S. aureus is indeed gram-positive but within the bacteria classed as gram-positive, there are differences that might predispose them to infection by phages.
S. aureus as an organism usually adapts to their environment through mutations on their membranes which can be proteins e.g. surface proteins, or receptor molecules e.g. sugar receptors.
In preventing invasion by phages, mutations are gained that prevents attachment to the bacteria cell surface. This effectively prevents the binding of the phage to the bacteria thus preventing infection.
It is also worthy to note that the differences in bacteria strain could range from a few nucleotides to large variations in chromosomes and thus can aid in identifying specific strains that might have beneficial factors in the context of disease prevention.
To learn more about gram-positive bacteria see: https://brainly.com/question/9640110?referrer=searchResults
