Potential Application of Bacteriophages in Enrichment Culture for Improved PrenatalStreptococcus agalactiaeScreening

Abstract

18Vertical transmission of Streptococcus agalactiae can cause neonatal infections. A culture 19 test in the late stage of pregnancy is used to screen for the presence of maternal S. 20 agalactiae for intrapartum antibiotic prophylaxis. For the test, vaginal-rectal swab sampling 21 is immediately followed by enrichment culture and bacterial identification. In some cases, 22Enterococcus faecalis competes with and overgrowths S. agalactiae in the enrichment 23 culture. Consequently, the identification test occasionally yields false-negative results. 24Bacterial viruses, bacteriophages (phages), infect and kill specific host bacteria. In the 25 current study, we explored the feasibility of using phages to minimize the undesirable E. 26 faecalis outgrowth and facilitate S. agalactiae detection in an experimental setting. Phage 27 mixture was prepared using three phages that specifically infect E. faecalis: phiEF24C, 28 phiEF17H, and phiM1EF22. The mixture inhibited the growth of 86.7% (26/30) of E. 29 faecalis strains tested in the enrichment broth. When single strains of E. faecalis and S. 30 agalactiae were inoculated in the enrichment broth containing the phage mixture, bacterial 31 growth was inhibited or facilitated, respectively. Further, several sets of S. agalactiae and E. 32 faecalis strains were co-cultured, and bacteria were detected on chromogenic agar after the 33 enrichment culture. S. agalactiae was dominant after plating a phage mixture-treated 34 . CC-BY-NC-ND 4.0 International license It is made available under a was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint (which . http://dx.doi.org/10.1101/384222 doi: bioRxiv preprint first posted online Aug. 3, 2018; 3 co-culture, while it was barely detected after plating the untreated co-culture. Considering 35 these observations, the phage mixture can be employed in the S. agalactiae culture test to 36 increase test accuracy. 37 38