Development of a Rapid PCR Assay for Screening of Maternal Colonization by Group B Streptococcus and Neonatal Invasive Escherichia coli during Labor

Abstract

Objective: Group B Streptococcus (GBS) and Escherichiacoli(E. coli) are the leading causes of early-onset neonatal disease (EOD). Intrapartum antibiotic prophylaxis of GBS-colonized women decreases vertical transmission and EOD due to GBS. Nevertheless, no intervention has been developed to reduce the risk of EOD related to E. coli. Timely and accurate identification of colonized mothers is necessary to implement preventive strategies against neonatal sepsis. To screen for colonization during labor, we developed a real-time PCR assay for the simultaneous detection of GBS and neonatal invasive strains of E. coli. Study Design: Specific DNA targets for GBS are publicly available. For neonatal invasive E. coli, we analyzed candidate DNA targets by DNA hybridization on microarrays of invasive strains isolated from neonatal E. coli sepsis or meningitis (K1 and not K1 ‘invasive’ serotypes). Specificity of DNA probes was tested against a panel of bacteria and by simulating clinical conditions (spiking vaginal samples from pregnant women). Then, the characteristics of the selected probes were evaluated in a pilot study including 200 women in labor. Results: Prevalence of rectovaginal GBS and of vaginal and cervical E. coliserotype K1 colonization were 16.0, 3.5 and 3.5% by culture and 27, 10 and 8.5% by PCR, respectively. The prevalence of other invasive E. coli in the vagina and in the cervix, detected by PCR, was around 10%. Compared to the culture, considered as the gold standard, the sensitivities of the PCRs for the GBS and E. coli K1 were 97 and 71%, respectively. Specificities were 86 and 92%, respectively. Specificity is difficult to interpret, as a false-positive PCR result may in fact be a false-negative result of the culture. The turnaround time needed for PCR analysis was 2.5 h, compared to a minimum of 48 h for the culture. Conclusion: Our rapid PCR is reliable in detecting GBS in women in labor. Optimization of the PCR for invasive E. coli is needed before its implementation in clinical practice. More efforts to fight against main causes of neonatal sepsis need to be undertaken to prevent this terrible medical complication.