Evaluation of a direct method for the identification and antibiotic susceptibility assessment of microrganisms isolated from blood cultures by automatic systems

The purpose of blood cultures in the septic patient is to address a correct therapeutic approach. Identification and antibiotic susceptibility test carried out directly from the bottle may give important information in short time.The introduction of the automatic instrumentation has improved the discovering of pathogens in the blood, however the elapsing time between the positive detection and the microbiological report is still along. Is the evaluation of this study a fast, easy, cheap method to be applied to the routine, which could reduce the response time in the bacteraemia diagnosis.The automatic systems Vitek Senior (bioMérieux), and Vitek 2 (bioMérieux) were used at Pio Albergo Trivulzio (Centre1) and at Istituto dei Tumori (Centre2) respectivetly.To remove blood cells, 7 ml. of the culture has been moved by vacuum sampling in a test tube and centrifuged for 10 minutes at 1000 rpm the supernatant has been further centrifuged for 10 minutes at 3000 rpm.0.5 ml. of BHI has been added to the pellet o sediment.The concentration of bacterial suspension has been fit for the inoculation. At the same time has been prepared standard cultures in suitable culture media were carried out for comparison. In the centro1 and centro2 have been isolated and identify respectively 63 and 31 Gram negative, and, 32 and 40 gram positive microorganisms have been isolated and identify in the Centre1 and Centre2 respectively.The identification Gram-negative and Gram positive microorganisms showed an agreement of 100% and 86.2% and 93.3% and 65.78% respectively between the direct and the standard method. For antibiotic susceptibility tests, 903 (Centre1) and 491 (Centre2) and 396 and 509 compounds were totally assessed in Gram negative and Gram positive bacteria respectively.The analysis has highlighted that: Centre1 has reported 0.30% very major errors (GE), 0.92% major errors (EM), 1.23% minor errors (Em). Centre 2 showed 0.57% very major errors (GE), 0.09% major errors (EM), 1.34% minor errors (Em).The low percentage of GE of EM and Em obtained, the low cost and impact in the laboratory routine justify the use of a direct method with automatic instrumentations so that it allows to set up in short times an addressed antibiotic therapy.