Study: Certain Gut Bacteria May Influence Susceptibility to Infection

19 Aug 2014 --- The specific composition of bacterial species in a person's gut may protect against or increase susceptibility to Campylobacter, the most common cause of human bacterial intestinal inflammation, according research published this week in mBio, the online open-access journal of the American Society for Microbiology. The study also found that Campylobacter infection can yield lasting changes to one's gut bacteria composition.

"It has been known for a long time that the microbiota, or microorganisms in the gut, can protect a person from colonization by organisms that cause intestinal tract disease. However, very little is known about how human gut microbiota influences susceptibility to these organisms, and to Campylobacter in particular," said senior study author Hilpi Rautelin, MD, PhD, professor of clinical bacteriology at Uppsala University and Uppsala University Hospital in Sweden. "We wanted to see if the composition of the human gut microbiota plays a role in susceptibility to Campylobacter infection."

Rautelin and colleagues followed 24 workers at three poultry slaughterhouses in Sweden. In 2010, they collected fecal samples from the workers once a month from June to September, during the summer peak of Campylobacter-positive chicken flocks, and again the following February. Fecal samples were cultured for Campylobacter and analyzed by sequencing for all bacteria. While all participants tested negative for Campylobacter at the beginning of the study, seven participants became culture positive for the organism during the study. Only one of the Campylobacter-positive participants experienced symptoms of illness.

Those who became Campylobacter-positive had a significantly higher abundance of Bacteroides and Escherichia organisms than those who remained culture negative, suggesting that these bacterial species likely play an important role in colonization resistance. This group also had a significantly higher abundance of Phascolarctobacterium and Streptococcus species than those in the Campylobacter-negative group, which had an overrepresentation of Clostridiales, unclassified Lachnospiraceae, and Anaerovorax species.

"Elevated proportions of Bacteroides and Escherichia species in the gut microbiota may predispose humans to Campylobacter infection," Rautelin said. "These particular species have been shown to have an important role for susceptibility to gut pathogens and Campylobacter in particular in some mouse model studies."

Following the individuals' fecal microbiota compositions over time, the researchers observed that the Campylobacter-negative individuals had small differences but those who tested positive for Campylobacter showed significant changes by the February sample. Researchers do not yet know the implications of these changes, Rautelin said.

Whether microbiota composition alone or together with an individual's immune status also plays a significant role in the eradication of Campylobacter from the intestines remains to be studied, she said.