Mutant Strep Strains Linked to Newborn Infections

Got story updates? Submit your updates here. ›

A new study from Michigan State University has found that certain mutant strains of Group B Streptococcus (GBS) bacteria can survive antibiotic treatment and still infect newborns, leading to serious illnesses like pneumonia, meningitis, and sepsis. The researchers discovered that these "mutator" strains have defects in their DNA repair machinery, allowing them to rapidly evolve and evade treatment, even after the mother receives antibiotics during labor.

Why it matters

GBS is a leading cause of illness and death in newborns, but the introduction of intrapartum antibiotic prophylaxis (IAP) in the 1990s has reduced early-onset GBS infections by over 80%. However, late-onset GBS disease in infants between 1 week and 3 months old has remained a persistent problem, and this new research provides insights into how the bacteria are adapting to avoid being eliminated by antibiotics.

The details

The researchers collected GBS samples from 212 pregnant women before and after childbirth, and found that nearly 60% of the women still tested positive for GBS 6 weeks after giving birth, even though they had received IAP. By comparing the genomes of the pre- and post-partum GBS strains, the team identified over 500 mutations that may be helping the bacteria survive antibiotic treatment and continue to infect newborns.

• The study was published in March 2026 in the journal mBio.
• The researchers collected GBS samples from pregnant women in their late-stage pregnancy and again 6 weeks after childbirth.

What they’re saying

What’s next

Future work will focus on determining how the identified mutations affect the bacteria's survival and ability to evade antibiotics, with the goal of finding new drug targets to prevent or treat late-onset GBS infections in babies.