ArcR modulates biofilm formation in the dental plaque colonizer Streptococcus gordonii.

Biofilm formation and cell-cell sensing by the pioneer dental plaque colonizer Streptococcus gordonii are dependent upon arginine. This study aimed to identify genetic factors linking arginine-dependent responses and biofilm formation in S. gordonii. Isogenic mutants disrupted in genes required for the biosynthesis or catabolism of arginine, or for arginine-dependent gene regulation, were screened for their ability to form biofilms in a static culture model. Biofilm formation by a knockout mutant of arcR, encoding an arginine-dependent regulator of transcription, was reduced to < 50% that of the wild-type whereas other strains were unaffected. Complementation of S. gordonii ∆arcR with a plasmid-borne copy of arcR restored the ability to develop biofilms. By DNA microarray analysis, 25 genes were differentially regulated in S. gordonii ∆arcR compared with wild-type under arginine-replete conditions including eight genes encoding components of phosphotransferase systems for sugar uptake. By contrast, disruption of argR or ahrC genes, which encode paralogous arginine-dependent regulators, each resulted in significant changes in the expression of more than 100 genes. Disruption of a gene encoding a putative extracellular protein that was strongly regulated in S. gordonii ∆arcR had a minor impact on biofilm formation. We hypothesize that genes regulated by ArcR form a critical pathway linking arginine sensing to biofilm formation in S. gordonii. Further elucidation of this pathway may provide new targets for the control of dental plaque formation by inhibiting biofilm formation by a key pioneer colonizer of tooth surfaces.

Prevalence of sub-clinical vitamin A deficiency in 2-5-year-old children in Tehran.

To determine vitamin A status using conjunctival impression cytology (CIC) in children aged 2-5 years, we assessed 1257 randomly selected children in urban and rural areas of Tehran. History of using supplemental vitamin A, respiratory or diarrhoeal infection in the previous 6 months, residential location, parents' education, family economic status, and child's age, sex and weight were recorded. Sub-clinical vitamin A deficiency (defined as abnormal CIC) was found in 23.6% of the sample, a rate classified as a moderate public health problem. There was a statistically significant relationship between sex and age and abnormal CIC (P < 0.05).

A Critical Role for Extracellular DNA in Dental Plaque Formation.

Extracellular DNA (eDNA) has been identified in the matrix of many different monospecies biofilms in vitro, including some of those produced by oral bacteria. In many cases, eDNA stabilizes the structure of monospecies biofilms. Here, the authors aimed to determine whether eDNA is an important component of natural, mixed-species oral biofilms, such as plaque on natural teeth or dental implants. To visualize eDNA in oral biofilms, approaches for fluorescently stained eDNA with either anti-DNA antibodies or an ultrasensitive cell-impermeant dye, YOYO-1, were first developed using Enterococcus faecalis, an organism that has previously been shown to produce extensive eDNA structures within biofilms. Oral biofilms were modelled as in vitro "microcosms" on glass coverslips inoculated with the natural microbial population of human saliva and cultured statically in artificial saliva medium. Using antibodies and YOYO-1, eDNA was found to be distributed throughout microcosm biofilms, and was particularly abundant in the immediate vicinity of cells. Similar arrangements of eDNA were detected in biofilms on crowns and overdenture abutments of dental implants that had been recovered from patients during the restorative phase of treatment, and in subgingival dental plaque of periodontitis patients, indicating that eDNA is a common component of natural oral biofilms. In model oral biofilms, treatment with a DNA-degrading enzyme, NucB from Bacillus licheniformis, strongly inhibited the accumulation of biofilms. The bacterial species diversity was significantly reduced by treatment with NucB and particularly strong reductions were observed in the abundance of anaerobic, proteolytic bacteria such as Peptostreptococcus, Porphyromonas and Prevotella. Preformed biofilms were not significantly reduced by NucB treatment, indicating that eDNA is more important or more exposed during the early stages of biofilm formation. Overall, these data demonstrate that dental plaque eDNA is potentially an important target for oral biofilm control.

Prevalence of sub-clinical vitamin A deficiency in 2-5-year-old children in Tehran

To determine vitamin A status using conjunctival impression cytology [CIC] in children aged 2- 5 years, we assessed 1257 randomly selected children in urban and rural areas of Tehran. History of using supplemental vitamin A, respiratory or diarrhoeal infection in the previous 6 months, residential location, parents' education, family economic status, and child's age, sex and weight were recorded. Sub- clinical vitamin A deficiency [defined as abnormal CIC] was found in 23.6% of the sample, a rate classified as a moderate public health problem. There was a statistically significant relationship, between sex and age and abnormal CIC [P < 0.05]