Humidity fattens chance for detection

FEB. 11–BERKELEY, Calif.–Researchers have determined that the spores of an anthrax cousin swell by a significant amount as humidity increases, a surprsing discovery that could lead to a rapid way of detecting anthrax.

The researchers, from the University of California, Berkeley, and the Children’s Hospital Oakland Research Institute, had been examining size differences between spores of different strains of Bacillus bacteria. While checking the spores’ reaction to different environmental conditions, such as humidity, they found the change in size.

After anthrax spores were sent through the mail in the fall of 2001, the researchers decided to examine the spores of Bacillus thuringiensis, bacteria related to the deadly organism.

As reported Feb. 10 in the Proceedings of the National Academy of Sciences, lead researcher Andrew Westphal and colleagues, using a powerful microscope, were able to record the swelling of B. thuringiensis spores. Under high humidity, the spores, whose diameter is a fraction of the width of a human hair, puffed out by 4 percent.

“We found something unexpected to biologists,” Westphal told United Press International. “Biologists tend to think of spores as inert things that don’t respond to the environment. We obtained the cousins of anthrax to see if we could tell the difference between different types of spores just based on size, which people hadn’t done.”

If spores of different strains show characteristic swelling patterns, their unique responses to the environment could be the key to developing fast biosensors, the researchers said. Such sensors could identify anthrax spores while ignoring background dust and other particles that do not react to humidity.

Current pathogen detection devices rely on sweeping filters through the air and sending them to a lab, with turnaround times ranging between 12 and 24 hours.

If the new findings can be translated into a physical detection system, the waiting time could be reduced to 10 minutes, the researchers said.

Westphal, a physicist at Berkeley’s space sciences laboratory, says the team should have more definitive answers within the next few months.

Buford Price, Berkeley physics professor and co-author of the paper, indicated that one possible application of the sensing technology, once developed, would be to detect anthrax or other microbes at post offices.

“One could examine every single letter,” Price says. If a particle fingerprint matched that of anthrax or another biological agent, a specialist would be called to the site to verify whether a threat exists, he adds.

Westphal and Price agreed the study results also could help biodefense experts improve microbe decontamination practices. For example, Westphal explained, the new data shed light on why decontamination of anthrax was more effective under wetter conditions.

Under humid conditions, Price says the spores swell and “nanometer-size pores get bigger and allow (decontaminating) gases to go in.”

Although “this is probably great science,” the nation still needs a broader, more comprehensive strategy to defend itself against a biological attack, says Dr. Tara O’Toole, director of the Johns Hopkins Center for Civilian Biodefense Strategies in Baltimore.

“We’re spending too much on detection and not enough on response,” O’Toole said, noting detection is getting the lion’s share of funding.

Without a good response strategy, which O’Toole said the government does not have, detection will not help fight an attack.

“When talking about attacks against civilians, are we going to put detectors in every room, every building?” O’Toole asked, adding, “If we detect (a microbe) but can’t do anything about it, (detection) is no good.”


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