Evaluation and Characterization of Lytic Phages and their Recombinant Endolysins for Control of Staphylococcus aureus aiming to mitigate bovine mastitis

Abstract

As a natural alternative to conventional antimicrobials, bacteriophages are emerging as highly effective biocontrol agents against Staphylococcus aureus and other pathogenic bacteria. Due to the wide diversity of S. aureus types and the emergence of antibiotic-resistant strains, the search for highly lytic and prevalent bacteriophages against S. aureus is justified. In this study, we sought to characterized the lytic Phage 2 and Phage 4 biologically and morphologically and their recombinant endolysins EndF2 and EndF4. Transmission electron microscopy analysis revealed that these phages exhibited a structure with a polyhedral head and non-contractile tail, typical characteristics of the Siphoviridae family. Host spectrum identification showed that Phage 2 lysed 62.2% (N=90) of S. aureus strains and Phage 4 lysed 51.1% (N=90). In vitro tests with extracorporeal cow teats indicated that Phage 2 reduced the S. aureus load by up to 78.7%. Furthermore, recombinant endolysins EndF2 and EndF4 have catalytic and recognition/binding domains in their structures related to lytic activity, and both endolysins do not present critical aspects of allergenicity. Furthermore, EndF2 lysed 71.4% (N=42) and EndF4 lysed 76.2% (N=42) of the S. aureus strains tested. These findings indicate that Phages 2 and 4 and their recombinant endolysins EndF2 and EndF4 could potentially be used as tools for the prevention and control of S. aureus, suggesting they are potentially valuable biocontrol agents to mitigate the spread of S. aureus in the dairy industries and production chain.