Nav: Home

Mass. General researchers show how Shigella survives the gastrointestinal tract

May 31, 2017

Surviving the treacherous journey through the human body from the mouth to the colon takes a special kind of bacterial pathogen. Shigella - a group of bacteria responsible for much of the diarrheal disease affecting children in the developing world - travels unimpeded from the mouth to the colon, where they unleash powerful machinery to trigger debilitating diarrhea. Researchers from Massachusetts General Hospital (MGH) have been looking not only at how Shigella survives this journey but also how it takes advantage of substances that would kill many less persistent organisms. Each year Shigella is responsible for at least 80 million infections and approximately 700,000 deaths worldwide. Long-term effects for Shigella survivors can include impaired physical and cognitive development, poor gastrointestinal health, reactive arthritis or kidney damage depending on the strain causing infection. Although 99 percent of cases occur in developing nations, approximately half a million occur in the U.S. each year.

To gain important insights into the pathogenesis of Shigella, MGH researchers focused on its mechanisms of virulence and survival as the organism travels to the colon. Among other findings, they determined that Shigella uses multiple mechanisms to survive exposure to bile salts in the small intestine. An essential component of digestion, bile destroys many harmful bacteria, but it cannot disarm intestinal pathogens such as E. coli, Salmonella, Vibrio and Shigella.

"For the first time, we have identified how Shigella not only resists bile but also uses this alkaline fluid produced by the liver to its advantage," says Christina S. Faherty, PhD, of the Mucosal Immunology and Biology Research Center (MIBRC) at MGH, senior author of a paper published in the June issue of Infection and Immunity. "We analyzed how the pathogen's gene expression changes in response to bile salts exposure. The changes we identified pointed to the use of antibiotic resistance mechanisms to resist bile, to the development of a more infectious organism through increased virulence gene expression, and to one better able to survive the colonic environment due to additional gene expression changes." Subsequent mutational analyses confirmed the bile resistance mechanisms of Shigella.

With no current vaccine against Shigella, antibiotics are the only treatment option. But like so many pathogens, Shigella has developed resistance to many antibacterial drugs. "The ability of Shigella to resist antibiotics so efficiently may be partly due to the bacteria's exposure to bile during transit of the small intestine," says Faherty. "It appears that bile primes intestinal pathogens for antibiotic resistance, since many of the same mechanisms used to resist bile exposure are used to resist antimicrobials. Our findings on Shigella's bile resistance mechanisms could have important implications for overcoming multi-drug resistance."

The study also highlighted an additional response of Shigella to bile. Previous work by Faherty and other researchers has shown that two hours of exposure to bile salts increases the ability of Shigella to adhere to and invade epithelial cells lining the gastrointestinal tract. By prolonging the exposure to mimic the time required for Shigella to transit the small intestine, Faherty's current work demonstrated for the first time that longer exposure to bile salts led to the formation of biofilms - communities of bacteria that produce a protective coating to resist harsh environmental conditions.

Faherty believes biofilm formation enables Shigella to clump together to transit through the small intestine. Faherty's team also found that the reabsorption of bile salts that normally takes place in the lower small intestine causes the biofilm to disperse, releasing the hyper-virulent bacteria to infect tissues in the colon. In all, these observations provide a more complete picture of how Shigella transits the small intestine to reach the colon for infection.

An assistant professor of Pediatrics at Harvard Medical School, Faherty is enthusiastic about the study's insights into Shigella pathogenesis and hopes this research could lead to new strategies to combat antibiotic resistance and develop vaccines. "Researchers have been trying to find a successful candidate vaccine to fight Shigella for more than 50 years," she says. "By identifying some of the early mechanisms of how Shigella navigates the intestine and demonstrating how the bacteria use bile as a signal to prepare for infection in the colon, we now have a greater understanding for developing potential new therapies."
-end-
Kourtney P. Nickerson, PhD, postdoctoral fellow at the MGH MIBRC, and Rachael B. Chanin, formerly a technician at MGH and now a graduate student at the University of Texas, Southwestern, are co-first authors. Other collaborators include Jeticia R. Sistrunk and David A. Rasko, PhD, Institute for Genome Sciences, University of Maryland; Peter Fink, MGH MIBRC; Eileen M. Barry, PhD, University of Maryland; and James P. Nataro, MD, PhD, MBA, FAAP, University of Virginia. Support for this work includes National Institute of Allergy and Infectious Diseases grants K22 AI104755, U19 AI110820 and 5T32 AI095190-04.

Massachusetts General Hospital, founded in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH Research Institute (http://www.massgeneral.org/research/about/RI-welcome.aspx) conducts the largest hospital-based research program in the nation, with an annual research budget of more than $800 million and major research centers in HIV/AIDS, cardiovascular research, cancer, computational and integrative biology, cutaneous biology, genomic medicine, medical imaging, neurodegenerative disorders, regenerative medicine, reproductive biology, systems biology, photomedicine and transplantation biology. The MGH topped the 2015 Nature Index list of health care organizations publishing in leading scientific journals and earned the prestigious 2015 Foster G. McGaw Prize for Excellence in Community Service. In August 2016 the MGH was once again named to the Honor Roll in the U.S. News & World Report list of "America's Best Hospitals."

Massachusetts General Hospital

Related Bacteria Articles:

Conducting shell for bacteria
Under anaerobic conditions, certain bacteria can produce electricity. This behavior can be exploited in microbial fuel cells, with a special focus on wastewater treatment schemes.
Controlling bacteria's necessary evil
Until now, scientists have only had a murky understanding of how these relationships arise.
Bacteria take a deadly risk to survive
Bacteria need mutations -- changes in their DNA code -- to survive under difficult circumstances.
How bacteria hunt other bacteria
A bacterial species that hunts other bacteria has attracted interest as a potential antibiotic, but exactly how this predator tracks down its prey has not been clear.
Chlamydia: How bacteria take over control
To survive in human cells, chlamydiae have a lot of tricks in store.
Stress may protect -- at least in bacteria
Antibiotics harm bacteria and stress them. Trimethoprim, an antibiotic, inhibits the growth of the bacterium Escherichia coli and induces a stress response.
'Pulling' bacteria out of blood
Magnets instead of antibiotics could provide a possible new treatment method for blood infection.
New findings detail how beneficial bacteria in the nose suppress pathogenic bacteria
Staphylococcus aureus is a common colonizer of the human body.
Understanding your bacteria
New insight into bacterial cell division could lead to advancements in the fight against harmful bacteria.
Bacteria are individualists
Cells respond differently to lack of nutrients.

Related Bacteria Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Jumpstarting Creativity
Our greatest breakthroughs and triumphs have one thing in common: creativity. But how do you ignite it? And how do you rekindle it? This hour, TED speakers explore ideas on jumpstarting creativity. Guests include economist Tim Harford, producer Helen Marriage, artificial intelligence researcher Steve Engels, and behavioral scientist Marily Oppezzo.
Now Playing: Science for the People

#524 The Human Network
What does a network of humans look like and how does it work? How does information spread? How do decisions and opinions spread? What gets distorted as it moves through the network and why? This week we dig into the ins and outs of human networks with Matthew Jackson, Professor of Economics at Stanford University and author of the book "The Human Network: How Your Social Position Determines Your Power, Beliefs, and Behaviours".