Investigation of Streptococcus agalactiae Colonisation in pregnant women using culture and a novel qPCR Kit

Maternal colonisation with Streptococcus agalactiae (GBS) is the most important risk factor for early-onset sepsis in newborns. We aimed to determine the rate of GBS colonisation in pregnant women evaluate the concordance between culture and a novel commercial polymerase chain reaction (PCR) test for screening. We also aimed to investigate the presence of the hypervirulent ST-17 clone and the potential risk factors that may affect colonisation.

A total of 365 rectovaginal samples from pregnant women ≥36 weeks were investigated. Lim Broth was used for culture. PCR was done by the Bio-Speedy GBS (Group B Streptococcus) qPCR kit. The presence of the hypervirulent ST-17 clone was evaluated by PCR. Potential risk factors were evaluated via a survey.

GBS was detected in 12.3 % (95 % CI: 9.3-16.1) of pregnant women by culture, in 15.3 % (95 % CI: 11.9-19.5) by direct qPCR and in 19.5 % (95 % CI: 15.6-23.9) by enrichment qPCR. Cohen's Kappa analysis revealed an 'almost perfect' level of agreement between culture and direct qPCR (κ = 0.85; 95 % CI: 0.74-0.97). Discordant results were observed in 13 cases (12 qPCR positive / culture negative, and one qPCR-negative / culture-positive). All isolates were susceptible to penicillin, while resistance to erythromycin and clindamycin were 37.8 % (95 % CI 25.1-52.4) and 33.3 % (95 % CI 21.4-47.9), respectively. ST-17 clone constituted 7 % (95 % CI:1.9-17.0) of the positive samples. GBS colonisation showed an association with sexual activity that approached the statistical significance threshold, and a significant association with education level.

Using a novel PCR test, almost perfect agreement was found between qPCR and culture, while the detection of colonisation was higher by qPCR. This study highlights the diagnostic contribution of molecular methods in GBS screening, even providing results after the onset of labor. The high prevalence of GBS, along with the circulation of hypervirulent clones underscores the critical importance of routine screening in pregnant women.