Recolonization of Mutans Streptococci after Application of Chlorhexidine Gel

Streptococcus mutans is specifically suppressed by intensive treatment with chlorhexidine gel, but the time for recolonization and the effect on other oral bacteria are not totally clear. In this study, recolonization of mutans streptococci was evaluated in nine healthy adult volunteers, who were highly colonized with this microorganism. Stimulated saliva was collected before (baseline) and at 1, 7, 14, 21 and 28 days after application of 1% chlorhexidine gel on volunteers' teeth for two consecutive days. On each day, the gel was applied using disposable trays for 3 x 5 min with intervals of 5 min between each application. Saliva was plated on blood agar to determine total microorganisms (TM); on mitis salivarius agar to determine total streptococci (TS) and on mitis salivarius agar plus bacitracin to determine mutans streptococci (MS). Chlorhexidine was capable of reducing the counts of MS and the proportion of MS with regard to total microorganisms (%MS/TM) (p<0.05), but these values did not differ statistically from baseline (p>0.05) after 14 days for MS and 21 days for %MS/TM. The counts of TM and TS and the proportion of MS to total streptococci did not differ statistically from baseline (p>0.05) after chlorhexidine treatment. The results suggest that the effect of chlorhexidine gel treatment on suppression of mutans streptococci is limited to less than a month in highly colonized individuals.

Streptococcus mutans é especificamente suprimido pelo tratamento intensivo com clorexidina em gel, mas o tempo de recolonização e o efeito em outras bactérias orais não está totalmente claro. Nesse estudo, a recolonização de estreptococos do grupo mutans foi avaliado em nove voluntários adultos saudáveis, os quais eram altamente colonizados por esse microrganismo. Saliva estimulada foi coletada antes (baseline) e 1, 7, 14, 21 e 28 dias após a aplicação de clorexidina em gel a 1% nos dentes dos voluntários por dois dias consecutivos. Em cada dia, o gel foi aplicado utilizando moldeiras descartáveis por 3 x 5 min com intervalos de 5 min entre cada aplicação. A saliva foi inoculada em ágar sangue para determinação dos microrganismos totais (MT); em mitis salivarius ágar para determinação dos estreptococos totais (ET) e em meio mitis salivarius com bacitracina para determinar a contagem de estreptococos do grupo mutans (EGM). O tratamento com clorexidina foi capaz de reduzir as contagens de EGM e a proporção de EGM em relação aos microrganismos totais (%EGM/MT) (p<0,05), mas esses valores não diferiram estatisticamente do baseline (p>0,05) após 14 dias para EGM e 21 dias para %EGM/MT. As contagens de MT e ET e a proporção de EGM em relação a estreptococos totais não difereriram estatisticamente do baseline (p>0,05) após o tratamento com clorexidina. Os resultados sugerem que o efeito do tratamento com clorexidina em gel na supressão de estreptococos do grupo mutans é limitado a menos de um mês em indivíduos altamente colonizados. .

Chronic mild stress decreases survival, but not proliferation, of new-born cells in adult rat hippocampus

New-born cells continue to proliferate and survive to become mature granule cells in adult rat hippocampus. Although this process, known as neurogenesis, is inhibited by acute stress, it is not clear whether chronic stress affects neurogenesis. To determine whether chronic mild stress (CMS) influences neurogenesis in the adult rat hippocampus, male Sprague-Dawley rats were exposed to CMS and administered bromodeoxyuridine (BrdU) before or after CMS to observe the survival/differentiation or proliferation of new-born cells, respectively. In addition, we measured brain-derived neurotrophic factor (BDNF) mRNA in the granule cell layer (GCL) of the hippocampus, because BDNF is known to play an important role in the survival of new-born cells. CMS significantly decreased the survival of newborn cells in the GCL, but did not influence the proliferation or differentiation of new-born cells. CMS did not affect the proliferation and survival of new-born cells in the hilus. In addition, CMS did not change BDNF mRNA levels in the GCL. These results demonstrate that CMS reduces the survival of new-born cells but not of their proliferation, suggesting that repeated mild stress could influence a part of neurogenesis, but not the whole part of neurogenesis. These results raise the possibility that the survival of new-born cells may be suppressed in the presence of normal BDNF mRNA levels in GCL.