Water comes clean with new purity test.

Water from a pristine mountain spring may be fine to drink, but it's not clean enough for drug and computer-chip manufacturers. Both need huge amounts of ultrapure water, which is filtered so clean that it contains only one or two bacteria in a liter of liquid.

Researchers from Organo Corp. and Fuji Electric Corporate Research and Development in Japan have developed a new, quick way to detect bacteria in ultrapure water, down to individual cells. Using this method, the group finds that contamination in ultrapure water is much higher than existing tests show.

The pharmaceutical industry uses ultrapure water in sterile products such as intravenous solutions. In computer-chip manufacturing, ultrapure water flushes away chemicals between processing steps. Stray particles could bridge the tiny connections etched onto the chip, causing a short circuit.

"The microelectronic requirements are even more demanding than the pharmaceutical requirements," says Theodore H. Meltzer, a water-filtration consultant in Bethesda, Md. Because one organism can multiply, "you can't be casual about even the lowest amounts."

Up until now, the best way to determine bacterial contamination has been to pass a water sample through an ultrafine filter, grow any captured cells for 2 to 7 days, and then count the number of colonies that form. This process is slow and "inadequate in terms of selectivity and sensitivity," says microbiologist Marc Mittelman of Altran Corp., an engineering firm in Boston. The Japanese group's method improves on all these aspects, he notes.

The researchers created a novel probe for bacteria by using antibodies that attach themselves to any DNA they come across. These antibodies were derived from mice genetically engineered to model the autoimmune disease lupus. When the antibodies are attached to an enzyme that catalyzes a light-producing chemical reaction, the complex glows in the presence of DNA.

To assess contamination, the researchers capture bacteria on a filter, break the cells apart to release their DNA, then apply the probe. A sensitive camera records the tiny spots of light from the filter, the team reports in the Dec. 15, 1998 ANALYTICAL CHEMISTRY.

The new technique detected up to 225 times more cells in ultrapure water than the traditional technique did, at least in part because the method counts dead bacteria as welt as living ones. Chip makers can use this information, since even dead cells can cause a short circuit. Pharmaceutical companies, however, would need additional tests to distinguish between live and dead organisms, Mittelman says.