Molecular-based Screening for Perinatal Group B Streptococcal Infection: Implications for Prevention and Therapy

Abstract

Group B streptococci (GBS) are a leading cause of infectious neonatal morbidity and mortality. Timely and accurate identification of colonized pregnant women is imperative to implement intrapartum antibioprophylaxis (IAP) to reduce the risk of early neonatal sepsis. Current guidelines recommend screening for GBS carriage with vaginal-rectal cultures. However, cultures require 24-72 h, thus precluding their use for intrapartum screening and these are only performed at 35-37 weeks gestation. New rapid molecular-based tests can detect GBS within hours. They have the potential to be used intrapartum and to allow for selective IAP in women carrying GBS. An advantage is that they can sometimes be performed by non-laboratory staff in the labor suite, thus avoiding delays in sample transfers to the microbiology laboratory. Another possible use of molecular-based assays is for the diagnosis of neonatal sepsis, where tests with a short turnaround time and high sensitivity and specificity are crucial. In this situation, the detection of microorganisms once antibiotic therapy has already been started is important, as treatment is started immediately once sepsis is suspected without waiting for microbiological confirmation. In this article, we discuss the state-of-the-art molecular-based tests available for GBS screening during pregnancy, as well as their implications for IAP for the diagnosis and prevention of neonatal sepsis.

Development of a melting-curve based multiplex real-time PCR assay for simultaneous detection of Streptococcus agalactiae and genes encoding resistance to macrolides and lincosamides

“…Real-time PCR is one of the rapid and feasible methods for maternal intrapartum GBS screening, and most of the in house and commercial tests are based on the utilization of probes [ 29 , 36 – 41 ]. In this study, a sensitive melting curve-based multiplex real-time PCR was designed and evaluated for simultaneous detection of GBS and the most prevalent macrolide and lincosamide resistance markers.…”

“…Several real-time PCR-based assays have been developed in the last decades for GBS detection in vaginal-rectal swab from pregnant women [ 29 , 36 – 41 ]. Most of these studies target the cfb gene for specific detection of GBS [ 8 , 29 , 37 ].…”

“…Several real-time PCR-based assays have been developed in the last decades for GBS detection in vaginal-rectal swab from pregnant women [ 29 , 36 – 41 ]. Most of these studies target the cfb gene for specific detection of GBS [ 8 , 29 , 37 ]. However, the following genes were also used for GBS detection by real-time PCR assays: those of the operon dlt [ 37 , 38 ], which catalyze the incorporation of D-alanine residues into GBS cell wall lipoteichoic acids [ 44 ]; cyl B [ 39 ], which encodes a transmembrane protein of ABC transporter required for the production of GBS hemolysin [ 45 ]; ssr A [ 40 ], encoding tmRNA involved in the degradation of truncated proteins [ 46 ]; and sip [ 41 ], encoding a surface immunogenic protein [ 47 ].…”

“…In general, nucleic acid amplification tests (NAAT) have been proven highly specific and with higher sensitive (reported sensitivity range of 86 to 100%) for detection of GBS vaginal-rectal colonization compared to the conventional culture-based test [ 8 , 29 , 36 , 50 ]. This difference can be due to the presence of both non-viable cells or GBS antagonistic microorganisms [ 51 ].…”

“…The cfb gene encodes an extracellular pore-forming protein [ 26 ] known as CAMP (acronym for Christie, Atkins and Munch-Peterson) factor [ 27 ], which has been widely used for phenotypic identification of GBS isolates [ 28 ]. Furthermore, most nucleic acid amplification tests (including commercially available ones) target cfb gene for detection of GBS vaginal-rectal colonization [ 29 ]. The potential usefulness of the assay was evaluated for prenatal GBS screening in vaginal-rectal swab specimens.…”