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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.

Experiments were done to examine the sensitivity of various waterborne bacteria from iodinated systems to iodine, and their subsequent recovery and growth, because this halogen is used as a disinfectant in potable water systems on US manned space vehicles. A Pseudomonas aeruginosa isolated from a commercial iodine product was least sensitive when grown in reagent-grade water or phosphate buffered water (PBW) and most sensitive when cultivated on mineral salts medium supplemented with low levels of glucose and glutamate or Brain Heart Infusion (BHI) broth. However, a P. cepacia strain was most sensitive when grown on BHI broth. Isolates from an iodinated potable water system were less sensitive to iodine than Ps-4 while a clinical isolate exhibited intermediate sensitivity. Bacteria including Ps-4 generally recovered and grew in PBW at greater rates than uniodinated controls.