Direct disk diffusion test during bacteremia : evaluation of antibiotic susceptibility results

Introduction: Bacteremia are emergencies that are life threatening to patients. Early initiation of adequate antibiotic therapy reduces mortality and morbidity. The purpose of this work was to evaluate the results obtained with the direct AST, carried out directly from positive blood cultures on Mueller-Hinton CHROMagar medium (CHROMagar 4, place du 18 Juin 1940 - 75006 Paris, France) and compare them with those obtained with the standard AST. Methods: To do this, 124 strains isolated from 124 bottles were tested against 21 antibiotics. The resulting diameters were read after 8h and 18h of incubation, interpreted using the CLSI breakpoints and compared to those obtained with the standard method. Results: It was found that, the results were extremely satisfactory at 18h (94.43% CA, 0.24% ME and 0.00% VME), compared to less conclusive results at 8h (87.32% CA). The best %CA were obtained with gentamicin, sulfamethoxazole+trimethoprim, levofloxacin, ampicillin and cefoxitin at 8h (all >93%) and 18h (all >97%). Also, non-fermenting GNB recorded the best results with 98.74%CA at 18h and Staphylococcus species the lowest ones with 90.70% CA at 18h. Conclusion: The encouraging results obtained during the present study suggest a possible future implementation of the direct-from-bloodculture AST as a routine technique. However, the standard AST remains the reference technique.