NASA-Marshall Space Flight Center (MSFC) has an interest in an automated in-line monitor that can detect the presence of microbial contamination in recovered water. Ideally, this system should also be able to identify and enumerate the microbial contaminant. The Viable Microbial Monitor (VM2) is based on conductance microbiology which depends on the well documented ability of microorganisms to change the electrochemical properties of their growth medium during incubation. The VM2 is intended for the rapid detection of bacterial or fungal contamination in water and other samples.
From October 1992 to July 1993, NASA-MSFC sponsored a Microbial In-line Monitor (MIM) study to evaluate the VM2 for its ability to detect ten microorganism species (9 bacteria and 1 yeast) recovered from Water Recovery Tests (WRT) conducted at MSFC. These WRT isolates may represent the microbes that have potential to contaminate a water recovery system. Three temperatures (30, 35, and 40°C) and three media (m-Plate Count Broth [HPC], 1/2 strength Tryptic Soy Broth [½TSB], and R2A Broth) were used for the evaluation. The final outcome of this study was to select 3 of the 10 microbes for further study.
Results showed that Klebsiella oxytoca, Staphylococcus epidermidis, and Corynebacterium xerosis gave the greatest overall response. Detection time ranged from approximately 5.4 hours (K. oxytoca) to 15.8 hours (C. xerosis). The change in conductance ranged from 143 μSiemens (K. oxytoca) to 20 μSiemens (C. xerosis). For each microbial species selected, reproducible results were obtained more rapidly than that obtained by conventional assays. Significantly different conductance growth patterns were observed which may permit subsequent identification.
Data and graphs representing microbial detection, growth rates, growth patterns, and reproducibility will be presented. In addition, thoughts on future research and applications will be considered.