Acute osteomyelitis is most frequently caused by:

Acute osteomyelitis is usually a polymicrobial infection. Different types of organisms may be cultured from these lesions; the most common are Staphylococcus aureus and Staphylococcus albus, and various streptococci. Anaerobes such as Bacteroides, Porphyromonas or Prevotella species also predominate. Ref: Shafer's textbook of oral pathology 7th edition page 493