Distribution of Genomic Island TnSmu2 Genes among Streptococcus mutans Isolates

S. mutans is considered to be a principal cause of dental caries. S. mutans is quite diverse at the genetic level; genomic islands acquired by horizontal transfer are a major source of variation. However, the population distribution and role of genes located on these islands have not been described.

Objectives: Confirm and compare the occurrence of genes located in the TnSmu2 genomic island, identified in the S. mutans UA159 genome, among ~ 500 clinical isolates of S. mutans from 3-4 year-old children.

Methods: Plaque samples were collected from 200 pre-school children enrolled in Eastern Iowa Head Start and WIC Programs and their parents. S. mutans was isolated following a sequential selective/differential plating scheme, biochemical assays, and final identity confirmed via PCR using S. mutans-specific probes. Genomic S. mutans DNA was extracted from each isolate and printed on a single Library on a Slide (LOS) microarray. We selected 24 ORFs from TnSmu2 for screening based on appropriate size and known/proposed function. A fluorescein gene probe was created by amplifying DNA from UA159 using PCR. Labeled probes were hybridized to the LOS microarray to determine gene prevalence. We used TIGR software for image extraction and analysis, and SAS for statistical analysis.

Results: To date, 16/24 probes have been hybridized against the LOS microarray. Two were present in all isolates, and 14 occurred in a similar pattern and frequency in 70% of the isolates.

Conclusions: By the high throughput LOS microarray approach, genes found in the genomic island TnSmu2 occurred widely among ~500 S. mutans isolates, and the gene content was relatively stable across strains. This stability may indicate that TnSmu2 genes are functionally important in S. mutans. Future analyses will evaluate the association of these genes with caries status in these children. Supported by R01-DE014899 and R21-DE015008.