Both oral probiotics and douching supplementation can prevent and cure vaginitis and vaginosis. An interesting study on probiotics and vaginosis was conducted in a 2007 by the University of Milan (Drago et al).
They found that after a 6 day daily douche of Lactobacillus acidophilus and Lactobacillus paracasei F19, 92.5% of women had their vaginosis cured. The fishy order was cured in all women. The pH levels of women were normalized to 4.5 in 34 out of 40 women.
Probiotics has also been shown to reduce mastisis.