[Obtention of bacterial antibiotic susceptibility following standard conditions directly from infected biological fluids and positive blood cultures].
Determining the conditions, which would allow us to apply bacterial antibiotic susceptibility tests directly to infected biological fluids and positive blood cultures and in accordance with the standard conditions of these tests. For infected fluids (N=23), a correlation was determined between the bacterial count observed by microscopic field on a cystopin centrifugation pellet and the dilution required to obtain bacterial inocula corresponding to those used in the standard antibiogram and E-test methods. For blood cultures detected positive with the BactALERT system (26 Enterobacteriaceae, 29 Staphylococcus and 11 Pneumococcus), the broth dilution required to obtain such inocula was determined for each bacterial type. For infected fluids, the dilution required for the antibiogram of enterobacterial and staphylococcal isolates was respectively of 10(-1) and 10(0) when there were 50 to 100 bacteria/field, 10(-2) and 10(-1) for 100 to 500, 10(-3) and 10(-2) for 500 to 1000, and 10(-4) and 10(-3) for>1000. A minimum of 50 to 100 bacteria/field was required to determine beta-lactam MICs towards a pneumococcal isolate present in cerebrospinal fluid. For blood cultures, a broth dilution of 10(-4) for Enterobacteriaceae and of 10(-2) for Staphylococcus and Pneumococcus allowed to reproduce the standard antibiogram. To reproduce the standard conditions of the E-test method for beta-lactam MICs towards a pneumococcal isolate, the broth dilution was 10(-1). Following the procedure described, antibiotic susceptibility can be available 24 h earlier.