A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102degF. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?

Staphylococcus aureus is a well-known pathogen that is very opportunistic and commonly causes abscess lesions. It routinely may resist phagocytosis by WBCs due to protein A. Osteomyelitis and arthritis, either hematogenous or traumatic, are commonly caused by S. aureus, especially in children. Salmonella are gram-negative. Staphylococcus saprophyticus is a common skin flora and is usually not pathogenic. Streptococcus pneumoniae is seldom or never involved in osteomyelitis infections, as is true for L. monocytogenes.