Helicobacter pylori is one of the most common bacteria that causes infections in people. It is linked to ulcers and cancers of the stomach and intestines, as well as an increased susceptibility to food and waterborne illnesses and malnutrition.
Douglas Berg, a researcher of molecular microbiology at Washington University Medical School, and Robert H. Gilman, a researcher of international health at the Bloomberg School of Public Health at Hopkins, studied whether this pathogen is more likely to be transmitted within families or among unrelated persons.
Their research provides new insights in the quest to control the rates of infection, as well as to determine how H. pylori evolves.
H. pylori is a spiral-shaped bacterium that grows in various areas of the stomach and intestines. It infects the gastric mucosa, the mucous membrane that lines and protects the inside of the stomach.
Although approximately 30 percent of the U.S. population is infected with H. pylori, the greatest rates of infection are seen among the impoverished in developing countries, where it is suspected that they are infected as infants, before being exposed to it continually throughout their lives.
Sixty-two families in the Peruvian shantytown of Las Pampas de San Juan de Miraflores (PSJM) participated in this study, which compared the genetic makeup of H. pylori bacteria among family members, in order to better understand how transmission of this pathogen occurs in developing countries.
H. pylori was initially obtained from participants through use of the string test, which is an alternative to endoscopy. Participants swallowed a gelatin capsule that contained an absorbent cotton string with a protruding end that was taped to the cheek. The string was then withdrawn after 90 minutes and brought to a laboratory for further study.
Bacterial samples were analyzed by a genetic technique called DNA fingerprinting. Because bacteria grow and divide so rapidly, they tend to accumulate small mutations in their DNA. By identifying the genotype at several characteristic mutation sites, scientists can obtain a fingerprint that lets them know which strain of bacteria they are looking at.
Based upon these sequences, 30 percent of strains among mothers and children appeared to be closely related, whereas 70 percent did not. In comparison, 18 percent of strains were identical between a father and his children, 32 percent among siblings and a 25 percent similarity among spouses.
Based upon these results, Berg and Gilman determined that there tended not to be a relationship between strains among family members.
Despite adjusting for factors such as housing characteristics, the location in which families tended to consume their meals and the presence of domestic animals inside houses, sharing a strain was far less common in the shantytown studied than in industrialized societies.
Strains among family members showed a greater relationship than did random strains across the community.
As 70 percent of children's strains in the Peruvian shantytown studied were not closely related to either those of their mother or another family member, most infections in this region tend to be community-acquired: People are infected outside of the home.
Yet the strains of the children did tend to be more closely related to those of a family member than they were to the general community, so it is believed that a significant contributor to developing an infection in PSJM may be familial or other common sources shared among community members.
The majority of PSJM citizens tended to be infected with only one strain of H.pylori. Researchers believe that established strains in any one person have become difficult to displace, or if displacement does occur, it does so rapidly through the use of a superinfecting strain.
If displacement does occur, it tends to do so gradually. Age does not seem to play a factor in this, with the exception of children contracting different strains from adults, as their stomachs tend to have normal levels of acidity.
Since H.pylori appears to be transmitted in the community in developing countries, researchers will be able to apply community-based measures to reduce the prevalence of this pathogen.
