As a leading cause of sepsis in the neonatal population, Streptococcus agalactiae or Group B Streptococcus (GBS) is a significant obstetric pathogen. As a result, numerous screening strategies have been implemented across the globe to identify mothers at risk of transmitting the organism to their newborn. Detection of GBS by culture screening and risk-based strategies all result in antibiotic administration. Although penicillin remains effective, resistance is inevitable and the impact of antibiotic administration on the maternal and neonatal microbiome during pregnancy is not well-understood. An ideal treatment option would be one in which GBS are targeted in colonized women, removing only GBS and having no effect on commensal organisms within the body. Use of bacterial viruses, known as bacteriophage (phage) therapy, is one such option and was used successfully for treating bacterial disease on numerous occasions in the pre-antibiotic era.
Vaginal and rectal swabs collected from 302 pregnant West Australian women were screened for GBS, resulting in 136 isolates purified from 78 participants. Filtered enriched supernatant from human wastewater was spot tested on these 136 antenatal strains and 10 additional neonatal GBS isolates to test for lytic activity. These processes resulted in the isolation of four bacteriophages.
One isolated bacteriophage displayed lytic activity against 117 antenatal GBS strains (86%), observed as clearing of the bacterial lawn. A total of 63 of the 78 study participants (81%) carried phage-sensitive GBS at both sites, or at either vaginal or rectal sites (9% of study participants). Two of the remaining three phages showed activity against all neonatal disease-causing strains (n=10) with the previously described phage also active against 90% of these strains (9/10). Transmission electron microscopy confirmed all phages as members of the Siphoviridae family.
The in vitro activity of these bacteriophages against a broad range of clinical strains is extremely promising for their future application as therapeutic agents and sequencing is currently underway to confirm the lytic nature of these viruses.