Host range, morphological and genomic characterisation of bacteriophages with activity against clinical Streptococcus agalactiae isolates

Abstract

Streptococcus agalactiae or Group B Streptococcus (GBS) is a leading cause of sepsis in neonates. As a preventative measure prophylactic antibiotic administration is common in pregnant women colonised with GBS, but antibiotic-resistance and adverse effects on neonatal microbiomes may result. Use of bacteriophages (phages) is one option for targeted therapy. To this end, four phages (LF1-LF4) were isolated from wastewater. They displayed lytic activity in vitro against S. agalactiae isolates collected from pregnant women and neonates, with 190/246 isolates (77.2%) and 10/10 (100%) isolates susceptible to at least one phage, respectively. Phage genomes ranged from 32,205-44,768 bp and all phages were members of the Siphoviridae family. High nucleotide identity (99.9%) was observed between LF1 and LF4, which were closely related to a putative prophage of S. agalactiae. The genome organisation of LF2 differed, and it showed similarity to a different S. agalactiae prophage, while LF3 was more closely related to a Streptococcus pyogenes phage. Lysogenic gene presence (integrase, repressor and regulatory modules), was suggestive of temperate phages. In a therapeutic context, temperate phages are not ideal candidates, however, the broad host range activity of these phages observed on clinical isolates in vitro is promising for future therapeutic approaches including bioengineered phage or lysin applications.

Characterization of Clinical and Carrier Streptococcus agalactiae and Prophage Contribution to the Strain Variability

“…Low-level of similarity was detected for C and H prophages with S. suis phiNJ2 and prophage F with S. equi P9 phage [ 40 , 42 ]. Bacteriophages from groups D and G were relative to S. agalactiae phages LF2 and LF4 [ 20 ]. Group E bacteriophages were similar to S. agalactiae phage LF3 [ 20 ] and S. pyogenes phage Str03 [ 43 ] ( Figure 2 A; Table S4 ).…”

“…Bacteriophages from groups D and G were relative to S. agalactiae phages LF2 and LF4 [ 20 ]. Group E bacteriophages were similar to S. agalactiae phage LF3 [ 20 ] and S. pyogenes phage Str03 [ 43 ] ( Figure 2 A; Table S4 ).…”

“…Temperate bacteriophages of several pathogenic organisms affect virulence since they carry genes encoding toxins [ 8 ]. No such genes have been identified in S. agalactiae prophages [ 17 , 18 , 20 ]. However, some of the analyzed prophages contained genes that likely contribute to virulence and bacterial fitness ( Table S4 ).…”

“…Using the PCR approach, we further determined the content of prophages in a set of the 123 GBS isolates and observed correlation between sequence type and the presence of prophages. Studies on the temperate phages are important not only for determination of their virulence impact, but also as the source of phages as potential antimicrobial agents for management of GBS vaginal infections, since no lytic phage infecting GBS has been isolated to date [ 18 , 19 , 20 ].…”

Potential for Phages in the Treatment of Bacterial Sexually Transmitted Infections

“…Considered a concerning threat by CDC, clindamycin resistance prevalent, some erythromycin, azithromycin and vancomycin resistance reported [5] Considered a part of normal flora for 10-30% of women [55], the CDC estimates 27,000 severe cases of GBS infections in the US, with 49% (~13,230) being erythromycin-resistant and with 28% (~7560) being clindamycin-resistant [5]; a majority of infants colonized with GBS do not develop a GBS infection; about 60% of cases of early-onset GBS infection occur in neonates born to patients with negative GBS culture at 35-37 weeks [56] Leading cause of neonatal sepsis and meningitis [55]; asymptomatic in colonized women [57] Intravenous penicillin G (during labor); ampicillin or vancomycin may be substituted [56] Gram-positive, with ten different capsular types (Ia, Ib, II-XI) [58] Growth observed with normal laboratory conditions (37 • C and enriched media) [59,60] Temperate phages have been isolated and characterized for S. agalactiae [59,61,62]; phage lysins have successfully shown activity in vitro (lysins from S. agalactiae phages B30 [63,64], λSA2 [65] and λSA1 [66], as well as CHAP k lysin derived from S. aureus [67]) and in vivo (PlyGBS from phage NCTC11261 [68] and chimeric ClyV [69]). There can be a wide host range with streptococcal phages and phage enzymes [70,71]…”