464: Quantitative PCR: a useful tool for assessing vaginal bacterial load

ObjectiveAntibiotic (Abx) treatment of bacterial vaginosis (BV) does not reduce the risk of preterm birth (PTB). Methods of quantifying the change in the bacterial load post-treatment have been limited. We sought to determine whether quantitative PCR is a valid method to assess vaginal bacterial load.Study DesignWe utilized stored vaginal samples from a prior trial in which women were randomized in the midtrimester to either azithromycin and metronidazole or placebo to examine the effect on PTB. All women had risk factors for PTB including: 1) positive fetal fibronectin, 2) BV (Nugent score 7-10) and a prior PTB or 3) BV and a prepregnancy weight <50kg. Vaginal bacterial loads were measured using quantitative PCR for 16S rRNA. Bacterial loads were compared pre- and post-treatment with the rank sum test and correlated with Nugent scores (0-10). Individual patient differences were examined with the paired sign rank test.Results238 paired vaginal samples were available for pre- and post-treatment analysis: 119 in the Abx group and 119 in the placebo group. Treatment groups did not differ by risk factors for PTB. Baseline bacterial load did not differ by treatment group (p=0.87). Post-treatment microbial load was significantly lower in the Abx group compared to placebo (p=0.0017). In the BV subgroup, results were similar (p=0.0006). Individual patient bacterial load decreased significantly post-treatment in the Abx group (<0.0001), but not in the placebo group; findings were similar for those with BV (p<0.0001). Despite this microbial load decrease in the Abx group, the rate of PTB < 37 weeks did not decrease (p=0.24). For all samples, microbial load was correlated with Nugent score and each of its specific bacterial components (Mobiluncus hominis, Gardnerella vaginalis, and Lactobacillus sp.) (Table).Tabled 1Correlation between Nugent score and microbial loadConclusionQuantitative PCR reflects decreased bacterial load after Abx treatment and correlates with Nugent score. This new tool may allow us to better understand the vaginal microbiota and explain the relationship between BV and PTB. ObjectiveAntibiotic (Abx) treatment of bacterial vaginosis (BV) does not reduce the risk of preterm birth (PTB). Methods of quantifying the change in the bacterial load post-treatment have been limited. We sought to determine whether quantitative PCR is a valid method to assess vaginal bacterial load. Antibiotic (Abx) treatment of bacterial vaginosis (BV) does not reduce the risk of preterm birth (PTB). Methods of quantifying the change in the bacterial load post-treatment have been limited. We sought to determine whether quantitative PCR is a valid method to assess vaginal bacterial load. Study DesignWe utilized stored vaginal samples from a prior trial in which women were randomized in the midtrimester to either azithromycin and metronidazole or placebo to examine the effect on PTB. All women had risk factors for PTB including: 1) positive fetal fibronectin, 2) BV (Nugent score 7-10) and a prior PTB or 3) BV and a prepregnancy weight <50kg. Vaginal bacterial loads were measured using quantitative PCR for 16S rRNA. Bacterial loads were compared pre- and post-treatment with the rank sum test and correlated with Nugent scores (0-10). Individual patient differences were examined with the paired sign rank test. We utilized stored vaginal samples from a prior trial in which women were randomized in the midtrimester to either azithromycin and metronidazole or placebo to examine the effect on PTB. All women had risk factors for PTB including: 1) positive fetal fibronectin, 2) BV (Nugent score 7-10) and a prior PTB or 3) BV and a prepregnancy weight <50kg. Vaginal bacterial loads were measured using quantitative PCR for 16S rRNA. Bacterial loads were compared pre- and post-treatment with the rank sum test and correlated with Nugent scores (0-10). Individual patient differences were examined with the paired sign rank test. Results238 paired vaginal samples were available for pre- and post-treatment analysis: 119 in the Abx group and 119 in the placebo group. Treatment groups did not differ by risk factors for PTB. Baseline bacterial load did not differ by treatment group (p=0.87). Post-treatment microbial load was significantly lower in the Abx group compared to placebo (p=0.0017). In the BV subgroup, results were similar (p=0.0006). Individual patient bacterial load decreased significantly post-treatment in the Abx group (<0.0001), but not in the placebo group; findings were similar for those with BV (p<0.0001). Despite this microbial load decrease in the Abx group, the rate of PTB < 37 weeks did not decrease (p=0.24). For all samples, microbial load was correlated with Nugent score and each of its specific bacterial components (Mobiluncus hominis, Gardnerella vaginalis, and Lactobacillus sp.) (Table).Tabled 1Correlation between Nugent score and microbial load 238 paired vaginal samples were available for pre- and post-treatment analysis: 119 in the Abx group and 119 in the placebo group. Treatment groups did not differ by risk factors for PTB. Baseline bacterial load did not differ by treatment group (p=0.87). Post-treatment microbial load was significantly lower in the Abx group compared to placebo (p=0.0017). In the BV subgroup, results were similar (p=0.0006). Individual patient bacterial load decreased significantly post-treatment in the Abx group (<0.0001), but not in the placebo group; findings were similar for those with BV (p<0.0001). Despite this microbial load decrease in the Abx group, the rate of PTB < 37 weeks did not decrease (p=0.24). For all samples, microbial load was correlated with Nugent score and each of its specific bacterial components (Mobiluncus hominis, Gardnerella vaginalis, and Lactobacillus sp.) (Table). ConclusionQuantitative PCR reflects decreased bacterial load after Abx treatment and correlates with Nugent score. This new tool may allow us to better understand the vaginal microbiota and explain the relationship between BV and PTB. Quantitative PCR reflects decreased bacterial load after Abx treatment and correlates with Nugent score. This new tool may allow us to better understand the vaginal microbiota and explain the relationship between BV and PTB.