If only.
Not only can resistant S. aureus (MRSA) not be distinguished from susceptible (MSSA) strains under the microscope, they can’t even be distinguished from other, far less pathogenic species of Staphylococcus, such as S. epidermidis or S. hemolyticus.
S. epidermidis, a harmless skin commensal
S. aureus – sometimes a commensal, sometimes a deadly pathogen
Both would be reported by a clinical lab as “Gram-positive cocci in clusters”, leaving a physician to guess as to whether the patient has a potentially invasive infection requiring aggressive treatment, or just contamination with a usually harmless skin commensal.
Even in the restricted universe of the few dozen most common pathogens, there just aren’t that many traits discernible by microscopy (size, shape, clustering, differential staining) to reliably distinguish one species of pathogen from another. Distinguishing resistance traits within species is a problem that no one has solved.