Colonization with mutans streptococci and lactobacilli and the caries experience of children after the age of five.

Some authors suggest that there is a "window of infectivity" for mutans streptococci (MS) at an early age, after which colonization is not likely to occur. Moreover, children with low or non-detectable levels of MS at an early age are at lower risk for caries. It was our aim to study caries experience and colonization with MS and lactobacilli in a group of children at 11 years of age who had been documented to have been MS-free until 5 years of age. For this group, the mfs and MFS values at 11 years of age were found to be 1.12+/-2.81 and 0.44+/-0.88, respectively. These values are much lower than those of a control group of 11-year-old children who had always been MS-positive since the age of 2, being 3.10+/-3.43 and 1.20+/-1.91, respectively. Of the 30 children without detectable MS up to the age of 5, 22 had acquired MS at 11 years of age, but their MS counts were significantly lower than those of the control group. No correlation was observed between the levels of MS of the children and the mothers. In children at 11 years of age, no differences were found in the numbers of lactobacilli and sugar intakes per week between the children MS-free and the children MS-colonized at 5 years of age. The present study indicates that the acquisition of MS is still possible after the so-called "window of infectivity" and that a delayed acquisition of MS may reduce the caries experience in the primary and permanent dentition at a later age.

[The new fight against mutant streptococci]. / De nieuwe strijd tegen mutans streptokokken.

Mutans streptococci are an important factor in the aetiology of dental caries. New ways of combating these bacteria have become available with the development of molecular biological techniques. One of these strategies involves the genetic modification of mutans streptococci to develop less cariogenic mutants. Acid production and the production of intracellular polysaccharides have been eliminated. But it is not clear yet whether these less cariogenic mutant strains are able to replace the normal mutans streptococci in dental plaque. Immunization is another possibility to suppress mutans streptococci. Antibodies against proteins involved in adherence of mutans streptococci have been raised by active immunization. It is also possible to raise antibodies in cow serum and milk, in eggs of chickens and even in tobacco plants. After isolation, these antibodies are to be applied topically. In the future, these new strategies may prevent or reduce caries. However, further research is necessary to resolve the obstacles on the way to commercial application.

Nitroreduction and formation of hemoglobin adducts in rats with a human intestinal microflora.

In the covalent binding of nitroarenes to macromolecules, nitroreduction is an important step. The intestinal microflora represents an enormous potential of bacterial nitroreductase activity. As a consequence, the in vivo nitroreduction of orally administered nitroarenes is primarily located in the intestine. In this study, we have investigated the nitroreduction of 2-nitrofluorene (2-NF) by a human microflora in female Wistar rats. Germ-free (GF) rats were equipped with a bacterial flora derived from human feces. Nontreated GF rats and GF animals equipped with a conventional rat flora were used as controls. The composition of the human and the conventional microflora isolated from the rats were consistent with the microflora of the administered feces. In the rats receiving only sunflower seed oil, no adducts were detected. The animals equipped with a human or rat microflora that received 2-aminofluorene (2-AF) formed 2-AF hemoglobin (Hb)-adducts at average levels (mean +/- SEM) of 5.3 +/- 0.3 and 6.7 +/- 0.7 mumole/g Hb, respectively. After 2-NF administration, the adduct levels were 0.022 +/- 0.003 and 0.043 +/- 0.010 mumole/g Hb, respectively. In the GF rats, an adduct level of 0.57 +/- 0.09 was determined after 2-AF administration and no adducts were detected after 2-NF administration. The results show that nitroreduction by an acquired human intestinal microflora and subsequent adduct formation can be studied in the rat in vivo.

Solid-phase extraction and gas chromatographic-mass spectrometric determination after hydrolysis of 2-aminofluorene haemoglobin adducts in blood of rats.

2-Nitrofluorene is an environmental pollutant that binds covalently to haemoglobin after nitroreduction and successive N-hydroxylation. these haemoglobin adducts can be cleaved in vitro by mild base-catalysed hydrolysis. For the enrichment of arylamines from the aqueous hydrolysate, an extraction procedure with an organic solvent is widely used. Because of the formation of a thick emulsion layer between the aqueous and organic solvent layers, the extraction is laborious and inefficient. The use of Amberlite XAD2 provides a simple extraction procedure yielding a recovery of ca. 70%. Calibration curves in haemoglobin solution were prepared with a correlation coefficient of 0.998 (n = 12). The inter-day coefficient of variation amounted to 14%.