This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
The protective bacterium in the normal vagina is: 
Select and explain. 
A. Peptostreptococcus, B. Lactobacillus, C. Gardenella vaginalis, D. E. coli
B: Lactobacillus
Answer: B: Lactobacillus 
Explanation: Vagina has inhabitant bacteria called as Doderleins bacteria which is a lactobaccilli, and converts the glycogen present in vaginal epithelium into lactic acid.
Thus, pH of the vagina is acidic
The pH of the vagina in an adult woman is 4 -5.5 with an average of 4.5.
The pH of vagina varies with age — for further details see preceding text.