Matrix-Assisted Laser Desorption Ionization–Time-of-Flight Mass Spectrometry with Time-of-Flight Peak Analysis for Rapid and Accurate Detection of Group B Streptococcus in Pregnant Women

Severe infections in neonates caused by Streptococcus agalactiae, Group B Streptococcus (GBS), are often associated with GBS transmission from their mothers during labor or birth. Hence, it is necessary to develop a universal method for screening vaginal–rectal GBS colonization in pregnant women worldwide. A subculture of vaginal–rectal swabs using a selective enrichment broth and an agar plate is conventionally recommended for GBS screening. However, infants born to mothers who are GBS negative on subculture sometimes contract GBS infections. Therefore, we developed another method with high sensitivity for GBS screening. A total of 178 vaginal–rectal swabs from pregnant women were inoculated into the enrichment broth, of which 126 were suspected of containing GBS due to the change in the color of the broth. The subculture results were positive for GBS in 34 (27.0%) swabs. Each broth was then analyzed using matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI-TOF MS). Analysis of the TOF peaks specific to GBS revealed 45 (35.7%) swabs as GBS positive. Of the 11 GBS positive samples on TOF peak analysis but negative on subculture, S. agalactiae gene targets were detected through PCR in 4 samples. MALDI detection with analysis of peaks of TOF (MDAPT) can detect GBS directly from cultured broth with high sensitivity. MDAPT can be an alternative method for GBS screening in pregnant women and contribute to the prevention of severe GBS infectious diseases in neonates. IMPORTANCE As previously reported, 10%–30% of pregnant women carry Streptococcus agalactiae, Group B Streptococcus (GBS), in their vagina or rectum, and approximately 50% of them vertically transmit GBS to their neonates during labor or birth. Moreover, 1%–2% of the GBS-transmitted neonates develop severe GBS infectious diseases, which have a mortality rate of 19.2% in a preterm infant and 2.1% in a full-term infant. Hence, universal screening for GBS colonization in pregnant women is conducted worldwide using the subculture procedure; however, infants born to GBS negative mothers sometimes contract GBS infections. Therefore, other laboratory techniques are required for detecting GBS more accurately. The proposed method “MALDI detection with analysis of peaks of TOF (MDAPT)” detects GBS directly from cultured broth with high sensitivity. Therefore, it can be an alternative method for GBS screening in pregnant women, thereby contributing to the prevention of severe GBS infectious diseases in neonates.