2572. The Impact of Antibiotics on the Composition of the Vaginal Microbiota

BACKGROUND: The impact of antibiotics on the composition of the vaginal microbiota (VMB) is poorly defined. We analyzed the VMB of women before and after the use of antibiotics. METHODS: We used samples from a cohort of reproductive-aged women who submitted vaginal swabs and clinical data over a 2-year period. 16S rRNA gene sequencing was conducted, and VMB was categorized into 7 community state types (CSTs): four dominated by Lactobacillus spp. and three low in Lactobacillus, dominated by Streptococcus spp. (CST VI), Bifidobacterium spp. (CST VII), or comprising a variety of anaerobes (CST IV). CSTs were further categorized as Lactobacillus-dominated (LD) or non-Lactobacillus-dominated (NLD). We compared paired vaginal samples collected within 48 hours prior to and 48 hours after completion of antibiotics in 40 women (N = 10 systemic metronidazole, N = 6 vaginal metronidazole, N = 5 trimethoprim-sulfamethoxazole, N = 9 amoxicillin, N = 5 azithromycin, N = 5 other), to time-matched samples in 56 controls. Exact logistic regression was used to evaluate the impact of antibiotics on LD status controlling for baseline CST, race, menses, and hormonal contraceptive use. RESULTS: Women who received antibiotics were 25 times more likely to be in an LD state after antibiotics compared with those who did not receive antibiotics (p = 0.0017). NLD to LD transitions occurred almost exclusively in patients receiving metronidazole. Of 13 women who began in NLD (N = 12 in CST IV) and then received metronidazole, 84.6% (N = 11) transitioned to LD (CST III, L. iners-dominated). Of 7 women who started in an NLD state and received non-nitroimidazole antibiotics, only two (receiving clindamycin or amoxicillin) transitioned to an LD state. None of the 20 women who began in a LD state transitioned to a non-LD state after antibiotics. 12 controls were in an NLD state at baseline, of these 11 remained NLD at the second time point. 44 controls started in an LD state and all remained in LD at the second time point. CONCLUSION: In the short term, metronidazole results in a transition of the VMB from a NLD to a L. iners-dominated state. There was little impact of non-nitroimidazole antibiotics on the VMB. Studies assessing longer-term impact of antibiotics on the composition of the VMB are needed. DISCLOSURES: All authors: No reported disclosures.