Final answer:
Cefoxitin is the correct antibiotic used as a surrogate marker for oxacillin resistance in Staphylococcus aureus, indicating susceptibility or resistance to methicillin and oxacillin.
Step-by-step explanation:
The correct option is c. Cefoxitin. Cefoxitin is a cephamycin antibiotic that serves as a surrogate marker for oxacillin resistance in tests for Methicillin-resistant Staphylococcus aureus (MRSA). This is because the presence of cefoxitin resistance often correlates with resistance to methicillin and, by extension, oxacillin. Hence, if a strain of S. aureus is found to be susceptible to cefoxitin, it is generally considered susceptible to oxacillin as well.