DEVELOPMENT AND EVALUATION OF OPTICAL SENSORS FOR THE DETECTION OF BACTERIA

The detection of actively metabolizing microorganisms is performed by many institutions, including medical and public health laboratories as well as quality-assurance departments in the food, cosmetic and pharmaceutical industries. Our objective is to develop a system with: (1) culture bottles containing growth media and sterilizable optical sensors and (2) an instrument that would automatically monitor bottles and evaluate each for evidence of bacterial growth. Carbon dioxide optical sensors have been chosen for the system, since CO2 is recognized as a universal by-product of bacterial metabolism. Fluorimetric sensors, similar in principle to those described previously for measuring PCO2 levels in blood, have been developed and optimized. An instrument (AVL BDS-240) has also been developed. The BDS-240 is a noninvasive automated system for the rapid detection of aerobic and anaerobic bacteria as well as some fungi. The instrument and bottle system are optimized to detect the presence of bacteria and fungi in fresh human blood (blood cultures). The instrument is capable of storing a total of 240 culture bottles. The bottles are arranged in six racks, each of which holds up to 40 bottles. Racks are continuously heated at 35-degrees-C and are agitated for the maximum recovery of organisms. Samples are drawn from patients and injected directly into the culture bottles. The culture bottle is placed into a rack station. Each station has its own LED/photodiode optical unit. Every ten minutes LEDs (two racks at a time) illuminate the optical sensors in the bottles and photodetector measurements from each station are stored and evaluated for significant changes. Those bottles that indicate significant rate increases in CO2 are flagged as positive. In recent clinical evaluation, five hospitals collected approximately 10 000 blood specimens in duplicate and inoculated each specimen into four bottles. Fifty percent of these bottles have been tested by the hospital's existing blood-culture method and the other 50% tested with the AVL BDS-240 system. The clinical trials lasted approximately eight months and the BDS-240 has been found to be equivalent to the hospital's current method with regard to the isolation of relevant microorganisms. However, because of the continuous monitoring capability, microorganisms are detected much faster by the BDS-240. In addition, the AVL system is much less labor intensive than the current methods of the hospitals.