Phenotypic and Genotypic Characterization of Novel Polyvalent Bacteriophages With Potent In Vitro Activity Against an International Collection of Genetically Diverse Staphylococcus aureus

Abstract

Phage therapy recently passed a key milestone with success of the first regulated clinical trial using systemic administration. In this single-arm non-comparative safety study, phages were administered intravenously to patients with invasive Staphylococcus aureus infections with no adverse reactions reported. Here, we examined features of 78 lytic S. aureus phages, most of which were propagated using a S. carnosus host modified to be broadly susceptible to staphylococcal phage infection. Use of this host eliminates the threat of contamination with staphylococcal prophage — the main vector of S. aureus horizontal gene transfer. We determined the host range of these phages against an international collection of 185 S. aureus isolates with 56 different multilocus sequence types that included multiple representatives of all epidemic MRSA and MSSA clonal complexes. Forty of our 78 phages were able to infect > 90% of study isolates, 15 were able to infect > 95%, and two could infect all 184 clinical isolates, but not a phage-resistant mutant generated in a previous study. We selected the 10 phages with the widest host range for in vitro characterization by planktonic culture time-kill analysis against four isolates:- modified S. carnosus strain TM300H, methicillin-sensitive isolates D329 and 15981, and MRSA isolate 252. Six of these 10 phages were able to rapidly kill, reducing cell numbers of at least three isolates. The four best-performing phages, in this assay, were further shown to be highly effective in reducing 48 h biofilms on polystyrene formed by eight ST22 and eight ST36 MRSA isolates. Genomes of 22 of the widest host-range phages showed they belonged to the Twortvirinae subfamily of the order Caudovirales in three main groups corresponding to Silviavirus, and two distinct groups of Kayvirus. These genomes assembled as single-linear dsDNAs with an average length of 140 kb and a GC content of c. 30%. Phages that could infect > 96% of S. aureus isolates were found in all three groups, and these have great potential as therapeutic candidates if, in future studies, they can be formulated to maximize their efficacy and eliminate emergence of phage resistance by using appropriate combinations.

Isolation and in vitro characterization of novel S. epidermidis phages for therapeutic applications

“…To demonstrate the differences in efficacy depending on the characteristics of the strain, the phages COP-80A, COP-80B, and COP-110 were tested on the production host COB-Sec1 and biofilm proficient clinical isolate COB-SE3. They were significantly more effective against the production organism for all MOIs tested, but the time they inhibited the growth of COB-SE3 was still longer than 15 h, which is similar to previous observations ( Alves et al., 2014 ; Whittard et al., 2021 ). Since biofilm is critical for virulence of S. epidermidis , the effect on mature 24 h-old biofilm was examined using bright field microscopy.…”

Characterization of vB_Sau_S90, and vB_Sau_S165, a Broad Host Range Phages, and Multiple Phage Doses as a Potential Therapeutic Strategy to Eliminate Transient Phage Resistant Mutants in Staphylococcus Aureus

“…The experimental ndings by Whittard et al observed the appearance of Pacman-like colonies (described as half-lysis colony type in this study) during phage-bacterial interaction, and they also found that most of them were susceptible to phage although they remained resistant to phage in the liquid medium (Whittard et al 2021). A study by Głowacka-Rutkowska et al demonstrated the equilibration of phage bacteria in a mixture in which the authors outlined that phage carrier state cells and phage resistant coexist in a mixture, and the resistant phenotype can be reverted upon removing the phage by subculturing (Glowacka-Rutkowska et al 2018).…”

Staphylococcus aureus Isolated from the Oral Cavity: Phage Susceptibility in Relation to Antibiotic Resistance

“…They also participate in the transmission of pathogenicity islands and are the primary carrier of chromosomal and extrachromosomal genes during horizontal gene transfer (HGT) [ 31 ]. Phages can transfer genes of various staphylococcal virulence factors, including Panton–Valentine leucocidin, staphylokinase, enterotoxins, chemotaxis inhibitory proteins, and exfoliative toxins [ 32 , 33 ]. This may explain the association between the sensitivity of S. aureus to some phages and their pathogenicity.…”