Which is the anaerobic bacteria that is commonly found in cervix or vagina which keeps the pH low and protect from other bacterial infections?

Lactobacillus or Doderlein's bacillus is the most common organism found in vagina. Lactobacilli are gram-positive non-spore-forming rods found as members of the normal flora in the mouth, colon, and female genital tract. In the mouth, they may play a role in the production of dental caries. In the vagina, they are the main source of lactic acid, which keeps the pH low. Ref: Levinson W. (2012). Chapter 27. Minor Bacterial Pathogens. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.