More than 200,000 cases of bacteremia occur each year in
the United States (3). Fungemia, although less common, is
increasingly important as a complication of immunosuppressive
therapy and disorders of immunity. Because of the
serious morbidity and mortality associated with bacteremia
and fungemia and the wide variety of microorganisms involved,
the rapid, accurate, and reliable detection of these
conditions is one of the most challenging problems in clinical
microbiology. Many systems have been developed to recover
microorganisms from blood and other body fluids, but
each has certain limitations. Manual systems are simple to
use and do not require additional instrumentation, but they
rely upon visual inspection and blind subculturing to detect
microorganisms and thus require repeated manipulation of
the bottles. Semiautomated systems eliminate the need for
blind subcultures but still require repeated manipulations
and also require additional instrumentation (2). In addition,
both manual and semiautomated systems are traditionally
inspected or tested only once or twice daily, which may limit
their ability to detect microorganisms at the earliest possible
time.
In this paper, we describe a new automated microbial
detection system designed to overcome many of the limitations
of manual and semiautomated systems. We present
data gathered during development of the instrument that
demonstrate the principle of the system and its ability to
support and detect growth in a timely manner and data from
a limited pilot clinical trial that compared a prototype
research instrument with the radiometric BACTEC 460
system (Becton Dickinson Diagnostic Instrument Systems,
Towson, Md.).
MATERIALS AND METHODS
Description of the prototype BacT/Alert system. (i) Media.
Two different broth media were evaluated: one for growing
common aerobic, microaerophilic, and fastidious bacteria
and common yeasts and the other for growing anaerobic
bacteria. The proprietary media are based on a tryptic soy
broth supplemented with complex amino acids and carbohydrates
and are designed both to support growth and to ensure
optimal C02 production. Both bottle types contain 30 ml of