Direct disk diffusion test using European Clinical Antimicrobial Susceptibility Testing breakpoints provides reliable results compared with the standard method

Abstract

Sepsis represents a life-threatening infection requiring the immediate start of antibacterial treatment to reduce morbidity. Thus, laboratories use direct antimicrobial susceptibility testing (AST) to rapidly generate preliminary results from positive blood cultures. As the direct AST has not yet been published to be evaluated with EUCAST breakpoints, the purpose of the study was to investigate the reliability of the direct agar diffusion test to correctly produce AST results from positive monobacterial blood cultures compared with the VITEK2-based definitive AST, when current EUCAST breakpoints were used.A total of 428 isolates from unselected monobacterial routine blood cultures and 110 challenge strains were included. Direct agar diffusion-based and standard VITEK2-based AST of 2803 bacterium-drug combinations yielded a total clinical category agreement of 95.47% with 1.28% very major errors and 3.42% combined major and minor errors. On the species level, very major errors were observed in the species-drug combinations Enterococcus spp.-high-level gentamicin (10.87%) and Staphylococcus spp.-rifampicin (5%), only. No very major errors occurred with Enterobacteriaceae and Pseudomonas aeruginosa.In most species-drug combinations, the direct agar diffusion test using EUCAST breakpoints precisely predicted the result of the definitive antibiotic susceptibility test and, thus, it can be used to optimize empiric antibiotic therapy until definitive results are available.

Nasogastric feeding tubes from a neonatal department yield high concentrations of potentially pathogenic bacteria— even 1 d after insertion

“…Hence, all isolates with a count of more than 1,000 CFU/ml were identified by the VITEK 2 system (Biomérieux, Marcy l' etoile, France) complemented with standard laboratory methods or MALDI-TOF (MALDI Biotyper, Bruker, Billerica, MA), when the VITEK system failed to provide an acceptable identification. We tested Gram-negative rods for antibiotic susceptibility by the disc diffusion method according to European Clinical Antimicrobial Susceptibility Testing guidelines (27). We tested with the following Neo-sensitabs (Rosco Diagnostika, Taastrup, Denmark): Ampicillin (33 µg), Cefuroxime (60 µg), Cefotaxime (30 µg), Gentamicin (10 µg), Piperacillin-Tazobactam (30 μg + 6 μg), SulfamethoxazoleTrimethoprim (240 μg + 5.2 μg), Ciprofloxacin (5 µg), and Meropenem (10 µg).…”

Evaluation of performance of direct disk diffusion test from positively flagged blood culture broth: A large scale study from South India

“…CLSI, British Society of Antimicrobial Chemotherapy Guidelines, and European Committee on AST have proposed several methods to perform dDD. [6716] However, there is a lack of large scale studies and guidelines on reporting of dDD results. Furthermore, the CA and disagreement can have interlaboratory variation based on the methodology followed for performing dDD and the type of automated blood culture bottles used.…”

“…As per the standard practice in most of the blood culture laboratory, it takes around 48 h to report antibiotic sensitivity results after a blood culture bottle is flagged positive by automated system. [67] By performing direct susceptibility test from positive blood culture bottles, for example, direct disk diffusion (dDD) test, the TAT to generate antibiotic sensitivity report can reduce to 24 h. However, there is a grave need to address the problems associated with the methodology of performing and reporting dDD.…”

Genetic antimicrobial susceptibility testing in Gram‐negative sepsis – impact on time to results in a routine laboratory

“…Several variant approaches for direct AST by disk diffusion have been published previously . The protocol described herein has been used in our laboratory for more than 15 years for susceptibility categorization (S, I and R) of Enterobacteriaceae and shows an almost complete correlation with the final AST: The inoculum for the direct AST was prepared by adding two drops of blood (approximately 0.1 mL) from the blood culture bottle to 5 mL of saline.…”