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

Abstract

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.