Families share everything—including Streptococcus mutans, the bacteria most frequently associated with dental caries. Yet research from the University of Alabama at Birmingham (UAB) shows that kids acquire S. mutans from sources outside their families as well.
Children typically have more than one strain or genotype of S mutans, and most share at least one of these strains with their mother or another member of the family. However, 72% of the children in the study had one or more S mutans strains not found in participating members of the household, indicating that these strains came from outside the home.
“While the prevailing theory on S mutans transmission suggests mother-to-child transmission as the primary route of infection, in this study 40% of children shared no strains with their mothers,” said Stephanie Momeni, a doctoral candidate in the UAB department of biology.
According to the study, 22.8% shared 37 strains only with another child in the household such as siblings or cousins, demonstrating another dimension to inter-familiar transmission. Of the children that did not share strains with any household members, 33% were found to have only one isolate, indicating these strains to be rare or transient.
This suggests about one third of strains analyzed might not be clinically relevant and can confound the search for strains related to the disease. It also suggests these strains are highly transmissible but might not become established strains due to bacterial competition or host immune factors.
The study evaluated isolated S mutans from 119 African-American children with at least one household family member. Also, the study evaluated more than one member of the family for 76% of these children. According to UAB, it was a strong study since it evaluated interacting children as well as all participating residential household family members, including extended family.
The researchers determined strain types using a bacterial typing method known as repetitive extragenic palindromic PCR (rep-PCR). For each rep-PCR genotype, children were evaluated as either sharing or not sharing the strain with any household members. Since children in this study had between one and 9 genotypes, the researchers evaluated 315 genotype cases.
“While the data supports that S mutans is often acquired through mother-to-child interactions, the current study illuminates the importance of child-to-child acquisition of S mutans strains and the need to consider these routes of transmission in dental caries risk assessments, prevention, and treatment strategies,” said Momeni.
The researchers say further analysis with an alternate bacterial typing method is needed to confirm these findings. Also, they note that not all household members chose to participate in the study. Momeni presented her research at the American Society for Microbiology MICROBE Meeting in Boston on June 17. The National Institute of Dental and Craniofacial Research provided funding for the project.