Food safety microbiologist battles food-borne pathogen

WEST LAFAYETTE, Ind. - Arun Bhunia's (pronounced Ah-rhun Boone-ya) early interest in animal diseases led him naturally to research, which has expanded into developing tiny sensors designed to detect dangerous bacteria, a realm of science he never fathomed when growing up on a farm in India.

For the past 12 years Bhunia, Purdue University associate professor of food science, has delved into the workings of the deadliest of food-borne pathogens, Listeria monocytogenes, looking for ways to detect and prevent it from causing illness. The bacteria are responsible for approximately 2,500 cases of disease annually in the United States with a fatality rate of 20 percent, according to the Centers for Disease Control and Prevention.

His research, which also may enable him someday to develop a vaccine or other prevention for food-borne illness, has earned him the 2003 Agriculture Research Award from the Purdue School of Agriculture. During the presentation on Friday, April 18, Bhunia will give a seminar on his work, entitled "Exploiting Pathogenic Signatures of Listeria monocytogenes for the Development of Biosensor-based Detection Tools."

Although Listeria is relatively rare, the fact that it kills so many of its victims and can grow almost anywhere, including in the refrigerator, makes fast, accurate detection of the pathogen of vital importance. Bhunia, who received his doctorate in 1989, has spent nearly his entire career studying Listeria. He is now applying his microbiology expertise to collaborations aimed at developing biochip sensors for finding and identifying virulent Listeria and other pathogens.

Randy Woodson, director of Purdue's Office of Agricultural Research Programs, said that Bhunia's research is vital because current methods of detecting food contaminants are too slow, and that means dangerous bacteria may reach consumers' tables.

"A rapid testing system would ensure that food containing harmful bacteria is detected before it enters the food chain," Woodson said. "Arun is willing to use his knowledge of the organism's basic biology to work with other researchers, such as engineers, to develop new tools."

When Bhunia arrived at Purdue in August 1998, he joined forces with other researchers in the Department of Food Science and the departments of Agricultural and Biological Engineering and Electrical and Computer Engineering to develop contaminant detection methods.

"I realized from a microbiology standpoint you could only reach a certain level in detection methods," Bhunia said. "For instance, if you have high numbers of bacteria from food, they can be detected without using engineering tools. But when you have low numbers, microbiologically, we cannot do it in a short time period."

This is especially important since it takes just 100 to 1,000 Listeria cells to make someone sick. Bhunia realized that to develop a sensitive, rapid detection system he would need to be familiar with a whole new language – engineering. The engineers also learned from him because Bhunia understood the workings of the bacteria, how small they are and how rapidly they could become dangerous.

"We've educated each other so we could be productive," he said.

When Bhunia was doing his postdoctoral work, his main project was to develop antibodies for Listeria, which led to immunologic assays, or tests, to identify the bacteria. From this, he found a line of mouse cells that would die when exposed to a pathogenic form of Listeria. The cells would remain viable if the bacteria weren't infectious.

He has refined this method so that the assay can identify virulent Listeria in one hour. Bhunia is using the assay to better understand how Listeria kills cells and also to aid a collaborative effort to develop a detection system that can be used in a farm field, a processing plant or a store. Researchers also may develop sensors for identifying other contaminants.

Bhunia now has a line of cells that could be placed on a biochip. When a dangerous form of Listeria is introduced, it will bind to the healthy cells on the chip. If this happens, the sensor will give a signal that the virulent pathogen is present.

Bhunia currently has three major areas of study. One is to find a way to keep the cells used for detection alive long enough so such a biochip will be feasible for practical use. A second is to make the detection system sensitive enough to detect and identify the pathogen even if only a few of the bacterium are present. A third is to understand how Listeria adheres, or binds, to intestinal wall cells, allowing it to cause disease.

"What I want to achieve is if we have 10 bacterial cells attacking one mammalian cell, and the cell dies because of that interaction, we are able to measure that with the biosensor," Bhunia said. "I suspect it shouldn't take more than 20 minutes or 30 minutes for detection to take place."

Having a system that not only detects the bacteria but also tells whether it is pathogenic and does it quickly with a small food sample is imperative for a biochip to be meaningful in the field, he said.

Bhunia's dedication to finding practical applications for his work is one reason he and his research are being honored, Woodson said.

"While he's really intrigued by the basic biology of an organism, he wants to see his understanding of that biology translated into solutions to real-world problems," Woodson said. "He's done that at a very early stage in his career."

Bhunia is taking his research even further than just detecting Listeria. He wants to understand how the bacteria make people sick.

"This is basic medical research, but it's giving us a lot of applied information that complements our detection strategy because it is directly related to how the bacteria interacts with the cells we want to put on the biochip," Bhunia said.

Eventually he hopes to try a genetic method of preventing Listeria from binding to the cells in the intestine so that the infection can't occur in humans.

Bhunia grew up in the state of West Bengal near Calcutta, India. He earned his bachelor's degree in veterinary medicine in 1984 at Krishi Viswa Vidyalaya, an agriculture university in India. He earned his doctorate at the University of Wyoming in 1989.

The Agricultural Research Award is given annually to a Purdue School of Agriculture scientist who has completed a doctoral degree within the past 15 years. The recipient is chosen on the basis of research excellence and contributions made to agriculture, natural resources and the quality of life for Indiana citizens.

The honoree receives $1,000, which is funded by the Charles Gutherie Patterson Memorial Endowment and the Matthew Morgan Hamilton Fund. In addition, $5,000 is awarded to support the recipient's research.

Bhunia has received research funding from the U.S. Department of Agriculture's Agricultural Research Service, the Purdue Center for Food Safety Engineering and the National Cattlemen's Beef Association.

Writer: Susan A. Steeves

http://news.uns.purdue.edu/hp/Bhunia.agaward.html