Unfortunately, when laboratory methods rely solely on cultivation of pathogens and traditional phenotypic methods of pathogen
characterization, physicians are forced to deduce the presence of BSI based on clinical symptoms, which are often nonspecific.
Subsequently, antibiotic therapy is initiated based on clinical and epidemiologic profiles (28) rather than on laboratory evidence. Typically, within 1 to 3 days a microscopic Gram stain category (Gram-positive bacteria,
Gram-negative bacteria, or fungi) provides physicians with a general direction for antibiotic therapy. Definitive results
that eliminate the need for broad-spectrum therapy and enable de-escalation and the tailoring of treatment to the most effective
antibiotic regimen often require more than 3 to 5 days. This gap has been implicated as one reason for high mortality and
the emergence of drug-resistant microbes.