Isolation and characterization of novel Staphylococcus aureus bacteriophage Hesat from dairy origin.

A novel temperate phage, named Hesat, was isolated by the incubation of a dairy strain of Staphylococcus aureus belonging to spa-type t127 with either bovine or ovine milk. Hesat represents a new species of temperate phage within the Phietavirus genus of the Azeredovirinae subfamily. Its genome has a length of 43,129 bp and a GC content of 35.11% and contains 75 predicted ORFs, some of which linked to virulence. This includes (i) a pathogenicity island (SaPln2), homologous to the type II toxin-antitoxin system PemK/MazF family toxin; (ii) a DUF3113 protein (gp30) that is putatively involved in the derepression of the global repressor Stl; and (iii) a cluster coding for a PVL. Genomic analysis of the host strain indicates Hesat is a resident prophage. Interestingly, its induction was obtained by exposing the bacterium to milk, while the conventional mitomycin C-based approach failed. The host range of phage Hesat appears to be broad, as it was able to lyse 24 out of 30 tested S. aureus isolates. Furthermore, when tested at high titer (108 PFU/ml), Hesat phage was also able to lyse a Staphylococcus muscae isolate, a coagulase-negative staphylococcal strain. KEY POINTS: • A new phage species was isolated from a Staphylococcus aureus bovine strain. • Pathogenicity island and PVL genes are encoded within phage genome. • The phage is active against most of S. aureus strains from both animal and human origins.

Anti-Staphylococcal Activity of the Auranofin Analogue Bearing Acetylcysteine in Place of the Thiosugar: An Experimental and Theoretical Investigation.

Auranofin (AF, hereafter) is an orally administered chrysotherapeutic agent approved for the treatment of rheumatoid arthritis that is being repurposed for various indications including bacterial infections. Its likely mode of action involves the impairment of the TrxR system through the binding of the pharmacophoric cation [AuPEt3]+. Accordingly, a reliable strategy to expand the medicinal profile of AF is the replacement of the thiosugar moiety with different ligands. Herein, we aimed to prepare the AF analogue bearing the acetylcysteine ligand (AF-AcCys, hereafter) and characterize its anti-staphylococcal activity. Biological studies revealed that AF-AcCys retains an antibacterial effect superimposable with that of AF against Staphylococcus aureus, whereas it is about 20 times less effective against Staphylococcus epidermidis. Bioinorganic studies confirmed that upon incubation with human serum albumin, AF-AcCys, similarly to AF, induced protein metalation through the [AuPEt3]+ fragment. Additionally, AF-AcCys appeared capable of binding the dodecapeptide Ac-SGGDILQSGCUG-NH2, corresponding to the tryptic C-terminal fragment (488-499) of hTrxR. To shed light on the pharmacological differences between AF and AF-AcCys, we carried out a comparative experimental stability study and a theoretical estimation of bond dissociation energies, unveiling the higher strength of the Au-S bond in AF-AcCys. From the results, it emerged that the lower lipophilicity of AF-AcCys with respect to AF could be a key feature for its different antibacterial activity. The differences and similarities between AF and AF-AcCys are discussed, alongside the opportunities and consequences that chemical structure modifications imply.