Which organism is among the most common causes of vertebral osteomyelitis?

• A. Escherichia coli
• B. Pseudomonas aeruginosa
• C. Staphylococcus aureus
• D. Streptococcus pneumoniae

Answer: (C)

Staphylococcus aureus is the most common cause of vertebral osteomyelitis because bacteremia frequently seeds the spine, and S. aureus is the leading pathogen in hematogenous osteomyelitis in adults. Its ability to invade bone and vertebral endplates makes it the typical culprit when the infection reaches the spine, especially in patients with skin infections, IV drug use, or other bacteremic sources. Other organisms like Pseudomonas are more tied to IV drug use or healthcare exposure, E. coli to urinary or GI sources in older adults, and Streptococcus pneumoniae is a less common cause of spine infection.