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Drinking water aboard spacecraft and on earth must be monitored to ensure that harmful bacteria are absent. NASA needs rapid methods for this purpose, to avoid possible launch delays and limit potential water-related health risks aboard spacecraft on orbit. Determination of bacterial viability after exposure to disinfection has significant health importance since oxidatively injured pathogenic bacteria have been shown to retain their virulence. This problem is compounded by the observation that injured bacteria are recovered at significantly lower frequencies using standard agar plate assays, leading to an underestimation of infection risks. Escherichia coli O157:H7 was exposed to 0.5 ppm free chlorine, retained on membrane filters and tested for physiological activity using a variety of assays.

To compare the disinfection susceptibility of mucoid and non-mucoid P. aeruginosa in relation to EPS production, cultures were grown to stationary phase in defined media with a high or low C/N ratio using glucose as carbon source. Cultures diluted with phosphate buffered water pH 7.2 were pretreated by vortexing, centrifuging, or blending with 10 mM EDTA in PBW before disinfection with iodine, chlorine or monochloramine. It is suggested that differences observed between disinfectants may be due to their reactivities with cell constituents or modes of action. EPS may play a significant role in bacterial resistance to iodine and other halogens, although susceptibility varies markedly in relation to nutrient status and sample treatment before disinfection.

To determine the microbiological quality of water for potable and other purposes, there is a need for rapid methods to enumerate viable bacteria. This is of particular importance for the proposed water recovery systems planned for the United States Space Station, in which wastewaters including hygiene water and urine will be reclaimed for potable use. Existing microbiological culture methods are limited by the time taken to obtain results and because it is not possible to detect the total microbial populations by these methods. We have been investigating direct microscopic methods which detect individual bacterial cells. Fluorogenic compounds are used which are taken up by active cells, permitting a direct assessment of physiological activity. The methods are being adapted for use with membrane filtration which permits concentration of small numbers of cells from large volumes of water. Procedures for direct examination of cells growing on surfaces as biofilms have also been devised.