Evaluation of the performance of rapid antibiotic susceptibility test results using the disk diffusion directly from the positive blood culture bottles.

Purpose: In this study, we aimed to evaluate the compliance of rapid antibiotic susceptibility test (RAST) and conventional laboratory procedures.

Methods: The RAST was performed directly from the blood cultures of 71 Gram negative bacilli (GNB) and 38 Gram positive cocci (GPC) isolates. The results were evaluated at fourth, sixth and eighth hour. Categorical agreement (CA), very major error (VME), major error (ME) and minor error (mE) were calculated and compared with the results of conventional Vitek-2 system.

Results: Categorical agreement was detected ≥90 in cefotaxime and meropenem at fourth hour in Escherichia coli isolates. An encourage positive CA results were obtained from meropenem, ceftazidime and ciprofloxacin at the fourth hour in Klebsiella pneumoniae isolates. CA was compatible in imipenem, ciprofloxacin, gentamicin, and tobramycin for Pseudomonas aeruginosa at sixth hour. CA was low (<90%) in piperacillin-tazobactam for E. coli and K. pneumoniae, and meropenem in P. aeruginosa isolates. A good CA (≥90) with all tested antibiotics were found at all hours for Acinetobacter baumannii and also very high CA (100%) was detected at sixth and eighth hour in Staphylococcus aureus isolates. CA remained below the standard criteria at fourth hour in vancomycin and high level gentamicin, in addition to imipenem at sixth hours in enterococci isolates. VME and ME were not detected and mE was 12.7% in GNB and 50% in GPC at eighth hour.

Conclusions: EUCAST RAST at eighth hour will be beneficial in urgent patients due to their high CA rate, easy preparation, inexpensive, and could be performed with the available equipment and personnel.