College of Letters and Science honors students gathered in the State Street Room of the UCen last night to listen as Professor Michael J Mahan of the Molecular, Cellular and Developmental Biology department gave a lecture outlining his research on potentially detrimental strains of salmonella and ongoing efforts to develop a vaccine that will combat them.

Hosted by the UCSB Honors Association, the event featured the research of Mahan and other researchers, who completed a study on stains of ‘hypervirulent’ salmonella bacteria in conjunction with researchers at UC Davis and The University of Sydney, Australia. The research team recently published their findings on two hypervirulent strains of salmonella, a bacterial disease that is the leading common cause of foodborne illness in the United States. The strains, S. choleraesuis and S. bovismorbificans, are able to escape detection because they are unresponsive in the laboratory setting and only activate once inside an animal.

Since the strains of disease are internalized, Mahan said the greatest obstacle in performing research was actually detecting the strains.

“This is why it’s a big problem — we don’t know it’s there,” Mahan said.

Hypervirulent strains also override all current forms of vaccination and while immunizations protect against 20 strains of salmonella, they are not effective against what Mahan termed “superstrains.”

Salmonella, once contracted through oral ingestion, first deacidifies the stomach and inflames the small intestine. Then it deactivates immune cells called macrophages, progresses to the blood and finally causes ulceration of the intestines and organ failure. While it initially decreases proinflammatory and proinhibitory immune responses, it later induces a significant proinflammatory response that causes immune cells to swell up like “giant balloons,” Mahan said.

Mahan, who first began studying the disease as an undergraduate student, said his younger brother’s personal battle with salmonella inspired him to perform such research.

“He had it for a couple years. It went right in his bones and stunted his growth,” Mahan said. “I just never liked it. Now I like it but in a different way. I get to figure stuff out.”

The researchers first studied salmonella in pigs, but they became more attuned to the existence of the hypervirulent strains with news of outbreaks occurring on Australian ships carrying 100,000 sheep each to countries in the Eastern Hemisphere. Unlike normal strains, they remain latent for three days but then exhibit increased colonization and are particularly deadly.

Reasearchers are now directing their efforts at determining what causes hypervirulent strains to activate inside the cell, according to Mahan.

“Once we understand those switches we can incorporate that into our vaccine,” Mahan said.

Some students expressed intrigue at the concept of inactive and active states of the strains, such as first-year biology major Lauren Dykman, who said the talk shone light on the environments of emerging disease strains.

“I thought it was interesting how salmonella would switch depending on the surrounding environment,” Dykman said.

Calla Martyn, president of the Letters and Science Honors Association and a third-year biology major, said events such as yesterday’s lecture fulfill the club’s primary goal of facilitating closer contact between students and faculty members.

“We want to let students meet informally with faculty members and be exposed to a variety of subjects, especially by professors who are really passionate about their subject,” Martyn said.

Such events also provide honors students with the opportunity to meet each other, as they oftentimes do not get the chance to meet peers who are also in the College of Letters and Science Honors Program.


Molecular, cellular and developmental biology professor Michael T. Mahan lectured yesterday about his research involving two undetectable salmonella strains. Professor Mahan’s current research involves how these strains activate within cells.