GBS Mutations Identified: Explaining Post-Treatment Persistence and Infant Transmission

A new study by Michigan State University (MSU) researchers has identified mutations in Group B Streptococcus (GBS) strains, potentially explaining why some mothers continue to carry the bacteria after antibiotic treatment and can transmit it to infants.

Key Discoveries

These GBS strains, found in the birth canal, demonstrate an ability to survive and resist treatment due to these mutations. This resistance can lead to serious illnesses in newborns and infants.

This resistance can lead to serious illnesses in newborns and infants, including pneumonia, meningitis, and sepsis.

The research, published in mBio, marks the first identification of GBS strains as "mutators." These are bacteria characterized by significantly increased mutation rates, which result from defects in their DNA repair mechanisms.

This discovery represents an initial step toward understanding how GBS evades antibiotic treatment and aims to facilitate the identification of new drug targets to prevent or treat late-onset GBS infections in infants.

Understanding Group B Streptococcus

GBS is a common bacterium present in the microbiota of healthy individuals, typically residing in the gastrointestinal and genital tracts. Up to one-third of pregnant women may carry GBS in their birth canal, posing a risk of transmission to the baby during childbirth.

Since the 1990s, standard practice has involved screening pregnant women for GBS late in pregnancy and administering antibiotics during labor to reduce bacterial load at delivery.

This method, known as intrapartum antibiotic prophylaxis (IAP), has significantly reduced early-onset GBS infections (occurring within the first seven days of life) by over 80%.

The Unsolved Puzzle of Late-Onset Disease

Despite the success of IAP, the prevalence of late-onset GBS disease, which affects infants between one week and three months of age, has remained largely unchanged. The reasons for this consistent prevalence have been unclear.

To investigate this, researchers collected GBS samples from 212 pregnant women before treatment and again six weeks postpartum.

Despite receiving IAP, nearly 60% of the women re-tested positive for GBS at the postpartum screening.

Genomic comparisons of GBS strains from 34 women revealed high similarity between prenatal and postpartum samples. This finding suggests that antibiotics did not completely eradicate the bacteria.

The postpartum GBS strains did not show traditional antibiotic resistance genes; instead, they presented other mutations that may impact their survival, such as those related to cell division and adherence. Additionally, changes in biofilm production were noted in some postpartum strains.

Next Steps in Research

The research team has cataloged over 500 mutations. Future efforts will concentrate on determining how these mutations influence bacterial survival in laboratory and model systems, with the goal of developing new therapeutics or prevention strategies.