VITEK 2 demonstrated consistently high reliability for both direct and routine AST in Gram-negative bacteria. The BD phoenix showed high reliability for direct AST only, across all organisms tested. Direct AST protocol established in this study is simple, cost-effective, reliable, and rapid techniques reducing turnaround time (TAT) by 24 h and potentially improving patient's outcome.