Vertical transmission ofStreptococcus agalactiaecan cause neonatal infections. A culture test in the late stage of pregnancy is used to screen for the presence of maternalS. agalactiaefor intrapartum antibiotic prophylaxis. For the test, vaginal-rectal swab sampling is immediately followed by enrichment culture and bacterial identification. In some cases,Enterococcus faecaliscompetes with and overgrowthsS. agalactiaein the enrichment culture. Consequently, the identification test occasionally

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... elds false-negative results. Bacterial viruses, bacteriophages (phages), infect and kill specific host bacteria. In the current study, we explored the feasibility of using phages to minimize the undesirableE. faecalisoutgrowth and facilitateS. agalactiaedetection in an experimental setting. Phage mixture was prepared using three phages that specifically infectE. faecalis: phiEF24C, phiEF17H, and phiM1EF22. The mixture inhibited the growth of 86.7% (26/30) ofE. faecalisstrains tested in the enrichment broth. When single strains ofE. faecalisandS. agalactiaewere inoculated in the enrichment broth containing the phage mixture, bacterial growth was inhibited or facilitated, respectively. Further, several sets ofS. agalactiaeandE. faecalisstrains were co-cultured, and bacteria were detected on chromogenic agar after the enrichment culture.S. agalactiaewas dominant after plating a phage mixture-treated co-culture, while it was barely detected after plating the untreated co-culture. Considering these observations, the phage mixture can be employed in theS. agalactiaeculture test to increase test accuracy.