Genomic Analysis of the Type VII Secretion System (T7SSb) Proteins in Staphylococcus aureus Isolates from Raw Meat, Processed Meat Products and Veterinary Samples of Food-Producing Animals

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Abstract
Staphylococcus aureus (S. aureus) produces an array of virulence factors (VFs), which contribute to its pathogenicity. One of the VFs is the type VII secretion system (T7SS), a protein secretion apparatus present in many Gram-positive bacteria, which plays a major role during the onset of infection. This study aimed to investigate the presence of secreted effector proteins and core structural proteins of the T7SS of S. aureus isolated from raw meat, processed meat products, and veterinary samples of food-producing animals. Whole-genome sequencing (WGS) and bioinformatics tools were employed to analyze S. aureus (n = 27) isolates. The results revealed that all 27 isolates investigated harboured various genes encoded by the T7SSb: secreted effector proteins (EsxA and EsxB) and core structural proteins (EssA, EssB, EssC, EsaA, and EsaB). The presence and absence of certain genes were observed, but overall, all these isolates harboured the major protein EssC. The EssC C-terminal found in these isolates was found to be conserved, and they clustered between the EssC1 and EssC3 variants. Ramachandran plot validations and predictions indicated the stability and likely operating conservation of T7SSb proteins. An analysis of protein–protein interactions, transmembrane domains, and secondary structures offered a thorough understanding of T7SSb assembly and how various proteins interact with each other. The results revealed that the isolates contained an array of T7SSb proteins, indicating the presence of proteins associated with various human infections, which highlights the practical application of a continuous surveillance monitoring programme and investigation of S. aureus strains.

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