Potential Application of Bacteriophages in Enrichment Culture for Improved Prenatal Streptococcus agalactiae Screening

Abstract

Vertical transmission of Streptococcus agalactiae can cause neonatal infections. A culture test in the late stage of pregnancy is used to screen for the presence of maternal S. agalactiae for intrapartum antibiotic prophylaxis. For the test, a vaginal–rectal sample is recommended to be enriched, followed by bacterial identification. In some cases, Enterococcus faecalis overgrows in the enrichment culture. Consequently, the identification test yields false-negative results. Bacteriophages (phages) can be used as antimicrobial materials. Here, we explored the feasibility of using phages to minimize false-negative results in an experimental setting. Phage mixture was prepared using three phages that specifically infect E. faecalis: phiEF24C, phiEF17H, and phiM1EF22. The mixture inhibited the growth of 86.7% (26/30) of vaginal E. faecalis strains. The simple coculture of E. faecalis and S. agalactiae was used as an experimental enrichment model. Phage mixture treatment led to suppression of E. faecalis growth and facilitation of S. agalactiae growth. In addition, testing several sets of S. agalactiae and E. faecalis strains, the treatment with phage mixture in the enrichment improved S. agalactiae detection on chromogenic agar. Our results suggest that the phage mixture can be usefully employed in the S. agalactiae culture test to increase test accuracy.

Evaluation of Phage Therapy in the Context of Enterococcus faecalis and Its Associated Diseases

“…Meanwhile, some studies have shown the efficacy of phages, in vivo, against E. faecalis , using mouse models (Table 1). An intraperitoneal application of phages, significantly rescued mice, when deliberately challenged with the E. faecalis EF14 and E. faecalis VRE2 strains [95]. Similarly, another study has showed that mice treated with different phage doses were protected from the VREF systemic infection, and alleviated the gut microbial imbalance that occurred as a result of infection [91].…”

Use of Recombinant Endolysin to Improve Accuracy of Group B Streptococcus Tests

“…EG-LYS activity was examined using E. faecalis , Enterococcus faecium , Enterococcus avium , and GBS strains isolated from the vaginal swabs in the prenatal GBS screening test ( 17 ). First, EG-LYS activity on peptidoglycan and whole bacterial cells in PBS was analyzed.…”

“…We used 5, 30, 5, and 7 strains of E. avium , E. faecalis , E. faecium , and GBS, respectively, which were all isolated from clinical vaginal swabs and identified using mass spectrometry ( 17 ). In the case of GBS strains, the Lancefield B antigens were also tested using a kit (Strept LA “SEIKEN”; Denka Company, Niigata, Japan).…”

“…We previously reported the use of an E. faecalis -specific phage cocktail as an E. faecalis selective growth inhibitor in the prenatal GBS screening test ( 17 ). However, the introduction of this phage cocktail for clinical use in prenatal GBS screening tests could be limited by the following factors: (i) phages in the mixture must be monitored consistently because phage-insensitive or -resistant bacteria could emerge ( 18 ); (ii) the phage cocktail needs to be optimized, as the phages in the cocktail may interfere with each other ( 19 ); (iii) it may take longer than expected to prepare the phage cocktail, because the process for manufacturing each phage requires optimization ( 20 ); and (iv) the use of phages in clinical laboratories may cause phage contamination in clinical specimens ( 17 ).…”

Bacteriophage-Based Biotechnological Applications

“…Another interesting area of research is the application of phages in diagnosis, not to target the bacteria but instead to eliminate common sample contaminations, thus improving the target bacteria recovery and consequently improving detection. Jumpei Uchiyama and colleagues [13] used this approach to remove Enterococcus faecalis from vaginal samples, avoiding the overgrowth of these bacteria during the enrichment phase, allowing for the detection of Streptococcus agalactiae and decreasing the common high number of false negatives observed with vaginal S. agalactiae diagnosis.…”