Detection of microbial invasion of the amniotic cavity by analysis of cervicovaginal proteins in women with preterm labor and intact membranes.

OBJECTIVE: Microbial invasion of the amniotic cavity (MIAC) is common in early preterm labor and is associated with maternal and neonatal infectious morbidity. MIAC is usually occult and is reliably detected only with amniocentesis. We sought to develop a noninvasive test to predict MIAC based on protein biomarkers in cervicovaginal fluid (CVF) in a cohort of women with preterm labor (phase 1) and to validate the test in an independent cohort (phase 2). STUDY DESIGN: This was a prospective study of women with preterm labor who had amniocentesis to screen for MIAC. MIAC was defined by positive culture and/or 16S ribosomal DNA results. Nine candidate CVF proteins were analyzed by enzyme-linked immunosorbent assay. Logistic regression was used to identify combinations of up to 3 proteins that could accurately classify the phase 1 cohort (N = 108) into those with or without MIAC. The best models, selected by area under the curve (AUC) of the receiver operating characteristic curve in phase 1, included various combinations of interleukin (IL)-6, chemokine (C-X-C motif) ligand 1 (CXCL1), alpha fetoprotein, and insulin-like growth factor binding protein-1. Model performance was then tested in the phase 2 cohort (N = 306). RESULTS: MIAC was present in 15% of cases in phase 1 and 9% in phase 2. A 3-marker CVF model using IL-6 plus CXCL1 plus insulin-like growth factor binding protein-1 had AUC 0.87 in phase 1 and 0.78 in phase 2. Two-marker models using IL-6 plus CXCL1 or alpha fetoprotein plus CXCL1 performed similarly in phase 2 (AUC 0.78 and 0.75, respectively), but were not superior to CVF IL-6 alone (AUC 0.80). A cutoff value of CVF IL-6 ≥463 pg/mL (which had 81% sensitivity in phase 1) predicted MIAC in phase 2 with sensitivity 79%, specificity 78%, positive predictive value 38%, and negative predictive value 97%. CONCLUSION: High levels of IL-6 in CVF are strongly associated with MIAC. If developed into a bedside test or rapid laboratory assay, cervicovaginal IL-6 might be useful in selecting patients in whom the probability of MIAC is high enough to warrant amniocentesis or transfer to a higher level of care. Such a test might also guide selection of potential subjects for treatment trials.

Azorhizobium caulinodans pyruvate dehydrogenase activity is dispensable for aerobic but required for microaerobic growth.

Azorhizobium caulinodans mutant 62004 carries a null allele of pdhB, encoding the E1beta subunit of pyruvate dehydrogenase, which converts pyruvate to acetyl-CoA. This pdhB mutant completely lacks pyruvate oxidation activities yet grows aerobically on C(4) dicarboxylates (succinate, L-malate) as sole energy source, albeit slowly, and displays pleiotropic growth defects consistent with physiological acetyl-CoA limitation. Temperature-sensitive (ts), conditional-lethal derivatives of the pdhB mutant lack (methyl)malonate semialdehyde dehydrogenase activity, which thus also allows L-malate conversion to acetyl-CoA. The pdhB mutant remains able to fix N(2) in aerobic culture, but is unable to fix N(2) in symbiosis with host Sesbania rostrata plants and cannot grow microaerobically. In culture, A. caulinodans wild-type can use acetate, beta-D-hydroxybutyrate and nicotinate--all direct precursors of acetyl-CoA--as sole C and energy source for aerobic, but not microaerobic growth. Paradoxically, acetyl-CoA is thus a required intermediate for microaerobic oxidative energy transduction while not itself oxidized. Accordingly, A. caulinodans energy transduction under aerobic and microaerobic conditions is qualitatively different.