Comparison of rapid antimicrobial susceptibility testing of flash positive blood culture bottles using disk diffusion and automated broth microdilution on VITEK 2 compact with standard methods: Clinical Laboratory Standards Institute (CLSI) protocol

BACKGROUND: Sepsis requires prompt diagnosis for effective management. Standard Antimicrobial Susceptibility Testing (AST) is time-consuming, highlighting the need for Rapid Antimicrobial Susceptibility Testing (RAST) to provide reports earlier. PURPOSE: To compare the results of RAST and AST in order to determine the feasibility and reliability of RAST. MATERIALS AND METHODS: A study at a tertiary care facility analyzed 95 positive blood culture isolates. RAST was performed by Disk Diffusion (DD) and VITEK 2 Compact Automated Broth Microdilution (BMD) from flagged positive broth. In contrast, AST was performed by DD and BMD from isolated colonies. RESULTS: Among 95 Gram-negative bacteria (GNB), E. coli (n = 40), and K. pneumoniae (n = 19) were most common. RAST vs AST DD for GNB showed 91 % Categorical agreement (CA) with an overall Very Major Error (VME) and Major Error (ME) rates of 0.7 % & 2.2 % and respectively. For GNB, RAST vs. AST BMD demonstrated a CA of 97 % and Essential Agreement (EA) of 97.7 %, with VME and ME rates of 1.7 % (excluding E.coli + Cefepime drug bug pairs) and 0.1 % respectively. CONCLUSION: These findings suggest that RAST is a reliable antimicrobial susceptibility tool for GNB from direct Blood Culture broths. RAST can support early initiation of targeted antimicrobial therapy in patients with sepsis.