Featured Research

from universities, journals, and other organizations

Salmonella: Trickier Than We Imagined

Date:
June 15, 2008
Source:
University of Rochester Medical Center
Summary:
Salmonella is serving up a surprise not only for tomato lovers around the country but also for scientists who study the rod-shaped bacterium that causes misery for millions of people. Researchers have identified a molecular trick that may explain part of the bacteria's fierceness: A protein allows the bacteria to maintain a low profile in the body, giving Salmonella crucial time to gain a foothold before the immune system is roused to fight the invader.

This scanning electron micrograph (SEM) depicts four highly magnified rod-shaped, motile, Gram-negative Salmonella infantis bacteria, which are attached.
Credit: Janice Carr

Salmonella is serving up a surprise not only for tomato lovers around the country but also for scientists who study the rod-shaped bacterium that causes misery for millions of people.

Related Articles


In research published June 4 in the online journal PloS One, researchers say they've identified a molecular trick that may explain part of the bacteria's fierceness. A team from the University of Rochester Medical Center has identified a protein that allows the bacteria to maintain a low profile in the body, giving the bacteria crucial time to quietly gain a foothold in an organism before the immune system is roused to fight the invader.

"Inflammation immediately after a bacterial infection occurs helps the body fight off bugs like Salmonella quickly," said Jun Sun, Ph.D., the leader of the team and assistant professor of Gastroenterology and Hepatology. "But it may be that Salmonella is especially equipped with tools to allow it to evade the immune system early on, growing quietly and then really making the host quite ill. Salmonella is trickier than we imagined."

Sun's team found that a virulence protein known as AvrA dampens the inflammatory response. That helps the bacteria avoid the wrath of the immune system and gives the infection crucial time to grow and develop before it needs to expend energy to fight off immune cells like neutrophils, which would attack the intruder more quickly if the bacteria attacked the body in a more clear-cut fashion.

"AvrA allows Salmonella to make peace with you, buying the bacteria a little time to survive in the body," said Sun. "That's bad news for the body, because then the bacteria spreads. AvrA allows the bacteria to do harm in the body without the body realizing it. Bacteria have been evolving for millions of years. That gives them some tricks that perhaps we don't understand yet."

AvrA is one of several proteins in Salmonella that affect cells in the wall of the intestines and stomach known as epithelial cells. These cells link up tightly together thanks to molecules known as tight junction proteins, which form an elaborate barrier to keep molecules and substances in or out of the colon. The bacterium employs several proteins enabling it to loosen these junctions, effectively breaking up the barrier and making the body vulnerable to the infection.

While several of Salmonella's proteins allow it to loosen up and punch through this latticework, Sun's team unexpectedly found that AvrA allows the bacteria to maintain these tight junctions. This ability reduces the body's inflammatory response and allows the bacteria to avoid detection by the immune system for some time, enabling the bacteria to survive in the host. The severe symptoms of infection, including nausea, vomiting, diarrhea, and abdominal cramps, typically hit anywhere from 8 to 72 hours after initial exposure to the bug.

"It's a surprising finding, which is why we've repeated our studies many times and done tests in different experimental models," said Sun, whose team studied the phenomenon in the laboratory, in mice, and in cultured human cells.

AvrA is one of several virulence proteins that Salmonella has at its disposal, using syringe-like molecular machinery to shoot toxins and proteins into cells just seconds after its first encounter with a cell in the small or large intestine. The protein is especially adept at functioning in low-acid locales like the gut and bears close resemblance to a virulence protein known as YopJ that is active in Yersinia -- the bug that caused the Black Plague.

Sun is one of several scientists who have shown that AvrA reduces inflammation in the body, acting to some degree like new arthritis medications by reducing the activity of an inflammatory molecule known as NF-Kappa B.

There are thousands of types of the bug. Sun studied Salmonella Typhimurium, one of the two most common types; that bacterium and Salmonella enteritidis together cause more than half the Salmonella illnesses seen in people. While the current outbreak in tomato involves a much more rare form, Salmonella saintpaul, Sun says that the AvrA gene is in more than 80 percent of Salmonella types overall, including the "saintpaul" variety.

Other researchers working on the project, which was funded by the National Institute of Diabetes and Digestive and Kidney Diseases, include Anne Liao, Yun Zhao, and Yinglin Xia of the University of Rochester; Elaine Petrof of Queen's University in Kingston, Ontario; and Erika Claud of the University of Chicago.


Story Source:

The above story is based on materials provided by University of Rochester Medical Center. Note: Materials may be edited for content and length.


Cite This Page:

University of Rochester Medical Center. "Salmonella: Trickier Than We Imagined." ScienceDaily. ScienceDaily, 15 June 2008. <www.sciencedaily.com/releases/2008/06/080613104801.htm>.
University of Rochester Medical Center. (2008, June 15). Salmonella: Trickier Than We Imagined. ScienceDaily. Retrieved November 26, 2014 from www.sciencedaily.com/releases/2008/06/080613104801.htm
University of Rochester Medical Center. "Salmonella: Trickier Than We Imagined." ScienceDaily. www.sciencedaily.com/releases/2008/06/080613104801.htm (accessed November 26, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Wednesday, November 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

From Popcorn To Vending Snacks: FDA Ups Calorie Count Rules

From Popcorn To Vending Snacks: FDA Ups Calorie Count Rules

Newsy (Nov. 25, 2014) The US FDA is announcing new calorie rules on Tuesday that will require everywhere from theaters to vending machines to include calorie counts. Video provided by Newsy
Powered by NewsLook.com
Feast Your Eyes: Lamb Chop Sent Into Space from UK

Feast Your Eyes: Lamb Chop Sent Into Space from UK

Reuters - Light News Video Online (Nov. 25, 2014) Take a stab at this -- stunt video shows a lamb chop's journey from an east London restaurant over 30 kilometers into space. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Cambodian Capital's Only Working Elephant to Retire in Jungle

Cambodian Capital's Only Working Elephant to Retire in Jungle

AFP (Nov. 25, 2014) Phnom Penh's only working elephant was blessed by a crowd of chanting Buddhist monks Tuesday as she prepared for a life of comfortable jungle retirement after three decades of giving rides to tourists. Duration: 00:36 Video provided by AFP
Powered by NewsLook.com
Stray Dog Follows Adventure Racing Team for 6-Day Endurance Race

Stray Dog Follows Adventure Racing Team for 6-Day Endurance Race

Buzz60 (Nov. 24, 2014) A Swedish Adventure racing team travels to try and win a world title, but comes home with something way better: a stray dog that joined the team for much of the grueling 430-mile race. Jen Markham has the story. Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins