Intervention: Metronidazole
Trial phase: Phase 2
ATC code: A01AB17 | A02BD01 | A02BD02 | A02BD03 | A02BD08 | A02BD11 | A02BD13 | A02BD15 | D06BX01 | G01AF01 | G01AF20 | J01RA03 | J01RA04 | J01RA10 | J01RA14 | J01XD01 | P01AB01 | P01AB51 | P01AB52
SMILES: Cc1ncc([N+](=O)[O-])n1CCO
Sex: Female
Age groups: Adult
Healthy volunteers: No
Participants at risk: 151
Group description: 5-day course of metronidazole gel 7.5 mg/gm daily applied vaginally, then LACTIN-V 2x10^9 cfu/dose applied vaginally for 5 days then twice weekly for 10 weeks.
Eligibility criteria:
Inclusion Criteria:

1. Capable of reading and writing English and voluntarily provide written informed consent to participate in the study and comply with all study procedures 2. Untreated BV (asymptomatic or symptomatic) as diagnosed during the screening visit defined by >/=3 Amsel criteria. Note: Amsel criteria include the following: --Homogeneous, thin, grayish-white discharge that smoothly coats the vaginal walls; --Vaginal pH >4.5; --Positive whiff-amine test, defined as the presence of a fishy odor when a drop of 10% potassium hydroxide (KOH) is added to a sample of vaginal discharge; --Presence of clue cells (>20% on microscopy). 3. Untreated BV(asymptomatic or symptomatic) as confirmed in the laboratory using the Nugent scoring system (Nugent Score >/= 4) 4. Otherwise healthy pre-menopausal women 18-45 years of age on the day of screening 5. Regular predictable menstrual cycles or amenorrheic for at least 3 months due to use of a long-acting progestin or continuous use of oral contraceptives 6. Willing to be asked questions about personal medical health and sexual history. 7. Willing to apply study agent vaginally and comply with study examinations. 8. Agree to abstain from sexual intercourse during the first 5 consecutive days of study product administration, 12 hours prior to study visits and for 12 hours after each study product application 9. Agree to abstain from the use of any other intravaginal product throughout the trial period from the time of screening through Visit 7 (Week 24, Day 168) Note: Intravaginal products include contraceptive creams such as Gynol II, gels, foams, sponges, lubricants not approved by the study investigators, and douches. Limit use of tampons during menstruation to unscented products. 10. Must be of non-childbearing potential or if of childbearing potential, must agree to use a reliable method of birth control for the duration of the study Note: Reliable methods of birth control include tubal ligation, male partner with a vasectomy, a steroidal contraceptive (oral, patch, injectable or implantable), IUD, condoms or abstinence.

Exclusion Criteria:

1. Urogenital infection at screening Note: Urogenital infection includes urinary tract infection, Trichomonas (T.) vaginalis, Neisseria (N.) gonorrhoeae, Chlamydia (C.) trachomatis, Treponema (T.) pallidum, or vulvo-vaginal candidiasis. 2. Diagnosis of two or more outbreaks of N. gonorrhoeae, C. trachomatis, T. pallidum, T. vaginalis, or herpes simplex virus (herpes genitalis) within 6 months prior to screening 3. Positive for syphilis or HIV at screening 4. Current pregnancy or within 2 months of last pregnancy and/or currently breastfeeding**. Criteria will be assessed at screening and enrollment. 5. Vaginal or systemic antibiotic or antifungal therapy (other than MetroGel given as part of study procedures) within 21 days of screening or within 30 days of enrollment** 6. Use of disulfiram within past 2 weeks or other contraindication to use of MetroGel** 7. Any condition requiring regular periodic use of systemic antibiotics during participation in the trial 8. Active genital herpes lesion** (if not resolved by enrollment)** 9. Investigational drug use other than LACTIN-V within 30 days or 10 half-lives of the drug, whichever is longer, of enrollment visit** 10. Other planned participation in an investigational drug study while participating in this study** 11. Menopause defined as more than 12 consecutive months of amenorrhea without another known cause including pregnancy 12. IUD insertion or removal, pelvic surgery, cervical cryotherapy or cervical laser treatment within the last 2 months prior to screening 13. Use of vaginal ring (eg, NuvaRing) within 3 days of screening or during the course of the study** 14. Failure to complete 5 days of MetroGel with the last dose taken no later than 48 hours prior to randomization*** 15. Use of new long-acting hormonal treatments. Participant may be enrolled if stable (>3 months) on existing therapy as determined by the principal investigator** 16. Known allergy to any component of LACTIN-V/placebo or MetroGel or to nitroimidazole derivatives or latex (condoms) 17. Any social, medical, or psychiatric condition, including history of drug or alcohol abuse that in the opinion of the investigator would make it unlikely for the participant to comply with the study ** Note: Criteria will be assessed at screening and enrollment. ***Note: Criteria will be assessed at enrollment