Can male ejaculation cause vaginal bacteria infection?

Here are some ... Semen can transmit STDs such as HIV, Hep-B & C, trichomonas but not bacterial vaginitis. However, sexual intercourse can bring the existing bacteria into vagina. Fortunately, the wonder of Nature / God imbeds females with strong defense mechanism to make the brought-in bacteria unable to survive but sperms to survive for fertilizing the waiting egg, except a few.
Infxn is fm bacteria. Its not the ejaculate but during sex it is possible to transmit bacteria and diseases.The ejaculate itself comes from deep w/i the male body so its sterile.Anytime 2 people have sex there is always a risk of an STD.So try to have both partners shower before and a/f sex.The acidity of the vagina will naturally control bacteria.If there are signs of infection: persistent odor,discharge, etc see a MD.
Absolutely. In short, yes! Now, the bacteria can either be abnormal growth of your own bacteria, or one can get a bacterial sexually transmitted infection. Semen is alkaline and the vaginal environment is acidic, so pH changes can shift the growth of your bodies own flora, especially if there is a larger volume of ejaculate. To find out what type of bacteria are present you need a pelvic exam. Hope this helps.